Highway-I Lecture Slide

Highway Engineering-I

Chapter One:

INTODUCTION TO TRANSPORT SYSTEM AND PLANNING

ASTU/Civil Engineering Dept.

Instructor: Fasika Mekonnen

[email protected]

1

1. INTRODUCTION

2

Transportation is simply a movement of person, goods or information from place to place by different means like vehicles, airplane etc. for some particular purposes.

Transportation is a service created to serve society by linking locations where activity takes place such as markets, industries and factories, offices, schools and etc.

It penetrates into all phases of production and distribution of goods.

Transportation improvements: increase personal mobility, reduces travel time.

Permit greater freedom to people to choose, where to live or work and in the case of goods they lower the cost of production and distribution tending to national economic growth.


2. TRANSPORT SYSTEM

3

A system: a group or assemblage of parts or elements used for a common purpose so interrelated that a change in one component has an effect.

A transport system: as consisting of the fixed facilities, the flow entities, and the control system that permits people and goods to overcome friction of geographical space efficiently in order to participate in a timely manner in some desired activity.

Fixed facilities: are the physical components of the system that are fixed in space (e.g. Roadway segments, tracks, pipes, cableways, intersections/interchanges, transit terminals, harbors and ports etc.)

Flow entities: are the units that traverse the fixed facilities.

(e.g. vehicles, container units, railroads car, airplanes etc.)

Control system: consists of vehicular control. (e.g. Traffic sign & Signals)

Demand/Desired Activity: to serve people in undertaking their economic, social and cultural activities


Objective of Transportation system

4

helps in the movement of passengers and freight from one location to another.

relates the population to the land use.

acts as an integrating and coordinating factor in the highly complex and industrialized society.

provides the place utility and time utility to product.


Merits/Advantages of Transportation System

5

Economic Front: It relates population to land use by moving them from one place to

another. It increases the production by creating demand, easily availability

and reducing prices. It has vast potential of generating employment. New markets get developed near production centers.

Political Front: Different regions of the country are made interdependent. Transportation has developed a sense of national unity. Fulfills the defense and strategic needs of a country.

Social Front: Life becomes more enjoyable and comfortable. It provides emergency services available at your door. It has helped in raising the standards of living of people. The settlement pattern in the country is controlled by it.


Demerits/Disadvantages of Transportation System:

6

With the development of large scale industries the cottage industries have been eliminated.

The area loses its distinguishing characteristics.

The environmentalist pollutions related to air, water, noise, aesthetics, vibrations get increased and create health problems.

The expansion of transportation system sometimes affects the recreational activities provided in the area.

It has changed the traditions and customs of families along with modes of living.


Classification of Transportation System:

7

On the basis of ownership: i) Private

ii) Public

On the basis of type of load: i) Passenger

ii) Freight

On the basis of supporting systems: Road Transport: used automobiles, trucks, buses, tractor-

trailers, bicycles

Rail Transport: used trains , railway wagon etc.

Air Transport: used airplanes, helicopters, space crafts etc.

Water transport: used ship, submarines, boat etc.

Pipe Lines: used sewage, petroleum etc.

Cable ways: ….

Conveyors: ….


ASTU/Civil Engineering Dept. 8


http://en.wikipedia.org/wiki/File:ICE1_Schellenberg.jpg



http://en.wikipedia.org/wiki/File:Scandinavian_Airlines_Kiruna.jpg



Table 1: Relative Merits and Demerits

11

Factor Road Rail Air Water

Cost:

Vehicle

Terminal

Way Links

Maintenance

Low

Moderate

,,

,,

Moderate

,,

,,

,,

Moderate

,,

,,

,,

High

,,

Nil

High

Traffic type Fright & passenger Fright & passenger Fright & passenger Fright & passenger

Distance covered Small Moderate to Long Moderate to Long Moderate to Long

Speeds Low Medium V. High Low

Tonnage Low High Medium High

Fuel consumption (w.r.t. rail) 4.0 1.0 25.0 5.2

Flexibility Good Good Poor Fair

Employment potential High Low Low Low

Unit of Transport Single Assemblage Single Single

Personalized travel Possible Not Possible Possible Possible

Stationing problem Exist Not exist Not exist Not exist


Suitability of Transportation Systems

12

The systems and modes of transport are generally evaluated in terms of the basic attributes:

Accessibility and utility: distance and flexibility.

Mobility: handling capacity and speed.

Efficiency: direct and indirect cost of transportation.


Specialties in Transportation Engineering

13

Planning

deals with selection of projects, defining the problem, gathering and analyzing data, and evaluating various alternative solutions.

forecast of future traffic; estimate of impact of the facility on land use, the environment, the community; and determination of the benefits and cost that will result if the project is built.

Design

involves the specification of all features of the transportation system so that will function smoothly, efficiently, and in accord with physical laws.

used for estimating the facility costs and for carrying out its construction.


Specialties in Transportation Engineering


Construction

Generally the construction activities include any construction work of the project that has been defined during the design stage.

Traffic Operation

the elements of the concern are traffic accident analysis, parking, loading, design of terminals facilities, traffic signs, marking, signals, speed regulation and highway lighting.

Maintenance

involves all work necessary to ensure that the highway system is kept in proper working order

3. TRANSPORT PLANNING

15

Transportation Planning:

determination of future goals that is expected from the transportation system that is expected to be built.

Objectives: to build or improve various parts of transportation system

includes studies, planning and realization of strategies to supply the requirement of transport services to meet transport demand.

Transport projects are normally justified for improvement of traffic flow and safety, saving the travel time and energy consumption, economic growth and increased accessibility.


Basic Elements of Transportation Planning

16

The transportation planning comprises seven basic elements, which are interrelated and are not carried out necessarily sequentially.

Facility inventory

Socio-economic and Land-use

Goals and objectives

Identify system deficiencies and opportunities

Developing and analyze alternatives

Evaluate alternatives

Action plan and implementation

Monitor System Performance




Basic Elements of Transportation Planning 1. Facility inventory

18

inventory of the existing transport facilities, their condition and performance.

The most common transport system inventory involves: Travel time and delay studies

Traffic flow surveys

Maintenance and operation costs

Describe of the existing transport services

The available facility and their condition

Example-For a highway planning the inventory may involve

Function classification: Major/Minor arterial, Local or Collector road.

Physical features of the road: No. of lane, Traffic control devices/signals , pavement width.

Traffic volume delay

Travel time along the route


19

involves all the activities required to understand the situation that give rise to the perceived need for a transportation improvement.

considered which relates trip making to the type of activities that occur in a region and also to the characteristics of the trip maker that will influence the way this trips are made.

The type of data on trip maker characteristics include: Level of income Number of members in house hold Number of vehicles in house hold Age composition of house hold Education level Employment etc.

Examples of land use: shopping center, industrial areas, residential areas, Offices etc…


2. Socio-economic and Land-use


20

Goals are generalized statements that indicate the desired achievement of transportation plan.

Objectives are more specific statements that indicate the means by which these goals will be achieved.

Examples: Goals: “The transportation system should meet the mobility needs

of the population” Objectives: “Provide transit service to major markets in the

region.” To identify objectives and related problems there are two types of

approaches The problem oriented approach: starts with defining problem The objective-led approach: starts with defining objectives and indicators

Some of the possible set of objectives: Safety Accessibility: ease of reaching: Sustainability Environmental protection Economic efficiency Economic regeneration

Basic Elements of Transportation Planning 3. Goals and objectives


21

Transport planning identifies and prioritizes those elements of transport systems where problems exist today or where problems exist in further given growth in travel.

Also transport planning can also identify areas where significant problem do not exist this time, but system can provide opportunities for enhanced efficiency of operation.

Basic Elements of Transportation Planning 4. Identify system deficiencies and opportunities


22

Consideration is given to a variety of ideas, designs, locations, and system configurations that might provide solutions to the problems.

include preliminary feasibility studies, data gathering field testing and cost estimating may be necessary at this stage to determine the practicability and financial feasibility of the alternative being proposed.

Example- Improvement of highways

New construction

Adding new lanes

Improving traffic controls through signals, signs etc.

Improving traffic flow through canalization.

Basic Elements of Transportation Planning 5. Developing and analyze alternatives


23

Determine how well each alternative achieve the objectives of the project as defined by the criteria.

Evaluation involves methods for comparing in an analytic way relative value of the alternatives.

Mostly used approaches is the benefit/cost ratio.

The benefit cost ratio is the means of identifying the most economical efficient alternative by defining benefits and costs.

Basic Elements of Transportation Planning 6. Evaluate alternatives


24

Once the transport project has been selected, a detail design phase begins, in which each of the components of the facility is specified.

this involves physical location, geometric dimension, and structural configuration.

Design plans are produced that can be used to estimate the cost of building the project.

Monitor System Performance Continually examines the performance and condition of the

transportation system to identify where improvements can be made.

necessary to systematically identify areas where improvements might occur.

Basic Elements of Transportation Planning 7. Action plan and implementation


Thank You!


QUESTIONS?

25


Chapter Two:

HIGHWAY ROUTE SURVEYS AND LOCATION



[email protected]

1

1. HIGHWAY ALIGNMENT


Objective: establishment of the new highway’s centerline

and cross-sections in relation to the terminal points and to

the topography through which the highway will pass.

Centerline determines the amount of cut and fill, cross-

section details, drainage design, construction costs and

environmental impacts.

Improper alignment would increase;

Construction cost

Land acquisition cost

Maintenance cost

Vehicle operation cost

Accident rate

2

HIGHWAY ALIGNMENT…(Cond..)


Different types of highway have different needs.

Requirements of ideal alignment:

Short

Easy

Construction, maintenance, vehicle operation

Safe

low accident, stable foundation)

Economical

Initial cost, maintenance cost, operation cost

3


Factors controlling alignment

Obligatory points

Traffic

Geometric design

Economics

Other considerations

2. FACTORS CONTROLLING ALIGNMENT

4

FACTORS CONTROLLING ALIGNMENT..(Cond..)


Obligatory points

Points through which the alignment is to pass

Bridges sites

Intermediate town b/n terminals

Mountainous pass

Points through which the alignment should not pass

Very costly structures

Highly developed expensive land areas

Cultural or religious places

Hospitals, schools etc

5



Traffic

The alignment should suit traffic demand

The alignment should kept in view of the desire lines, flow patterns and future trend

Geometric design:

Grades, radius of curves, sight distance etc

First determine standard of the road and then

Fix the geometric standards

Economy:

Includes the initial cost, maintenance cost and operation cost

If high embankment and deep cuts are avoided there would be a decrease in initial cost

In minor roads: Grades-steep, Curves-sharp

6



Other considerations:

Drainage consideration

Guide the vertical alignment

Hydrological factors

Subsurface water level, seepage flow, high flood level

Political considerations

7

3. ROUTE SURVEY


The purpose of the route survey is to fix the road

alignment i.e. to position the central line of the road

on the ground.

The work of the highway location survey may include

Desk study

Reconnaissance surveys

Preliminary surveys

Final location & detailed surveys

8

ROUTE SURVEY 1. Desk study


ROUTE SURVEY 1. Desk study


If the topographic map of the area is available it is

possible to suggest the likely routes of the road

The following details help to locate the routes:

Alignment avoiding valleys, ponds or lakes

Possibility of crossing through mountain pass

Approximate location of bridges sites for crossing

river

Consider alternate routes by keeping the

permissible gradient

10

ROUTE SURVEY 2. Reconnaissance surveys


To examine the general character of the area

Helps to decide the most feasible routes for detailed

studies

A field survey party may inspect a fairly broad stretch

of land along the proposed alternatives routes of the

map in the field

All relevant details not available in the map are

collected & noted down

11

ROUTE SURVEY 2. Reconnaissance surveys (Cont..)


The following are some of the details to be collected:

Valleys, ponds, lakes, marshy land

Approximate values of gradient, length of gradients

Number & type of cross-drainage structures, max.

flood level

Soil survey

Sources of construction materials, water & location

of stones

12

ROUTE SURVEY 2. Reconnaissance surveys (Cont..)


Useful checklists:

Design standards

Grading & earthwork

Foundation condition

Geological conditions

Drainage

Right of way

Effect on community

Traffic characteristics & maintenance cost

13

ROUTE SURVEY 3. Preliminary survey


Objective:

To survey the various alignments proposed & collect all

necessary details of topographic drainage & soil

To compare the different proposals in view of the

requirements of a good alignment

To estimate the quantity of earthwork, material and to

workout the cost of alternative proposals.

To finalize the best alignment from all consideration

Methods:

Conventional method

Aerial photographic method

14

ROUTE SURVEY 3. Preliminary survey(cont..)


1. Conventional method

Ground survey is carried out

Collect topographical data

Carries out soil survey

Procedures for conventional method:

Primary traverse

Topographic features

Leveling work- CL profiles & X-sections

Drainage- type, number & size of Drainage structures

Soil survey- slope, pavement type & thickness

15

ROUTE SURVEY 3. Preliminary survey(cont..)


2. Aerial photography method

It is a modern approach by taking aerial

photographs (proposed corridor) & using photo

interpretation technique to obtain the necessary

topographic, soil and geological data.

Then PS of various alternate alignments, a

comparative is made.

Finally the most suitable alignment is selected.

16

ROUTE SURVEY 4. Final location survey


Purpose:

To fix the centerline of the selected alignment on the ground and

To collect additional data for the design and preparation of working drawings.

Features of the final location survey:

Pegging the center line

centerline leveling

X-section leveling

Intersecting road

The direction w.r.t the CL of all intersecting roads should be measured.

Profiles and x- section

Ditches and streams

Profile and X-section leveling helps for location and construction of culverts and bridges.

17

Example:

Alternative#1


Alternative #2


Alternative #3


Route Selection


Thank You!


QUESTIONS?

22


Chapter Three:

GEOMETRICAL DESIGN OF HIGHWAY



[email protected]

1. INTRODUCTION


Highway geometric design is the process whereby the layout of the road through the terrain is designed to meet the needs of the road users.

Geometric features are the road cross-section and horizontal and vertical alignment.

highway geometric elements:

Cross-section

Horizontal alignment

Vertical alignment

Sight distance

Vertical and lateral clearance

Intersections

2. DESIGN CONTROL AND CRITERIA


The choice of design controls and criteria is influenced by

the following factors:

the functional classification of the road;

the nature of the terrain;

the design vehicle;

the traffic volumes expected on the road;

the design speed;

the density and character of the adjoining land use;

economic and environmental considerations.

Functional Classification of Roads


The classification of highways into different operational systems, functional

classes, or geometric types is necessary for communication among

engineers, administrators, and the general public.

A complete functional design system provides a serious of distinct travel

movements. The six recognizable stages in most trips include :

•Main movement freeway uninterrupted high-speed flow

•Transition freeway ramps

•Distribution (arterials) moderate speed

•collection brings them nearer

to the vicinity of their destination

neighborhoods

•Access direct approach to individual residence s

•Termination

Functional Classification of Roads…(cond..)


Road class as per ERA Geometric Design Manual (2002)

The functional classification in Ethiopia includes five functional classes Trunk Roads (Class I): Centers of international importance and roads

terminating at international boundaries are linked with Addis Ababa by trunk roads. Trunk roads have a present AADT >=1000, although they can have volumes as low as 100 AADT

Link Roads (Class II):Centers of national or international importance, such as principal towns and urban centers, must be linked between each other by link roads. A typical link road has over 400 - 1000 first year AADT, although values can range between 50-10,000 AADT.

Main Access Roads (Class III):Centers of provincial importance must be linked between each other by main access roads. First year AADTs are between 30-1,000.

Collector Roads (Class IV):Roads linking locally important centers to each other, to a more important center, or to higher class roads must be linked by a collector road. First year AADTs are between 25-400.

Feeder Roads (Class V):Any road link to a minor center such as market & local locations is served by a feeder road. First year AADTs are b/n 0-100.





the highway network plays in providing:

access to property: direct access

to adjacent property

travel mobility: continuous travel



In this diagram, lines of travel desire are shown as straight lines connecting trip origins and destinations. Relative widths of lines indicate relative amounts of travel desire. Relative sizes of circles indicate relative trip generating or attracting power.

Note that the heavy travel movements are directly served or nearly so; and that the lesser ones are channeled into somewhat indirect paths.

The facilities shown in the diagram have been labeled local, collector and arterial; terms which are descriptive of their functional relationships. Note particularly that this hierarchy of functional types relates directly to the hierarchy of travel distances which they serve.

Topography and Land Use


Topography, physical features and land use have a great effect on road locations and geometrics.

Design elements affected are:

Grades affected by hills,

Sight distance valleys, rivers

Cross-sections steep slopes

Speeds etc.

Ethiopian Road Authority classifies terrain as:

flat,

rolling,

mountainous and

escarpment.

Topography and Land Use…(cont.)


1. Flat terrain: Flat or gently rolling country, which offers few obstacles to the

construction of a road, having continuously unrestricted horizontal and

vertical alignment (transverse terrain slope up to 5 percent).



2. Rolling terrain: Rolling, hilly or foothill country where the slopes generally rise

and fall moderately and where occasional steep slopes are encountered, resulting in some restrictions in alignment

transverse terrain slope from 5 percent to 25 percent



3. Mountainous terrain:

Rugged, hilly and mountainous country and river gorges. This class of terrain imposes definite restrictions on the standard of alignment obtainable and often involves long steep grades and limited sight distance.(transverse terrain slope from 25 to 50 %



4. Escarpment terrian:

Other terrains not classified under the above terrain types.

Transversal slope above 50%

Design Vehicle


Key controls in geometric highway design are the

physical characteristics and the proportions of vehicles of

various sizes using the highway and turning capabilities of

vehicles.

Controls in geometric design:

Max. gradient

Lane width

Horizontal curve Radius

Horizontal curve widening

Junction design

Design Vehicle ….(cont.)


According to AASHTO there are 4 classes

Passenger cars

Buses

Trucks

Recreational vehicles

ERA’s four design vehicles:

Utility vehicle DV1

Single unit truck DV2

Single unit bus DV3

Semi-trailer combination DV4

Design Vehicle ….(cont.)


Driver Characteristics


Geometric design of a highway should consider users,

especially drivers’ performance limits. There are limits to

a driver’s vision, perception, reaction, concentration,

comfort that could impact the highway safety and

operating efficiency.

Example:

the average brake-reaction time of a driver (including decision

time), is 2.5 sec which important in determining sight distance

in highway geometric design

Design Volume


Traffic volume is number of vehicles that pass a point along

a roadway during a specified time period.

directly affects features of design such as:

number of lanes, widths, alignments, and gradients.

Annual Average Daily Traffic (AADT): during a period of 24

consecutive hours averaged over a period of 365 days.

Average Daily Traffic (ADT): is the average of 24-hr counts

collected over a number of days greater than one but less

than a year.

one truck is often equivalent to several passenger cars.

Design Speed


determine the various geometric design features of the roadway.

Depends on:

Functional classification

Land use of adjacent area

Topography

Expected operating speed

Select as high a design speed as practical

directly related:

Curvature(radius), superelevation, and sight distance

Indirectly related:

widths of lanes and shoulders and clearances to walls and rails.

3. HIGHWAY CROSS-SECTION ELEMENTS


A cross-section will normally consist of the carriageway,

shoulders or curbs, drainage features, and earthwork

profiles

Carriageway- use by moving traffic: traffic lanes, auxiliary lanes,

climbing lanes, and passing lanes, and bus bays and lay-byes.

Roadway- consists of the carriageway and the shoulders,

parking lanes and viewing areas

Earthwork profiles- includes side slopes and back slopes

For urban cross-sections: facilities for pedestrians,

cyclists, or other specialist user groups

HIGHWAY CROSS-SECTION ELEMENTS…(cont.)


Highways are categorized into Divided highways

Undivided highways The distinction is based on the presence of median

The components of divided highways within the right of way are Highway Travel Lanes

Shoulders

Medians

Pavement Crowns

Curbs

Drainage Ditches

Sideslopes

Guardrails

I. Highway Travel Lanes


the portion of roadway provided for movement of vehicles

vary according to functional class of highway, design speed, traffic volume and level of development of the area.

Should accommodate the type & volume of traffic, assumed design speed

unequal-width lanes are used, locating the wider lane on the outside (right) provides more space for large vehicles that usually occupy that lane.

Example: Two-lane HW: 7.2m lane width

Table 2.1 of ERA manuals for all DS

II. Shoulders


Shoulders: attached with the travelled way for:

accommodation of stopped vehicles for emergency use

lateral support for the pavement structure.

recovery of errant vehicles

to increase sight distance on horizontal curves

to provide clearance for placement of road signs

provides additional space for bicycle use

They vary from no shoulder on minor rural roads where there is no surfacing, to a 1.5-3.0m or even greater sealed shoulder on major roads depending on the terrain and design classification.

II. Shoulders…(cont.)


Materials used to surface shoulders include:

gravel, shell, crushed rock, mineral or chemical additives, bituminous surface treatments

All shoulders should be sloped sufficiently to rapidly drain surface water

The slope of the shoulder should be greater than that of the pavement.

high type surfacing: slope from 2 to 4 percent.

Gravel :4 to 6 percent

grass shoulders : 6 to 8 percent slopes

the color and texture of shoulders be different from those of the traveled way

to clearly define the traveled way at all times

II. Shoulders…(cont.)


Shoulders widths as recommended by the ERA design Guide

Rural Terrain/Shoulder Width (m) Town Section Widths (m) Design Standard

Flat Rolling Mountainous Escarpment Shoulder Parking

Lane***

Foot

way

Median!

DS1 3.0 3.0 0.5 – 2.5 0.5 – 2.5 n/a 3.5 2.5

(min)

5.0 (min)

DS2 3.0 3.0 0.5 – 2.5 0.5 – 2.5 n/a 3.5 2.5 Barrier!

DS3 1.5 - 3.0++ 1.5 - 3.0++ 0.5 – 1.5 0.5 – 1.5 n/a 3.5 2.5 n/a

DS4 1.5 1.5 0.5 0.5 n/a 3.5 2.5 n/a

DS5* 0.0 0.0 0.0 0.0 n/a

3.5

+++ 2.5 n/a

DS6** 0.0 0.0 0.0 0.0 n/a 3.5+++

2.5 n/a

DS7 1.0 (earth) 1.0 (earth) 1.0 (earth) 1.0 (earth) n/a n/a + n/a + n/a

DS8** 0.0 0.0 0.0 0.0 n/a n/a + n/a + n/a

DS9** 0.0 0.0 0.0 0.0 n/a n/a + n/a + n/a

DS10** 0.0 0.0 0.0 0.0 n/a n/a + n/a + n/a

III. Medians


Median is the portion of a highway separating opposing directions of the traveled way.

The principal functions: to separate opposing traffic

provide a recovery area for out of- control vehicles,

provide a stopping area in case of emergencies,

allow space for speed changes and storage of left-turning and U-turning vehicles,

minimize headlight glare, and

provide width for future lanes.

Additional benefits: in an urban area are that it may offer an open green space,

may provide a refuge area for pedestrians crossing the street, and

may control the location of intersection traffic conflicts.

III. Medians…(cont.)


For maximum efficiency, a median should be highly visible both night and day and should contrast with the traveled

Median can be either raised, flush or depressed.

median widths is from 1.2 to 24 m or more

on freeways, a median barrier may be used

IV. Pavement Crowns


Pavement crown is the raising of the centerline of the

roadway above the elevation of the pavement edges but

not being so great as to make steering difficult.

to provide adequate surface drainage

normal crossfall should be 2.5% on paved roads and 4 5%

on unpaved roads

Unpaved shoulders on a paved road should be 1.5 %

steeper

When four or more traffic lanes are used, it is advisable

to provide a higher rate of crown on the outer lanes

IV. Pavement Crowns….(cont.)


V. Curbs


A curb is a steep raised element at the edge of roadway.

functions:

drainage control, roadway edge delineation,

right-of-way reduction, aesthetics,

delineation of pedestrian walkways,

reduction of maintenance operations, and

assistance in orderly roadside development.

high-speed rural highways: at the outside edge of the

shoulder

V. Curbs..(cont.)


Vertical curbs may range from 150 to 200 mm in height.

When the slope of the curb face is steeper than 1V:1H, and 1V:2H, the height should be limited to about 150 mm.

VI. Drainage Ditches


function of collecting and conveying surface water from

the highway right-of-way.

have adequate capacity for the design runoff

The depth of channel should be sufficient to remove

surface water without saturation of the subgrade

minimum desirable grade: drainage velocities needed to

avoid sedimentation

Generally, a broad, flat, rounded ditch section has been

found to be safer

VII. Sideslopes


The graded area immediately adjacent to the graded roadway shoulder.

Side slopes should be designed to insure the stability of the roadway and to provide a reasonable opportunity for recovery of an out-of-control vehicle.

Foreslopes : 1V:4H up to 1V:6H

Backslopes: 1V:6H to 1V:5H

VIII. Guardrails


A guardrail is provided where:

fills are over 2.4 m in height,

shoulder slopes are greater than 1V:4H,

there is sudden change in alignment,

great reduction in speed is necessary.

deep roadside ditches, steep banks,

right-of-way limitations,

Guardrails (roadside barriers) should be located beyond

the edge of the shoulder to ensure that the full shoulder

width may be used.

4. SIGHT DISTANCE


Sight distance is the length of highway visible to the

driver of a vehicle.

There are three different sight distances:

Stopping sight distance:

Passing sight distance

Decision sight distance

Intersection Sight Distance

to ensure safe and efficient operation of the road.

SIGHT DISTANCE..(cont.)


Criteria for Measuring Sight Distance

Sight distance is the distance along a roadway throughout

which an object of specified height is continuously visible

to the driver. This distance is dependent on the height of

the driver’s eye above the road surface, the specified

object height above the road surface, and the height and

lateral position of sight obstructions within the driver’s

line of sight.

Driver's eye height: 1.07 meters

Object height for stopping sight distance: 0.15 meters

Object height for passing sight distance: 1.30 meters

1. Stopping Sight Distance


Stopping sight distance is the minimum distance required

to stop a vehicle traveling near a design speed before it

reaches a stationary object in the vehicle’s path.

The minimum stopping is based on the sum of two

distances:

brake reaction distance

the distance traversed by the vehicle from the instant the driver sights

an object necessitating a stop to the instant the brakes are applied

braking distance

the distance needed to stop the vehicle from the instant brake

application begins

1. Stopping Sight Distance…(cont.)


In single lane roads, when two-way movement of traffic is permitted then stopping

sight distance should be equal to twice of the stopping distance plus 30 m safety

distance.

f=coefficient of friction

2. Passing Sight Distance


Passing Sight Distance is the minimum sight distance on two-way single roadway roads that must be available to enable the driver of one vehicle to pass another vehicle safely without interfering with the speed of an oncoming vehicle traveling at the design speed.

assumptions about driver behavior. The overtaken vehicle travels at uniform speed.

The passing vehicle has reduced speed and trails the overtaken vehicle as it enters a passing section.

When the passing section is reached, the passing driver needs a short period of time to perceive the clear passing section and to react to start his or her maneuver.

Passing is accomplished under what may be termed a delayed start and a hurried return in the face of opposing traffic. The passing vehicle accelerates during the maneuver, and its average speed during the occupancy of the left lane is 15 km/h [10 mph] higher than that of the overtaken vehicle.

When the passing vehicle returns to its lane, there is a suitable clearance length between it and an oncoming vehicle in the other lane.

2. Passing Sight Distance…(cont.)


40

The minimum passing sight distance for two-lane highways is determined as the sum of the following four distances, d1—Distance traversed during

perception and reaction time and during the initial acceleration to the point of encroachment on the left lane.

d2—Distance traveled while the passing vehicle occupies the left lane.

d3—Distance between the passing vehicle at the end of its maneuver and the opposing vehicle.

d4—Distance traversed by an opposing vehicle for two-thirds of the time the passing vehicle occupies the left lane, or 2/3 of d2 above





3. Decision Sight Distance


Decision sight distance is the distance needed for a driver to detect an unexpected or otherwise difficult-to-perceive information source or condition in a roadway environment then select an appropriate speed and path, and initiate and complete the maneuver safely and efficiently.

desirable to provide decision sight distance:

exit ramps,

diverging roadway terminals,

intersection stop bars,

changes in cross section,

Refer the table on your hand out

4. Intersection Sight Distance


5. HORIZONTAL ALIGNMENT


Horizontal alignment deals with the design of the directional transition of the highway in a horizontal plane.

Horizontal alignment includes the straight (tangent) sections of the roadway and circular curves that connect their change in direction

Why do we need horizontal curves: Terrain conditions, physical features, and right of way limitations

Depends: primarily on the design speed

type of curve,

friction,

super elevation and

widening of pavements on curves

Affects: safe vehicle operating speeds, sight distances, and opportunities for

phasing and highway capacity.

GENERAL CRITERIA


Horizontal alignment should meet these general considerations: Alignment should be as straight as possible within physical and economic

constraints. A flowing line that conforming generally to the contours is always preferable from construction, maintenance and aesthetic point of view to the one with long tangents that slashes through the terrain.

Alignment should be consistent. Try to avoid sharp curves at the ends of long tangents and sudden changes from gently to sharply curving alignment.

Curves with small deflection angle (5o degrees or less) should be at least 150m (500ft) long and increased 30m (100ft) for every one-degree in deflection angle, to avoid the appearance of kink.

Avoid horizontal curvature on bridges when possible, however, when curvature is unavoidable, place the entire bridge on a single curve as flat as physical conditions permit. Ending or beginning curve on or near a bridge can present design and construction problems with super elevation transition.

Avoid ―Brocken-back‖ – short tangent section between two curves in the same direction.

DESIGN ELEMENTS IN HORIZONTAL ALIGNMENT


I. Straight Line

provide the shortest distance between two established

control points

The following guidelines may apply concerning the length

of straights:-

Maximum length should not be greater than 20*Velocity (in

meter).

Minimum length should not greater than 2*Velocity for sight

distance.

In curves of the same direction intermediate straight lines

should be avoided or amounted to 6*Velocity.

DESIGN ELEMENTS IN HORIZONTAL ALIGNMENT..(cont.)


II. Horizontal Curves

four types of horizontal curves: Simple, Compound,

Reverse, Spiral Curve

A, Simple Curve: has a constant radius

NOTE: M-middle ordinate

T-Tangent length

C-Cord length

L-Length of curve

R-Radius of curve

∆-Central angle

PC-point of curvature

PT-Point of tangency

PI- Point of intersection



B, Compound Curves: consisting of a series of two or more simple curves of different radii turning in the same direction.

intersection curb radii, ramps and transitions into sharper curves.

the radii of the flatter curve should not be more than 50% greater than that of sharper curve

C, Reverse Curves: consists of two simple curves with equal or different radii turning in opposite directions.



D, Spiral Curves (Transition Curves): have got a radius of curvature gradually changing from infinity to the designed radius.

placed between tangents and circular curves or between two adjacent circular curves having substantially different radii.

Other type of curves: Brocken back, Switch back..

Reading assignment

Refer your surveying courses

SUPERELEVATION


Superelevation(e) is the raising of the outer edge of

the travel lane to counterbalances the centrifugal force,

or outward pull, of a vehicle traversing on the

horizontal curve.

To provide:

safely and comfortably navigating

through curves at higher speeds.

How?

by the side friction between the

vehicle tires and the surfacing

SUPERELEVATION..(cont.)


Analysis of superelevation:-

e

1

gR

Wv2

N

F

W





friction coefficients are dependent on:

vehicle speed, type, condition and texture of roadway surface,

weather conditions and type and condition of tires.

maximum rate of superelevation is controlled by four

factors:

climate conditions, terrain conditions, type of area and frequency of vey-

moving vehicles.

In summary

A rate of superelevation should not exceed 12%

A rate of 4 % or 6 % is applicable for urban design in areas with

little or no constraints.

As per ERA manual 4 % for urban and 8 % for rural.

SUPERLEVATION TRANSITION


superelevation should be introduced and removed uniformly over the length adequate for likely travel speeds.(comfort and safety)

Superlevaation transition section consists:

Superelevation runoff

tangent runout sections

Superelevation runoff: - is the length of highway needed to accomplish the change in cross-slope in the outside-lane (flat) to of fully superelevation.

Tangent runout: - consists of the length of the roadway needed to accomplish a change in outside-lane cross slope from the normal cross slope rate to zero (flat).


SUPERLEVATION TRANSITION..(cont.)





Minimum Length of Superelevation runoff:



Superelevation Runoff Location: On simple curves, 67 % of the Superelevation runoff normally is

developed on tangent and 33 % on circular curve.

AASHTO suggests a range of 60 % to 90 % of the runoff placed on the tangent is acceptable.

On spiral curves, the Superelevation runoff transition is

normally within the entire length of the spiral (TS to SC

and CS to ST)



Minimum Length of Tangent Runout

Methods of Attaining Superelevation


Four methods are used to transition the pavement to a

superelevated cross-section. These methods include

Revolving a travelled way with normal cross-slopes about the

centerline profile.

Revolving a traveled way with normal cross-slopes about the

inside-edge profile.

Revolving a travel way with normal cross-slope about the

outside-edge profile.

Revolving a straight cross-slope traveled way about the

outside-edge profile.


Methods of Attaining Superelevation…(cont.)

Methods of Attaining Superelevation…(cont.)


Axis of rotation with a Median


Case I: - the whole of the traveled way, including the median is superelevated as a plane section. The rotation in most cases is done about the centerline of the median. This method is used only for highways with narrow medians and moderate superelevation (specifically to width of 4 m or less)

Case II: - The median is held horizontal plane and two traveled ways are rotated separately around the median edges. This method is used mainly for pavements with median widths of 4 m and 18 m, although it can be used for any median.

Case III: - the two travelled ways are treated separately for runoff with a resulting variable difference in elevation at median edges. This design can be used with wide medians of 18 m or more.

Widening of Curves


As vehicle turns, the design vehicle occupies a greater width because the rear wheels generally track inside front wheels (offtracking) in negotiating curves.

drivers experience difficulty in steering their vehicles in the center of the lane.

Total widening is computed by adding the mechanical widening and psychological widening.

Widening of Curves…(cont.)


STOPPING SIGHT DISTANCE ON HORIZONTAL CURVES


Where there are sight obstructions (such as walls, cut

slopes, buildings, and longitudinal barriers) on the inside of

curves or the inside of the median lane on divided highways

make the appropriate adjustments to provide adequate sight

distance

Where sufficient stopping sight distance is not

available

(1) increase the offset to the obstruction,

(2) increase the radius,

(3) reduce the design speed.

SSD ON HORIZONTAL CURVES..(Cont.)


6. VERTICAL ALIGNMENT


Vertical alignment is composed of a series of straight-line gradients connected by curves, normally parabolic in form.

direct effect on the safety and comfort of the driver

Steep grades: slow down large, heavy vehicles in the uphill direction and stopping ability in the downhill direction.

Grades that are flat or nearly flat: pavement surface drains.

VERTICAL CURVES


Vertical curves are used to provide gradual change from one

tangent grade to another so that vehicles may run smoothly as

they traverse the highway.

VERTICAL CURVES…(cont.)

71

y = vertical distance from the tangent to the curve (meters)

x = horizontal distance from the start of the vertical curve (meters)

r = rate of change of grade per section (%)

Ex = elevation of a point on the curve


GRADES


the rate of rise or fall along the length of highway.

affected by the grades provided:

The cost of operation of vehicles, the speed of vehicles and the capacity of a highway

Maximum and minimum Gradients.

minimum gradient for the usual case 0.5%

Length of Crest Vertical Curves


Minimum length of crest vertical curves based on sight distance criteria, generally are satisfactory from the standpoint of safety, comfort and appearance.

Use:

When the height of eye and the height of

object are 1080mm and 600mm, respectively

Length of Crest Vertical Curves…(cont.)


Stopping Sight distance:

Use: the height of eye and

the height of object are

1080mm and 600mm,

respectively

Passing Sight Distance:

Use: the height of eye and

the height of object are

1080mm and 1080mm,

respectively

Length of Sag Vertical Curves


The selection of minimum length of a sag vertical curve is controlled by the following criteria: Headlight SSD

Passenger Comfort

Drainage Control

General appearance

A)Minimum length based on SSD (for Headlight SSD)

Length of Sag Vertical Curves..(cont.)


Sight Distance at Undercrossing:

Driver Comfort:

L=(V2A)/395

Length of Crest and Sag Vertical Curves Based on K factors

77

The reciprocal L/A is the

horizontal distance in meters

needed to make 1% change in

gradient

K = L/A

Where

K = limiting value, horizontal

distance required to achieve a 1%

change in grade

L = length of vertical curve (m)

A = Algebraic difference in

approach and exit grades (%)


Vertical Alignment Considerations


Vertical Alignment Considerations:

The profile should be smooth with gradual changes consistent

with the type of facility and the character of the surrounding

terrain.

A ―roller-coaster‖ or ―hidden dip‖ profile should be avoided.

Undulating grade lines involving substantial lengths of steeper

grades should be appraised for their effect on traffic operation,

since they may encourage excessive truck speeds.

Broken-back grade lines (two vertical curves—a pair of either

crest curves or sag curves—separated by a short tangent grade)

should generally be avoided.

7. PHASING OF HORIZONTAL AND VERTICAL ALIGNMENTS


implies their coordination so that the line of the road appears to a driver to flow smoothly, avoiding the creation of hazards and visual defects.

horizontal curves will be longer than vertical curves.

It is generally more pleasing to the driver when vertical curvature can be superimposed on horizontal curvature.

Sharp horizontal curves should not be introduced at or near the top of a pronounced crest vertical curve or at or near the low point of a pronounced sag vertical curve.

On two-lane roadways, long tangent sections (horizontal and vertical) are desirable to provide adequate passing sections.

Horizontal and vertical curves should be as flat as possible at intersections where sight distances along both roads and streets is important and vehicles may have to slow or stop.

THANK YOU


QUESTIONS?


Chapter Four:

EARTHWORK QUANTITIES AND MASS HAUL DIAGRAM



[email protected]

1. INTRODUCTION


Earthworks of highways include:

Earthwork activities.

Excavation(cut & fill)

Earthwork quantities and calculations.

Area of cross sections.

Determination of volume of earthworks by appropriate methods.

The mass‐haul diagram.

Determination of the planned movement of materials.

Calculation of the mean haul distance and the corresponding cost.

Earthwork activities. (Excavation)

3

Excavation of material from cutting and/or construction of embankments which is required to convert right of way from natural condition and configuration to a level that is ready for pavement works as prescribed in the design of the road.

The term earthwork(Excavation) includes:

Clearing and grubbing:

Removal of tress, strong roots…from area marked on the plan

Roadway and drainage excavation,:

Excavating and cording of roadway and ditches

Formation of embankment

Grading operation: road bed, shoulder, slopes, ditches

Excavation for structures:

Pipe or Concrete box culverts, foundation for bridge, retaining walls

Borrow excavation:

Excavation of quality material from borrow pits



Classification of Excavation:

Rock excavation material that cannot be excavated without blasting or the use of rippers

and all boulders or other detached stones.

Common excavation excavation and disposal of all materials of whatever character

encountered in the work, which are not classified as rock, borrow.

Borrow excavation excavation of approved material required for construction of

embankments.

Borrow: material not obtained from roadway excavation

Unsuitable excavation the removal and disposal of deposits of saturated or unsaturated

mixtures of soil and organic matter not suitable for embankment material

Waste: material excavated from roadway cuts but not required for making the embankment

Earthwork activities. (Excavation)….(cont.)

Earthwork activities. (Excavation) …(cont.)


equipment including: Modern grading operations shovels, scrapers, bulldozers, blade graders,

rollers, dragline excavators, motor trucks, tractors, etc.

Earthwork activities. (Excavation)…(cont.)


2. Earthwork Quantities


Area of Cross-Section:

(1) the graphical method and

(2) the coordinate method

(2)Area by Coordinate Method:

Simpler rule :

for area follows if we arrange in counterclockwise order the

coordinates in the form of fractions, the initial fraction (beginning at

any corner) being repeated to give a closed boundary.

Multiply along the marked diagonals and add the products (all positive);

multiply along the unmarked diagonals and add the products (all

negative). The difference gives the double area.

Earthwork Quantities…(cont.)


Trapezoidal Rule:

A trapezoidal rule assumes that if the interval b/n offset is

small, the boundary can be approximated to a straight line b/n

the offset.

A=L/2(O1+On+2(O2+O3+…..+On-1)

Simpson Rule:

This method assumes that instead of being made up of a series

of straight lines the boundary consists of a series of parabolic

area.

A=L/3(O1+On+4(∑even offset) +2(∑odd offset))

Earthwork Quantities…(cont.)


Volume of Earthwork The volume of earthwork may be found by means:

average end area

prismoidal formula.

Average End Area Formula Volume = V = ½ (A1 + A2)L

In which: A1 and A2 = area of end sections (m2)

L = length of solid(m)

This formula is applied to areas of any shape, but the results are slightly too large. The error is small if the sections do not change rapidly.

Prismoidal Formula. V = L/6 (A1 + 4Am + A2)

In which L is the distance between the two parallel bases A1 and A2 and Am is a section midway between the two end bases and parallel to them. Am is not an average of A1 and A2, but each of its linear dimensions is an average of the corresponding dimensions of A1 and A2.

SHRINKAGE AND SWELL


When earth is excavated and hauled to form an embankment, the freshly excavated material generally increases in volume. However, during the process of building the embankment it is compacted, so that the final volume is less than when in its original condition. This difference in volume is usually defined as “shrinkage”

When rock is excavated and placed in the embankment, the material will occupy a larger volume. This increase is called “ swell” and may amount to 30 percent or more.

SHRINKAGE AND SWELL…(cont.)


Materials %of

shrinkage/sw

ell

Light excavated soil

(ordinary earth)

10-20 .

Light excavated soil

(swampy ground)

20-40

Heavy excavated

soil

Up to 10

Excavated rock 5-25(swell)

3. MASS HAUL DIAGRAM


a curve in which the abscissas represent the stations of the survey and the ordinates represent the algebraic sum of excavation and embankment quantities from some point of beginning on the profile.

The steps involves:

End area calculations

Earthwork calculations

Preparation of mass haul diagram

Balancing earthworks using the mass haul diagram

A final stage of geometric design is then usually to make adjustments to the alignments in the interests of balancing or minimizing the earthwork quantities.

MASS HAUL DIAGRAM…(cont.)


Mass‐Haul Diagrams

A Mass Haul Diagram is a continuous curve representing the cumulative volume of earthwork along the linear profile of a roadway or airfield

Mass diagrams are extremely useful in determining the most economical distribution of material

Horizontal stationing is plotted along the x‐axis

Net earthwork values are plotted along the y‐axis

cumulative earthwork from the origin to that Point

upward sloping curves (rising left to right) indicate a cut

downward sloping curves (falling left to right) occur in a fill section

peaks indicate a change from cut to fill and

valleys occur when the earthwork changes from fill to cut



General steps to be following for determining mass haul diagram are:

1. Calculate fill and cut volumes separately

2. Correct the volumes calculated for swell and shrinkage

3. Tabulate the corrected cut and fill volumes, and aggregate volumes in the following format

4. Plot the Mass-haul diagram with stations in x-coordinate and

aggregate volumes in y-coordinate.



The mass haul diagram can be used to determine:

Proper distribution of excavated material

Amount and location of waste

Amount and location of borrow

Amount of overhaul in kilometer-cubic meters

Direction of haul.

Any horizontal line which joins points on the curve where balance is achieved is called a balance line.

A positive value at the end of the curve indicates that a waste operation will be the net result

A negative value at the end of the curve indicates that borrow is required to complete the fill



The following Figure shows a mass haul diagram curve with an accompanying profile of existing ground line and grade line.




Key terms associated with this process include:

Waste: material excavated from roadway cuts but not required for

making the embankment

Borrow: material not obtained from roadway excavation

Free Haul: excavated material may be transported without the

added cost above the unit bid price

Overhaul: excavated material transported to a distance beyond the

free haul distance

Economic Limit of Haul: distance which is more economical to

haul excavated material than to waste and borrow

The FHD and/or the limit of economic overhaul are

established and plotted on the mass haul diagram.

Balancing Earthwork Using the Mass Haul

Diagram

Balancing Earthwork Using the Mass Haul

Diagram


ECONOMICAL ANALYSIS


The economical limit of haul is defined as the distance

through which it is more economical to haul excavated

material than to waste and borrow.

E.L.H. = F.H. distance + Unit Price of Borrow

Unit Price of Overhaul

Where:

E.L.H= Economic limit of haul

F.H. = Free haul distance

USE OF MASS HAUL DIAGRAM


If mass curve is drawn for each trial grade it can be used

for selecting the most economical gradient which balance

the cut & fill.

Once the formation level is designed, it can be used to

indicate the most economical method of moving the earth

around the project and a good estimate of overall cost of

the earth work can be calculated.

The required volumes of material are known before

construction begins enabling suitable plant and machinery

to be chosen, site for spoil- hups and borrow pits to be

located and direction of haul to be established.

THANK YOU


QUESTIONS?


Chapter Five:

INTERSECTION AND TERMINALS



[email protected]

1

INTRODUCTION


An intersection is area where two or more highways join

or cross including the roadway and roadside facilities for

traffic movements within the area.

The efficiency, safety, speed, cost of operation, and capacity of

road infrastructures depend on the design of intersections.

A highway intersection is required to control conflicting and

merging streams of traffic so that delay is minimized.

This is achieved through choice of geometric parameters that

control and regulate the vehicle paths through the intersection.

Intersections vary in complexity from a simple intersection


Traffic maneuvers types:

INTRODUCTION


Basic elements that should be considered in the design of

intersections are:

Human factors, Physical elements and Environmental factors

Human factors

Driving habit

Ability of driver to make decision

Driver expectancy

Decision and reaction time

Conformance to natural paths of movement

Pedestrian use and habit

Bicycle traffic use and habit

INTRODUCTION


Physical elements

Vertical alignment at

intersection

Sight distance

Angle of intersection

Conflict area

Speed change lanes

Geometric design features

Traffic control devices

Lighting requirements

Safety features

Environmental factors

Cross walks

Economical factors

Initial, improvement and

operational costs

Effect of controlling or limiting

right of way on adjoining

residential or commercial

properties where

channelization restricts or

prohibits vehicular

movements

Energy consumption

INTRODUCTION


Intersections are generally classified into three general

categories:

At- grade intersections,

Grade-separated without ramps, and

Grade-separated with ramps (interchanges)

Selection of Junction Type

The choice of a intersection type requires knowledge of

traffic demand,

intersection performance and

accident prediction.

INTRODUCTION


INTRODUCTION


Basic advantages and disadvantages of different junction types, including grade separation, are as follows:

Priority (T-Junction, Cross-Junction).

For low flows: Can cause long delays.

Delays can be improved by signal installation.

Requires sufficient stopping sight distance.

Roundabouts.

For low to medium flows: Minimal delays at lower flows.

Shown to be safer than priority junctions.

Requires attention to pedestrian movements and accommodation of slow-moving traffic.

Grade-Separation.

For high flows: Results in minimal delays.

Expensive.

INTRODUCTION


INTRODUCTION


INTRODUCTION

At Grade Intersections


Most highways intersect at grade, and the intersection

area should be designed to provide adequately for turning

and crossing movements with due consideration to sight

distance, signs, and alignments.

The basic types of at-grade intersections are:

T,Y or three-leg intersection, which consist of three

approaches;

four-leg or cross intersections, which consist of four

approaches: and

multi-leg intersection, which consists of five or more

approaches.


At Grade Intersections

Grade separations and Interchanges


Intersection at grade can be eliminated by the use of

grade-separation structures that permit the cross flow of

traffic at different levels without interruption.

The advantage of such separation is the freedom from cross

interference with resultant saving of time and increase in safety

for traffic movements.

An interchange is a grade separation in which vehicles

moving in one direction of flow may transfer by the use

of connecting roadways.

These connecting roadways at interchanges are called ramps.





Grade-separated without ramps, and Grade-separated with ramps (commonly

known as interchanges)


Grade separations and interchanges may be warranted: As part of an express highway system designed to carry high volumes of traffic,

To eliminate bottlenecks,

To prevent accidents,

Where the topography is such that other types of design are not feasible,

Where the volumes to be catered for would require the design of an intersection at grade of unreasonable size, and

Where the road user benefit of reducing delays at an at- grade intersection exceeds the cost of the improvement.

The choice between these intersection types depends on: traffic,

economy,

safety,

aesthetics,

delay,

space requirements, etc.


Design Principles of At-Grade Intersections


Objectives in the design of at - grade intersections are to minimize delay and the number and severity of potential conflicts among different streams of traffic and between pedestrian and turning vehicles.

it is necessary to provide for the smooth flow of traffic across the intersection.

For example,

the corner radius of an intersection pavement or the radius required for design velocity of the turning roadway under consideration.

should ensure adequate pavement widths of turning roadways and approach sight distances.

intersections should not be located at or just beyond sharp crest vertical curves or at sharp horizontal curves.


The basic requirements of intersection design are

maximize safety and minimize traffic delay.

The design of the alignment including profiles, minimum radius

and widths of turning roadways,

The design of a suitable channeling system for the traffic

pattern,

The assurance that the sight distances are adequate for the

type of control at the intersection.



Alignment of At-Grade Intersections

The best alignment of an at-grade intersection is when

the intersecting roads meet at right or nearly right angles.

This alignment is superior to acute-angle alignments

because:

much less road area is required for turning at the intersection,

there is a lower exposure, time for vehicles crossing the main

traffic flow, and

visibility limitations, particularly for the trucks,





In designing the profile (vertical alignment) at the

intersection large changes in grade should be avoided;

preferably, grades should not be greater than 3 percent.

In any case, it is not advisable to use grades higher than 6

percent at intersections.

main factors governing the design of curves at at-angle

intersections.

The angle of turn,

the turning speed,

the design vehicle, and

traffic volume



ROUNDABOUTS

A roundabout is a one-way circulatory system around a central island, entry to which is controlled by markings and signs.

Priority is given to traffic already in the roundabout.

Roundabouts provide high capacity and minimal delay.

Roundabouts have a good safety record.





THE GENERAL LAYOUT

The general layout of a roundabout should provide for the following:

Adequate entry widths

Adequate circulation space compatible with entry widths

Central islands of diameter sufficient only to give drivers

guidance on the maneuvers expected.

Deflection of the traffic to the right on entry to promote movement and ensure low traffic speeds.

A simple and clear layout

Suitable visibility at any entry of each adjacent entry

Entry and exit deflection angles and central island radius should be adjusted to the design speeds



As shown in the figure below, five critical path radii must be checked for each approach.

R1 , the entry path radius, is the minimum radius on the fastest through path prior to the yield line.

R2 , the circulating path radius, is the minimum radius on the fastest through path around the central island.

R3 , the exit path radius, is the minimum radius on the fastest through path into the exit.

R4 , the left-turn path radius, is the minimum radius on the path of the conflicting left-turn movement.

R5 , the right-turn path radius, is the minimum radius on the fastest path of a right-turning vehicle





Channelistation of At-Grade Intersections

Channelization is the separation or regulation of conflicting traffic movements into definite paths of travel by traffic islands or pavement markings to facilitate the orderly movement of both vehicles and pedestrians. Proper channelization increases capacity, provides maximum convenience, and

instills driver confidence.

Channelization of intersections is considered for one or more of the following factors: Separation of conflicts

Control of angle of conflict

Reduction of excessive pavement areas

Regulation of traffic flow in the intersection area

Arrangements to favor a predominant turning movement protection of pedestrians

Protection of pedestrians

Protection and storage of turning and crossing vehicles

Location of traffic control devices





Sight distance at Intersections

Drivers on conflicting approaches must be able to see

other in time to assess whether an impeding hazard is

imposed and to take appropriate action to avoid an

accident.

Thus, sight distances must be analyzed to ensure that they

are sufficient for drivers to judge and avoid conflicts.

At-grade intersections either have:

no control

controlled by one of the following methods; yield control, stop

control, or signal control.






Traffic Controls


The purpose of traffic control is to assign the right of way to

drivers, and thus to facilitate highway safety be ensuring the

orderly and predictable movement of all traffic on highways,

control may be achieved by using traffic signals, signs, or markings

that regulate, guide, warn, and/or channel traffic.


The primary objective in the design of a traffic control

system at an intersection is to reduce the number of

significant conflict points.

Traffic Controls


Types of intersection control

Several methods of controlling streams of vehicles at

intersections are in use.

The choice of on of these methods depends on:

the type of intersection and the volume of traffic in each of

the conflicting streams.

types of intersection control are described below:

YIELD signs

STOP signs

Roundabouts

Traffic signals

Traffic Controls


YIELD signs: -

Yield signs are usually placed on minor road approaches; where it is necessary to yield the right of way to the major road traffic.

All drivers on approaches with yield signs are required to slow down and yield the right of way to all conflicting vehicles at the intersection.

Stopping at yield signs is not mandatory, but drivers are required to stop when necessary to avoid interfering with a traffic stream that has the right of way.

Traffic Controls


STOP signs: -

A stop sign is used where an approaching vehicle is required to stop before entering the intersection.

A stop sign may be used on a minor road when it intersects a major road, at an un-signalized intersection, and where a combination of high speed, restricted view and serious accidents indicates the necessity for such a control.

Stop signs should not be used at signalized intersections or on through roadways of expressways.

Traffic Controls


Roundabouts: -

A roundabout is a means of traffic control where one- way

traffic is circulating a round a central island priority with in the

roundabout is controlled by GIVEWAY(YIELD) signs for

entering traffic, although occasionally traffic signals may be

used.

It considerably reduces the number and severity of conflicts,

and makes the traffic flow self-regulatory and continuous,

reduces congestion, and promotes safety.

Traffic Controls

Traffic Signal

HU/Civil & Urban Engineering Dept. 38

One of the most effective ways of controlling traffic at an intersection.

can be used to eliminate many conflicts because different traffic streams can be assigned the use of the intersection at different times.

these results in a delay to vehicles in all streams, it is important that traffic signals be used only when necessary.

most important factor that determines the need for traffic signals:

Intersection‘s approach traffic volume and accident experience


The efficient operation of the signal requires proper timing design

The cycle length for an isolated intersection should be short, preferably between 35 and 60sec.

For very high volumes, cycle lengths should be kept below 120sec…(excessive delay)

Advantage:

Provide orderly movement, Reduce delay, reduce accidents, Increase capacity

Disadvantage;

Maintenance & monitoring, inefficient during off peak times, increase rear end collisions, signal break down

Traffic Signal…cont.


Type of traffic signals:

Fixed time signals:

Pre-timed signals are set to repeat regularly o cycle of red ,

yellow (amber) and green lights.

Vehicle actuated signals:

Signals in w/c the green periods vary and related to the actual

demands by traffic.

Semi-vehicle actuated signals:

The right of way rests with the main road and detectors are

located only on minor roads.





Definition of Some Terms:

Cycle Time (C): is the period of time required for one complete sequence of signal indication.

Yellow or amber or change interval (Yi): is time interval to alert motorists to the fact that the green light is about to change to red.

All rad time or clearance interval (ari or R): is time interval provided for the vehicle to cross the intersection and clear its back bumper, before the conflicting vehicle are given the Green.

Actual Green time (Gai): amount of time that vehicle are allowed to moving. Effective Green time (Gei): amount of time that vehicle are moving.

Rad time (Ri): amount of time that vehicle are should stop.

Phase: a part of the signal cycle allocated to a traffic movement





Yellow interval (Amber):

Where,

= the minimum yellow interval, (sec)

δ = perception-reaction time (sec)

W = width of intersection, (m)

L = length of vehicle, (m)

uo = speed (m/sec)

a = deceleration, (m/sec2)

G = grade of the approach road, and

g = acceleration due to gravity



Yellow intervals of 3 to 5 sec are normally used

When longer yellow intervals than 5 sec are computed

from the above equations,

an all-red phase can be inserted to follow the yellow indication,

but the change interval, yellow plus all-red, must be at least the

value computer from the equations.



Cycle lengths: -

one complete sequence of signal indication

(Webster method )is presented here.

Where, Co = optimum cycle length (sec)

L = total lost time per cycle (sec)

Vij = flow on lane j having the right of way during phase i

Sj = saturation flow on lane i.

Yi = maximum value of the ratios of approach flows to saturation flows for all traffic streams using phase i (i.e., Vij/ Sj)

n = number of phases

Sj is maximum rate of discharge is the saturation flow( 100% green time.



Total Lost Time:

some time is lost before the vehicles start moving

Where, Li = lost time for phase i

Gai = actual green time for phase i

Yi = yellow time for phase i

Gei = effective green time for phase i

Where: R is the total all-red time during the cycle



Allocation of green times:

In general, the total effective green time available per

cycle is given by:

Where,

C = actual cycle length used (usually obtained by rounding off

C0, to the nearest 5 sec)

Gte=total effective green time per cycle.

the effective green time for each phase.



And the actual green time for each phase is obtained as:

Example:


Terminals


Terminals can be: Parking or Truck terminals

Parking facilities:

Widespread parking problems exist in business districts and other highly developed areas.

The geometric design of parking facilities mainly involves the dimension and arranging of parking bays to provide:

safe and easy across without seriously restricting the flow of traffic on the adjacent traveling lanes.

Truck terminals:

The planning and design of facilities to accommodate the loading, unloading, and parking of trucks can have a significant impact on the operational efficiency of the street and highway system

Terminals


Types of parking facilities

On street and off street

On-street parking Facilities:

Parking bays are provided alongside the curb on one or both sides of the street.

Unrestricted parking: duration of parking is unlimited and parking is free

Restricted parking: limited to specific times of the day for the max duration and may be free or not.

Off-street Parking Facilities:

These facilities may be privately or publicly owned.

Include surface lots and garages

Self or attendant parking


Terminals

Different types on-street parking layout


Different types off-street parking layout

Terminals

Thank You!


QUESTIONS?

54

Documents

Highway-I Lecture Slide