Upload
homer-blair
View
225
Download
0
Tags:
Embed Size (px)
Citation preview
Feeder Road Prioritization
Engineering Issues
G2a Cost Estimation SurveyG2b Road Condition Survey
John Hine / Simon Done
November 2000
G2a G2bCost Estimation Survey Road Condition Survey
Access Roughness
Access Category A Traffickability
Access Category B Passability
Access Category C Roughness Key
Spot Improvements Traffickability Key
Full Rehabilitation Passability Key
Problems with Spot Imp’ments Effects of imp’ments
Cost Est. Survey vs. MPBS Survey Procedure
Survey Procedure
Consistency is required
Typical Results
Accessibility Strip Map
Calculation of catchment areas
Cost Estimation SurveyAccess
The priority is on arriving at the destination rather than doing so quickly or smoothly.
Access permits maximum benefit at minimum cost.
Access should be reliable if farmers are to plant surplus crops and traders are to buy and operate vehicles.
Access is more appropriate for short roads (20 km?) than for long roads (100 km?), and for low traffic than high traffic.
Access should be provided for all vehicle types that may use the road.
Access should be year round (rather than seasonal), except perhaps for closures of up to a day or two.
The biggest threat to access is rainfall and runoff.
Cost Estimation Survey
Access Category A
Sites where, for local vehicle types:Year round access is impossible even if in an emergencyRoad users are in danger of injuryThe road is under water for time periods of more than two consecutive days
Improvement of Category A sites will provide emergency access in the short term
Cost Estimation Survey
Access Category B
Sites where, for local vehicle types:Year round access is possible, but unreliableAccess is likely to be lost in the near futureRoad condition is likely to deteriorate as each vehicle passesRoad condition is likely to deteriorate as each rainstorm passesThe road is badly erodedMotor vehicle speed is reduced to below normal walking speedCyclists are forced to dismountVehicles are liable to damage as they pass
Improvement of Category A & B sites, with maintenance, will provide reliable year round access in the long term. This level of improvement may be termed spot improvements.
Cost Estimation Survey
Access Category C
Sites where, for local vehicle types:Year round access is possible, and reliableRoad condition is stableDeterioration is unlikely in the near future under existing conditionsSurface roughness is not enough to slow motor vehicles to below walking speed
Improvement of Category A, B & C sites will maintain access and permit smooth, comfortable travel. This level of improvement may be termed full rehabilitation
Cost Estimation Survey
Spot (Accessibility) improvements
This refers to the improvement of localised sites where access is:•lost,•unreliable,•at risk in the near future, or•dangerous,
but leaving those lengths of road where vehicles can pass safely and reliably all year round.
The appearance of the road may be variable, but the quality of work carried out is high, and the work should be robust.
Spot improvements may be appropriate for the involvement of local communities.
Cost Estimation Survey
Full rehabilitation
This refers to the improvement of the entire road such that access is safe and reliable all year round, and also that a smooth, often gravelled, surface permits comfortable travel along the whole length
Cost Estimation Survey
Problems with Spot improvements
Can be unacceptable to:•Politicians•Road Authorities•Travelling public•Tax paying electorate•Road contractors
But:
A cost effective way of providing access to many people at minimum cost.
Cost Estimation Survey
Cost Estimation Survey MPBS
One-off improvement cost Repeated maintenance cost
Makes a road maintainable Keeps a road maintainable
Fast and approximate Detailed and accurate
Used for Prioritization Used for letting contracts
Estimates required activities Schedules actual activities
Condition allocated to sections Condition allocated to road
All possible improvement works Only periodic and routine m’t
Groups activities together Keeps activities separate
Simplifies to 17 activities Requires 34 separate activities
Unit costs are approximate Unit costs are exact
Spot imp. & rehabilitation costs Rehabilitation cost only
Limited decision flexibility Great decision flexibility
Cost Estimation Survey
Survey Procedure
Survey during the rains if possible
Divide the entire road into sections
Identify the problem type for each section
Identify the vehicle types likely to use the road
Record the Access Category of each section
Estimate required quantities to treat the problem
Transfer the unit cost for each treatment
Calculate the total cost for each Access Category
Calculate the costs of emergency access, spot improvements and full rehabilitation
Incorporate costs into the Prioritization procedure
Cost Estimation Survey
Consistency is required during survey
•Dividing a road into sections
•Recording the Access Category
•Recording the Problem Type
•Estimating required quantities
Cost Estimation Survey
Typical results - a road of 5.26 km
Full rehabilitation (Cat A+B+C)
$52,081 100%
Spot Improvements (Cat A+B)
$15,909 30%
Emergency Access (Cat A)
$4,067 8%
Cost Estimation Survey
Accessibility Strip Map
Used to record:•junctions•sites where access is lost•sites where access is difficult
In order to assess the social impact of:•existing road condition•expected road condition
On the affected population
Cost Estimation Survey
Calculation of catchment areas
Identify all water crossings - GPS, landmarks, etc
Locate the crossing on map - 1:50,000
Measure catchment size
Use catchment size to estimate cost of structure
Road Condition SurveyRoughness – Definition
This refers to the surface condition of the road. Definitions of four roughness levels are suggested, and it is possible to correlate each level to an IRI value, or the comfortable travel speed of a vehicle, although the latter requires careful calibration.
Roughness is recorded by:
•Direct assessment of IRI•Correlation with description - ‘good gravel’, ‘average’,
‘poor’, ‘extremely poor’•Roughness Key - based on correlation with
comfortable travel speed
Road Condition Survey
Traffickability – Definition
This refers to factors that significantly reduce traffic volumes (but do not absolutely prevent movement) such as poor road condition in the wet season or, on occasion, extreme roughness. E.g. a road may be said to have traffickability problems if, at some point in the year, the wet season traffic is less than 50% of the dry season traffic.
Traffickability is recorded by:
Assessment of length and duration of traffickability problems•Traffickability Key - based on correlation with the
proportion of the road of Category A or B
Passability – Definition
This refers to the inability of vehicles to travel along the road on grounds of poor road condition. A road is said to have passability problems if, for a period of at least two days at some point in the year, a vehicle which would normally use the road is unable to pass.
Passability is recorded by:
•Assessment of duration of passability problems•Passability Key - based on correlation with the
Cat. A water crossing of greatest cross section
(or length of carriageway of Cat. A)
Road Condition Survey
Roughness Key
This refers to the surface condition of the road. Definitions of four roughness levels are suggested, and it is possible to correlate each level to an IRI value, or the comfortable travel speed of a vehicle, although the latter requires careful calibration.
Description IRI Speed (kph)
G – Good gravel 6 > 60
A – Average 9 40 – 60
P – Poor 12 20 – 40
E – Extremely poor 17 < 20
Road Condition Survey
Traffickability Key
The Traffickability Key is based on the assumption that a single, isolated, difficult site will not in itself cause traffic levels to drop, but that as the total length of road where access is difficult increases, more traffic will be dissuaded from travelling and the duration of problems will extend. Thus the percentage of the road length which is of Category A or B is used to estimate the duration of the problems.
L(A+B) / Ltotal (%) Duration of traffickability problems (months)
0 – 10 0
10 – 30 0.25 x Rainy season
30 – 50 0.50 x Rainy season
> 50 0.75 x Rainy season
Road Condition Survey
Passability Key
The Passability Key is based on the assumption that closure of a road depends on a single site, rather than an accumulation of sites in the Traffickability Key. Only Category A sites are considered, since the definition of this Category is the loss of access.
Sites of Category A Duration of passability
Channel XS Area problems (months)
0 – 1 m2 0.25 x Rainy season
1 – 3 0.50 x Rainy
3 – 10 0.75 x Rainy
> 10 1.0 x Rainy season
Any rain related carriageway
problem of Cat. A 0.50 x Rainy season
Road Condition Survey
Effects of improvements on Road Condition
The improvement works have the following effect upon:
Improvements are
made to sites ofAccess Category: Roughness Traffickability Passability
Category A Remains rough Problems remain Problems remain
Category A & B (spot improvements) Remains rough, Problems solved Problems solved
but may reduce
somewhat
Category A, B & C (full rehabilitation) Smooth Problems solved Problems solved
Road Condition Survey
Road Condition Survey
Survey Procedure
Assess existing overall roughness, passability and traffickability of the road - by interview, direct observation, or using ‘Keys’
Assess expected overall roughness, passability and traffickability after the road has been improved to a Spot Improvement or a fully rehabilitated standard. Guidance is provided for this assessment
Incorporate existing and expected conditions into the Prioritization Index