Feeder Road Prioritization Engineering Issues G2a Cost Estimation Survey G2b Road Condition Survey...

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