Design & Appraisal

• Basic Access  
• Least-Cost Design
• Participatory Selection Process
• Screening and Ranking Methods
• Economic Appraisal Methodologies
• Economic Aspects of Low Volume Roads
• Key Readings

The design and appraisal of rural transport infrastructure needs to consider (i) the nature of accessibility, and (ii) design solutions for motorized and non-motorized means of transport. Issues of participation and the selection process need also to be considered 

KEY ISSUES 

1. Basic access is one of the necessary conditions for the alleviation of poverty in rural areas of developing countries, at par with the provision of other "merit goods" such as basic health and basic education services. "Basic access" is defined as both (i) the availability of all-weather road access from villages to the main road network, and (ii) reliable access to basic social and economic services on the intra- or near village track and path network on which trips are made mainly on foot or by non-motorized means of transport. In cases of rugged terrain, low affordability, and low provision of motorized transport services basic access might mean all-season access only by non-motorized means of transport.

2. Least-Cost Design

   In order to provide as many poor rural dwellers as possible with basic access, and in view of the limited institutional and financial resources available for investments and upkeep of these networks, and furthermore considering the low (motorized) traffic levels, it is necessary to apply "least-cost" design approaches, that is minimizing total life-cycle costs for investment and maintenance. In most cases this will mean single-lane, simple design standard and spot-improved gravel and earth roads for the access to the villages, appropriate for the use of the prevailing rural transport vehicles, including non-motorized means of transport, allowing all-season access, but permitting interruptions during severe weather, and improved paths and provision of footbridges for the intra- and near village transport network.

3. Participatory Selection Process

   In order to create the local ownership necessary for sustainability, the planning and appraisal process for rural transport infrastructure must necessarily be participative. Planning and appraisal tools must be designed and applied jointly with responsible local government planners and/or the local communities. One of the key tools for the participatory process is the preparation of a District/Local Government Transport Master Plan.

4. Screening and Ranking Methods

   Selection is proposed to be a two-step process: first screening and second ranking. Screening based on poverty criteria might be necessary to single out poverty areas where access is particularly poor and incomes low. Ranking of possible alternatives is necessary in view of limited budgets.

5. Economic Appraisal Methodolgies

   For low volume roads (particularly for traffic levels below 50 vehicles per day) it is suggested that cost-effectiveness criteria (in particular, total life-cycle cost of investment per populations served) should be used to rank investments in rural transport infrastructure, under the condition that least-cost design methods have been applied and the main objective of the intervention is poverty alleviation. In case of rather economic investment objectives, such as the upgrading of an existing basic access road to a fully engineered road, or the provision of an alternative, shorter access to a village, cost-benefit approaches appropriate for low volume roads are presented and discussed in this paper. It is suggested that the provision of basic access to communities with no or unreliable access (up to a certain cost per capita) should have priority over investments into upgrading of existing basic access roads to a higher standard.

   For intermediate levels of traffic (between about 50 to 200 vehicles per day) an appropriate economic appraisal tool is the Road Economic Decision Model, see paragraph 6 below.
   
   
6. Economic Aspects of Low Volume Roads

   To manage a network of low volume roads on a rational manner, many issues need to be addressed such as economic, engineering, social, environmental, financial, equity, institutional and political aspects. Decision-makers should evaluate these aspects to formulate a coherent work program that maximizes overall benefits to society.

   Under certain circumstances, road maintenance and road improvement expenditures are economically justified. To help road agencies identify economically justified road works, an economic evaluation is done, which measures the worth of the investments to 'the economy', that is to the country. The resources that a country, or its roads agency, have for such works are nearly always insufficient for the total needs, and an economic evaluation is a critical step in the process of determining the optimal allocation of the available resources, in other words, which of the proposed projects should qualify for the available funding, and what is their priority and the optimal timing for the work.

   Rural Transport Infrastructure Note RT-3, "Paving of Unpaved Roads: Economically-Justified Paving Costs", presents an overview of the economic evaluation of low volume roads and typical scenarios in which paving may be examined as a valid investment option. A detailed economic evaluation of road investments and maintenance options can be done using a road investment model such as:

   • the Highway Design and Maintenance Standards Model (HDM-III), which estimates the deterioration of paved and unpaved roads, over time, and the resulting road user costs and economic evaluation, or
   • the Roads Economic Decision Model (RED), which is customized to address some of the specific characteristics of low volume roads such as: a) the high degree of uncertainty of the inputs, b) periods during a year with disrupted passability, c) levels of service and corresponding road user costs defined not only by roughness but also by speeds and passability; d) high potential to influence economic development; and beneficiaries other than motorized road users.

   The economists and their models view cost savings as benefits; for example if the costs to the road users (the truckers etc.,) would be less on a paved road than they would be on an unpaved road, then the difference would be economic benefits. Road user costs typically include:

   • fuel and tires cost
   • maintenance labor and parts costs
   • depreciation and interest costs
   • the passengers' time costs, and
   • the inventory cost of the cargo while it is in transit.

   World Bank Technical Paper 234 "Estimating Vehicle Operating Costs," describes road user costs calculations and presents a model (HDM-VOC) that estimates vehicle operating costs, using the HDM-III relationships, for ten vehicle types as a function of the vehicle characteristics, utilization and unit costs, and road geometry and roughness.

   Roughness is the irregularity of the road surface and affects the dynamics of moving vehicles, increasing the wear on vehicle parts and the handling of a vehicle, and so having an appreciable impact on vehicle operating costs, the economic evaluation of road maintenance and upgrading expenditures, and the safety, comfort and speed of travel. Roughness is measured using the International Roughness Index (IRI) which is a mathematically defined summary statistic of the longitudinal profile in the wheelpaths of a traveled road surface. The UMTRI Road Roughness Home Page by the University of Michigan Transportation Research Institute contains information about road roughness measurements and analysis intented for engineers.

   On unpaved roads, roughness varies over a year as a function of the season, the changing location of the wheelpaths chosen by the vehicles, and the number and the effects of gradings and other maintenance activities. Therefore, a roughness measurement at a given point in time is not sufficient to characterize the average annual roughness of unpaved roads. Also, due to the fragility of various roughness measurement apparatus, these are usually not deployed on unpaved roads forcing road agencies to define the average annual road roughness of unpaved roads by other means. Rural Transport Infrastructure Note RT-1, "Typical Unpaved Roads: Roughness Predicted By the HDM-III Model", presents examples of HDM-III roughness predictions for a lateritic gravel road and for an earth road, and may be used more generally as a guide for the estimation of roughness of unpaved roads. Rural Transport Infrastructure Note RT-2, "Unpaved Roads: Roughness Estimation By Subjective Evaluation", presents two approaches to subjective estimation of roughness of unpaved roads, both based on the World Bank's work in the development of the Highway Design and Maintenance Standards Model, HDM-III, and the Highway Development and Management Model, HDM-4. The deterioration of unpaved roads Model DETOUR implements in MS-Excel the road deterioration relationships of unpaved roads of the HDM models.

KEY READINGS