Impact Evaluation of Transport Interventions by Raitzer David A.;Blöndal Nina;Sibal Jasmin;

Author:Raitzer, David A.;Blöndal, Nina;Sibal, Jasmin;
Language: eng
Format: epub
Publisher: Asian Development Bank Institute
Published: 2019-08-15T00:00:00+00:00

8. Evidence Gaps

The relatively limited number of studies to date for many transport interventions suggest that there are large gaps in evidence for the sector. As most of the evidence available concerns rural roads, the gaps are greatest for urban and large interventions.

Coverage gaps

• Urban transport: There is a body of research emerging on urban transport policy measures, such as driving restrictions, but the body of research on urban infrastructure is mostly limited to a few studies in the PRC; Taipei,China; India; and Mexico. Although ADB and other development actors are moving increasingly toward investment in urban transport and focusing more on environmental outcomes, existing studies mostly evaluate roads and rural roads in particular. This is partly because concerted financing of urban transport has grown more recently than other investments such as roads, and it may be in part due to the small-n problems of evaluating urban transport facilities.

• Non-road transport: Most impact evaluations focus on roads, especially rural roads, so that the evidence on projects related to rail, urban mass transit, and sea or air travel is far more limited. There is a nascent body of work emerging on metros, bus rapid transit, buses, and other transit forms. A few ongoing and recent studies include an experimental component to explore complementary interventions, such as subsidies to fares or information nudges to shift to ridership. However, the absolute number of studies remains limited.

• Complementary interventions: Achieving sustainable road safety and reductions in morbidity and mortality from road accidents is increasingly recognized as important, but this all depends on achieving behavioral change. Only a relatively small number of studies have assessed this. Box 4 outlines some examples that illustrate how road safety can be explored further through impact evaluation. Similarly, measures to address gender disparities in transport or enhance female safety and ridership have had little attention.

• Behavioral and efficiency-enhancing measures are central to the avoid–shift–improve approach that guides much urban transport development. These include congestion-reducing measures such as pricing, incentives for modal shifts, and enhanced traffic demand management. Few of these mechanisms have been tested.

• Improvements to logistics, ports, and trade facilitation have not often been subjected to impact evaluation. There is little evidence on airports, seaports, border facilities, or other infrastructure investments, nor on trade and logistic-related policy reforms.

• Operation and maintenance is considered a widespread challenge for infrastructure projects, including in transport. None of the identified studies explore the impact of different maintenance funding or contracting systems. The study of auditing mechanisms shown in Box 5 provides an example of how this might be done. Similarly, there is little evidence on the effects of engaging local communities or specific subgroups (such as women) in either construction or maintenance.

Outcome gaps

Only a subset of outcomes represented in the theory of change presented in this report have been assessed.

• Effects on infrastructure quality are not frequently evaluated. At the basic level of outputs, there can be differences in how mechanisms underlying the causal chain, such as different contractual mechanisms, affect longevity and functionality of the transport infrastructure constructed.

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