An Underrated Development Investment That Can Double Returns: Trail Bridges

ATAI-affiliated researchers Kevin Donovan (Yale) and Wyatt Brooks (Arizona State) conducted a randomized evaluation of a trail bridge construction program in Rwanda implemented by Fika (formerly Bridges to Prosperity).

Ireme is a smallholder farmer in rural Rwanda. To reach the nearest market, she and her neighbors once had to choose between an hours-long detour or a treacherous crossing that few were willing to risk. Recently, a new trail bridge changed everything, and she has started growing higher-value crops to take advantage of the reliable, direct route to additional farm plots that she can tend for a larger harvest. For Ireme’s family, the benefits are both immediate and lasting. They now have better access to healthcare and education, and with her business growing, their future looks more secure too.

Ireme’s experience is one of nearly 400,000 Rwandan households that have benefited from trail bridges built by Fika, a nonprofit organization that addresses rural isolation through building reliable infrastructure. Beyond providing basic access to transportation infrastructure, do trail bridges have an economic impact for the households they serve? A new randomized evaluation of Fika’s Rwanda program offers the most rigorous evidence to date on the economic returns to rural transport infrastructure.

The Problem

Why evaluate infrastructure?

Ensuring rural communities have access to dependable transit systems could transform how the individuals most vulnerable to economic shocks and climate change access essential services, pursue economic opportunities, and travel safely from place to place. Yet, the availability and reliability of transit networks are starkly uneven across the globe, particularly in rural areas. One report estimates that high-income countries have over twice the density of road kilometers, on average, when compared to low- and lower-middle income countries. Rigorous research is an essential tool for understanding which transport infrastructure investments deliver the greatest returns relative to their costs, and why. Because infrastructure projects are typically financed through national governments and international donors, understanding the broader effects of these interventions can support more thoughtful, evidence-informed policy decisions.

Trail bridges offer a particularly compelling case study. Unlike major road construction, trail bridges are low-cost, fast to build, and targeted at specific bottlenecks where a water crossing may be the only obstacle between a community and the land, services, and markets it needs. Rwanda’s Western, Northern, and Southern provinces are extremely rugged, with terrace farming and mountainous topography. Rivers and ravines cut between hills, and in many communities attempting to cross without a bridge is simply too dangerous and costly to be practical. Fika, formerly known as Bridges to Prosperity, has built hundreds of bridges across Rwanda, in partnership with the national government and local districts. To rigorously quantify the impact of those bridges on the households they serve, Fika partnered with academic researchers to conduct a large-scale randomized evaluation.

The Research

Introducing the RCT: Design

To answer this question, Fika partnered with ATAI-affiliated researchers Kevin Donovan and Wyatt Brooks to conduct what may be the first-of-its-kind randomized evaluation of transportation infrastructure at scale. Fika had identified over a thousand bridge sites across rural Rwanda that were ready for construction, but could not build all of them at once. Researchers worked with Fika to randomize the order in which a sample of those bridges would be built across a three-year period from 2021 to 2024. The study employed a stepped-wedge design that mitigated the tricky ethics of an RCT: villages that had not yet received a bridge served as the comparison group for villages that had.

At each of the 97 sites, researchers identified villages on both sides of the river near the bridge and conducted household-level surveys. Household surveys were conducted in four waves, one before any bridges were built and three more annually as construction proceeded. In total, the team surveyed approximately 10,000 households across 290 villages over four years, tracking income and consumption, farming activity, land use, and broader measures of wellbeing.

Bridge sites were selected by Fika and the Rwandan government through a comprehensive needs assessment that considered local population, distance to services, difficulty of crossing, and the availability of alternatives. On average, Fika estimates that between 2,869 and 3,938 households directly benefit from each bridge. As the results show, the number of direct beneficiaries turns out to be central to understanding how bridges impact local economies. 

The Results

By the second year after a bridge was constructed, households in program villages experienced meaningful improvements across multiple dimensions of economic wellbeing. Notably, overall household consumption rose, driven by increased market purchases rather than consumption of own farm output, suggesting bridges expanded households’ ability to buy and sell in local markets. Harvests, farm profits, and the adoption of cash crops all increased, indicating a broad shift toward more commercially oriented farming.

Bridges unlock land access, particularly for smaller farmers

These gains were concentrated among households on the more densely populated side of the river, who also used more fertilizer and reported income increases. Farmers who lived on the densely populated side, where land per household was scarcer, became more likely to cross to farm, traveled further to reach further fields, and cultivated more land overall after bridges were built. These gains disproportionately benefit smaller farmers, who were most constrained by the lack of accessible land to begin with and saw the largest increases in cultivated area and harvests once a bridge opened up new farming territory across the river.

Bridges deliver nearly double return on investment

Each bridge in the study cost approximately US$100,000, substantial by the standards of most development interventions but modest compared to large-scale infrastructure like roads or electricity grids, and downright cheap when framed in terms of the cost-per-beneficiary. To assess cost-effectiveness, the research team compared the cost of each bridge against the economic gains households experienced over the bridge’s estimated 40-year lifespan. Even using a conservative approach, the researchers found that the economic gains to households over the 40-year life of each bridge nearly doubled the original cost of building it with a rate of return between 78 to 98 percent.

The same bridge that unlocks a new field also connects a child to school, a patient to a clinic, and a family to the broader economic life of their region. The research team is currently analyzing survey data on healthcare and education outcomes, with findings forthcoming.