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Study Overview

The social costs and benefits of infrastructure construction: Air pollution and bus rapid transit (BRT) in Dakar
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Infrastructure is a crucial determinant of economic growth and productivity, and public transport infrastructure increases access to labor markets, educational opportunities, and other services. Public transport projects are often touted for improvements in air quality, but negative externalities, such as high air pollution during the construction phase, are rarely measured or included in the cost-benefit analysis that drives decision making. Further, the social costs and benefits of infrastructure projects depend crucially on usage and modal shifts once the project is completed.  This impact evaluation (IE) aims to be the first in the context of Senegal to comprehensively study the impact of a Bus Rapid Transit (BRT) on ambient air pollution levels across all phases of the infrastructure project. We will use the launch of a new BRT being constructed in Dakar, Senegal, to measure the impacts during its construction and operational phases. This impact evaluation will help to provide insights into the underexplored area of the social costs and benefits of infrastructure construction and operation. 


Registration Citation:

Milusheva, S., Hoffmann B. (2021).The social costs and benefits of infrastructure construction: Air pollution and bus rapid transit (BRT) in Dakar

Environment and Disaster Management
Health, Nutrition, and Population
Urban Development
Additional Keywords:
Air quality, pollution, public transit, bus rapid transit
Secondary ID Number(s):

Principal Investigator(s)

Name of First PI:
Sveta Milusheva
World Bank
Name of Second PI:
Bridget Hoffmann
Inter-American Development Bank

Study Sponsor

Study Sponsor Location:
United Kingdom

Research Partner

Name of Partner Institution:
Type of Organization:
Government agency (eg., statistics office, Ministry of Health)

Intervention Overview


The main intervention of interest is the construction of the Bus Rapid Transit (BRT) system, which aims to increase urban mobility within the Greater Dakar Area. Construction of the BRT is foreseen to take around 30 months. The BRT will initially operate along an 18.3 km corridor starting from Guediewaye, in the northern suburb of the capital city, to Place Cabral, in the Petersen area of the city center. The BRT route crosses 2 administrative departments and 14 municipalities. The municipalities crossed by the BRT were home to almost 1,000,000 inhabitants in 2017, about 33% of the total population of the Greater Dakar Area. The new bus will have 23 stops and 3 exchange hubs, one at each terminus and another one in the commune of Grand Medine, close to the existing road hub of the road to the airport and other major roads of the city’s network. The BRT will have its own lanes, separated from the other vehicles to avoid traffic, but there will be parallel lanes on each side to still allow other vehicles to use the roads, sidewalks for pedestrians and cycle path on some portions of the corridor. The 144 BRT buses will be able to carry 150 passengers each; they will operate between 6 am and 10 pm every day. The BRT is expected to carry an average of 320,000 passengers daily when in operation, and for public transport users, the journey time is expected to be reduced from 95 to 45 minutes. The BRT aims to improve the connectivity of the local population and to reduce congestion once fully operational.

Theory of Change:

The Bus Rapid Transit (BRT) intervention is divided into two phases: the construction and then the operation. This new public transport system will affect the mobility choices and living environment of the population, particularly the quality of the air they breathe and their exposure to air pollution. The causal links on how the BRT will affect different aspects of people’s daily lives are described below:

First, the construction phase is expected to temporarily reduce urban mobility and increase the population’s exposure to air pollution. The construction phase will likely reduce urban mobility by monopolizing the use of roads normally used for traffic in densely populated neighborhoods. The reduction in the number of traffic lanes will lead to a greater concentration of traffic on the other roads, which is expected to increase congestion and travel times, leading to higher vehicle exhaust emission and air pollution. The construction itself generates dust and will likely contribute to higher levels of ambient air pollution in the areas surrounding the construction sites.

In the second phase, once the BRT is in operation, users will have a fast, reliable, safe, and comfortable means of transport, and these comparative advantages could therefore give rise to a modal shift towards the BRT.  In the medium term, this could reduce traffic congestion and ambient air pollution, leading to positive health impacts. If, however, modal shift does not occur, travel times and congestion would increase due to the reduction in the number of lanes, one of which is occupied by the BRT. The effect of the BRT operationalization would then be the opposite, with higher traffic congestion, increased air pollution, and longer travel time, resulting in worse long-term outcomes.

Multiple Treatment Arms Evaluated?

Implementing Agency

Name of Organization:
Type of Organization:
Public Sector, e.g. Government Agency or Ministry

Program Funder

Name of Organization:
World Bank
Type of Organization:
Foreign or Multilateral Aid Agency

Intervention Timing

Intervention or Program Started at time of Registration?
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Evaluation Method

Evaluation Method Overview

Primary (or First) Evaluation Method:
Difference in difference/fixed effects
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Method Details

Details of Evaluation Approach:

We will estimate the impact of the BRT on air quality during the construction phase by using two difference-in-difference designs. The first uses segments of the BRT route currently under construction as the treatment and uses segments of the BRT route that will be constructed later as the control. Air quality in treatment and control segments will be measured using air quality monitors approximately 1 km or less from the BRT route. The second one uses monitors within 1km of the BRT line as the treatment and uses those located between 10km and 30 km from the BRT route as the control monitors.

We will estimate the impact of the BRT on air quality during operation using a difference in difference strategy, where the pre-construction time period will be used as the “before” period and monitors located 10-30km from the BRT route will be used as the control group.

Outcomes (Endpoints):

Primary: Ambient air pollution levels

Secondary: Air pollution exposure, Congestion

Unit of Analysis:
Air pollution at the hourly level

The key hypothesis we would like to test is  whether and to what extent the construction and operation of an urban BRT affects ambient air pollution levels.

Unit of Intervention or Assignment:
hourly entry per monitor
Number of Clusters in Sample:
Number of Individuals in Sample:
610848 hourly observations across all monitors
Size of Treatment, Control, or Comparison Subsamples:
7272 hourly entries per monitors per treatment arm

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Outcomes Data

Data system for air quality data from a network of low-cost mobile monitors and ground monitoring stations.
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Treatment Assignment Data

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Data Analysis

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Study Materials

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Registration Category

Registration Category:
Prospective, Category 1: Data for measuring impacts have not been collected

Completion Overview

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Preliminary Report:
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Data Availability

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Other Materials

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Study Stopped