The impact of short-term driving restrictions on mobility and traffic congestion in Delhi

Context and motivation

Large cities in developing countries throughout the world grapple with traffic congestion. Driving restrictions are one of the most common regulations to directly lower congestion. These policies prohibit vehicles from roads on certain days, based on license plate numbers or colours. A common concern is that behavioural responses from drivers may dampen or eliminate the intended effect of the policy. Existing evidence is mixed: some studies show no aggregate effects on pollution, possibly due to some drivers buying additional and older vehicles, while several more recent studies show some reductions in pollutants and congestion (Davis 2008, Viard and Fu 2015). Little is known about the specifics of drivers’ behavioural responses to these policies, and, importantly, whether policy parameters can be tuned to improve impact.

Recently, a similar policy called “Odd-Even” has been implemented in Delhi, India, to control congestion and reduce pollution. A two week trial period was conducted in January 2016, and the policy will again be implemented for two weeks in April.

This project uses the upcoming round of restrictions in Delhi as a natural policy experiment to study the impact of driving restrictions on commuter mobility, transport choices, and traffic congestion.

Policy relevance

The Delhi government is interested in actively monitoring the impact of the Odd-Even policy. Importantly, the government has not announced its plans for future rounds of the Odd-Even policy. Thus, the evidence from this study on the impact on drivers as well as on traffic congestion, disseminated within the Transport Department of the government, will hopefully inform the government’s decision regarding the future of the Odd-Even policy.

Study design and methodology

We will measure the daily behaviour of a sample of 1200 regular drivers before, during and after the policy. During the policy, we will compare outcomes on days when a certain driver is restricted, versus days when s/he is not restricted, as defined by their car’s license plate. We will answer questions such as whether drivers are less likely to go to work on restricted days, and quantify the shifts to other transport modes.

Drivers recruited in randomly chosen petrol pumps across Delhi in early April will receive brief phone surveys throughout the study period. They will also be invited to use a smartphone app that collects rich location information based on GPS data. Half our sample was recruited during a previous study in January. Another 600 drivers will be newly recruited. The outcomes in the phone survey will include trip details on the day of the call, such as origin, destination and purpose, transportation modes, trip satisfaction and incidents. In particular, we will measure compliance with the policy. The study will cover six weeks: two before, two during, and two after the policy.

We will also collect a dataset of real-time travel time predictions from Google Maps, to explore the policy’s impact on traffic congestion.