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

• Driving restrictions based on license plate numbers are a popular yet little understood policy in large cities in developing countries.
• This project used high frequency surveys to measure how drivers responded to such a policy in Delhi.
• Delhi's Odd-Even policy proved effective in reducing traffic congestion. However, many drivers switched to other private vehicles, while some cancelled travel plans.

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. Little is known about the specifics of drivers’ behavioural responses to these policies, and, importantly, whether policy parameters can be tuned to improve impact.

A policy called “Odd-Even” has recently been implemented in Delhi, India, to control congestion and reduce pollution. This project studied the impact of driving restrictions on commuter mobility, transport choices, and traffic congestion.

We measured the daily behaviour of a sample of 1200 regular drivers before, during and after the policy. During the policy, we compared outcomes on days when a certain driver is restricted, versus days when they are not restricted, as defined by their car’s license plate.

Consistent with critics of driving restriction policies, we found that in the short run around half of affected drivers were able to lawfully bypass the restriction by switching to existing unrestricted private travel vehicles. Moreover, some drivers cancelled trips, including work and business related trips, pointing to a real economic cost. However, the policy also led to a precisely estimated decrease in average driving travel time. There is suggestive evidence that these effects will be broadly similar during an anticipated second round of the policy.

The evidence points to driving restrictions being a successful policy to contain traffic congestion as an emergency measure and/or in the short-term.