Higher Occupancy, Lower Traffic: The Effectiveness of HOV Lanes

July 6, 2017
By Doug Gavel

Drivers in major cities around the world spend hundreds, if not thousands, of hours stuck in traffic each year. Transportation planners have tried multiple interventions, including the imposition of high occupancy vehicle (HOV) restrictions during certain hours on certain roadways. The effectiveness of these restrictions work has been a matter of some debate, but new research published in Science documents how HOV policies in Jakarta, Indonesia, have significantly reduced travel delays by improving traffic conditions in and around the city.

The research report is co-authored by Rema Hanna, Jeffrey Cheah Professor of South-East Asia Studies at Harvard Kennedy School (HKS), whose work in the field of environmental policy and the provision of public goods in developing countries has garnered important insights for the development of effective public policy. 

In Jakarta, Hanna and her fellow researchers examined traffic speed data from Android phones collected through Google Maps to determine the impact of the city’s decision in April 2016 to suddenly lift HOV restrictions on certain high-traveled roadways. Until that time, the city’s “three-in-one” policy, first introduced in 1992, required all private cars on two major roads to carry at least three passengers during peak hours.  

“This is an ideal setting to study traffic congestion policies. With a population of more than 30 million, Jakarta is the world’s second-largest metropolitan area, second only to Tokyo,” the authors write. “Virtually all commuters in the region use the roads in some form or another; the city has no subway or light-rail system and only a limited commuter rail network. Not surprisingly, it has some of the world’s worst traffic.”

The research team examined the impact of the policy change on both the two roads which had the three-in-one restrictions, as well as other nearby roads where traffic would be expected to divert. Their findings were unambiguous.

”After the policy was abruptly abandoned in April 2016, delays rose from 2.1 to 3.1 minutes per kilometer (min/km) in the morning peak and from 2.8 to 5.3 min/km in the evening peak. The lifting of the policy led to worse traffic throughout the city, even on roads that had never been restricted or at times when restrictions had never been in place…. The results therefore suggest that quantity restrictions on severely congested roads can have beneficial spillover effects on traffic throughout the city, whether by potentially eliminating hypercongestion or by getting cars off the road.”

The full article in Science is available online. A longer version of the article is posted on Hanna’s Harvard Scholar site.


Research from Rema Hanna shows the effect HOV policies have on travel delays in Jakarta, Indonesia.


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