Heavy traffic in Jakarta after carpool lane policy lifting.

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Getting rid of carpool lanes could double travel times

If you live in a highly congested city and spend hours in traffic, you may think your commuting couldn’t get any worse. Think again. Eliminating carpool lanes could almost double drivers’ traveling times, according to a new study.

“I was surprised by the magnitude of these effects,” says Antonio Bento, an expert in environmental economy at the University of Southern California in Los Angeles.

The findings come thanks to an unusual decision made by the government of Jakarta last year. Following allegations that drugged babies from poor households were being used as “jockeys,” or passengers for hire, Indonesian lawmakers repealed the so-called three-in-one restriction. The law had required cars driving on the business district’s main roads to carry at least three passengers during rush hours.

To determine the impact on the city’s drivers, Benjamin Olken, an economist at the Massachusetts Institute of Technology in Cambridge, and colleagues queried Google Maps for real-time driving-speed data before and after the new policy went into effect. Following the policy lift, travel delays, defined as the time it takes to travel 1 kilometer, increased by 46% in the morning and almost 90% in the evening, the team reports today in Science.

Minutes/kilometer Time 4:30 – 7 p.m. 6 a.m. –7 a.m. 7 p.m. – 8 p.m. 7 a.m. – 10 a.m. 8 p.m. – 6 a.m. 10 a.m. – 4:30 p.m. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 With restriction law After restriction law lifted Road that had restriction With restriction law After restriction law lifted Alternate road, never had restriction Effects of lifting Jakarta's“three-in-one” policyAfter the policy was repealed, average traveling times increased at times of the day and on roads where there had never been restrictions in place. Rush hours
V. ALTOUNIAN/SCIENCE

But the most startling result is that phasing out the three-in-one policy led to worse traffic during times of the day and on roads where there had never been restrictions in place, Olken says. One possible explanation, he says, is that the three-in-one restriction led fewer people to drive into the city. “Maybe they carpooled, took public transit, or worked from home.”

The new study is significant because it suggests that carpool lanes are key tools to deal with congested urban areas, especially in countries where economic inequalities make other types of policies—such as congestion taxes—unpopular, says Michael Anderson, an economist at the University of California, Berkeley. “The fact that the effects are so large suggests that developing countries should think about it very seriously.”