Changes in carpooling restrictions in Jakarta are linked to an increase in travel times during the city's rush hours. | Rema Hanna and Benjamin A. Olken
An abrupt end to a carpooling policy in Jakarta, Indonesia, led to a 46% increase in travel time during morning rush hour and an 87% increase during evening rush hour, according to a study published in the July 7 issue of Science.
Worldwide, cities are struggling to support the transportation needs of residents. In U.S. metropolitan areas such as New York and Washington, D.C., people spend on average more than an hour a day commuting to and from work. In São Paolo and Rio de Janeiro in Brazil, travel times are even higher, at 1.5 hours per day on average.
In attempting to reduce travel times, some cities implement policies that create "high-occupancy vehicle" (HOV) lanes. Traveling in them requires a minimum number of people to ride in a car, particularly during peak traffic times. Among the strictest HOV restrictions adopted across the globe has been the "three-in-one" policy that also was implemented in Jakarta, Indonesia, a city with a population of more than 30 million. The policy required each car to hold a minimum of three passengers on designated major streets during rush hour.
HOV policies can be controversial. Rema Hanna of Harvard University, an author of the study who has firsthand experience with traffic in Jakarta said, "The key issue with HOV policies is that they remove existing lanes from use by general traffic … the question is about whether the additional carpooling behavior makes up for the loss in road space."
In the case of Jakarta, an additional factor is at play, Hanna explained. "In Indonesia there were professional passengers, called jockeys, who stood right outside the entrance to the HOV areas. So if you were short a passenger you could hire a jockey to be the third passenger, for a little over a dollar. Some people thought that the fact that these jockeys existed made the whole policy moot."
Amid the controversy and uncertainty surrounding Jakarta's HOV policy, in March 2016 the city announced plans to cancel the policy within seven days.
"For us, this was the perfect opportunity to study questions around HOVs and so we sprang into action to start collecting data to do so," said Hanna. "Within 48 hours of the policy announcement we were querying data from Google Maps every 10 minutes to check traffic conditions in Jakarta. We included both the main roads affected by the policy change, as well as other roads in the network in order to understand how traffic was changing citywide."
Lifting the HOV policy had a profound effect across the city. "After the restriction was lifted the evening traffic was moving at only 11 kilometers an hour — about 7 miles an hour — which is really not much faster than walking," said Hanna.
Lifting the HOV policy not only caused dramatic increases in travel time along the previously designated HOV roads, but along the parallel roads as well. The researchers also observed increases in travel time outside of rush hour. These findings suggest that the HOV policy, which some had suspected to be ineffective, helped reduce the overall number of cars on the road in the congested city.
"In the future, we would like to use finer data to gain a better understanding of how commuters value alternatives to using their cars during the peak-time, such as using public transport or carpooling," said Hanna. "Another line of future research is to use Google Maps road speed data in the context of other natural experiments in Jakarta and other cities around the world, to understand the traffic impact of traffic policies such as driving restrictions, road pricing and introduction of new subway lines."