How To Make Nightmare Traffic: Eliminate HOV Lanes

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A new study from Harvard and MIT researchers — published in the journal Science — suggests that the most effective way to grind traffic to a halt in a major city is to eliminate high occupancy vehicle policies. The results were observed in the pure havoc that ensued when Jakarta, Indonesia eliminated its quarter-century old high occupancy vehicle lanes in 2016.

Jakarta had introduced its “three-in-one” HOV policy in 1992, where vehicles in the high occupancy lane were required to have three people inside, in the heavy traffic hours between 7:00 a.m. and 10:00 a.m., and in the afternoon between 4:30 p.m. and 7:00 p.m.  Jakarta’s population of 30 million people makes commuting a nightmare in the best of circumstances.

The HOV policy was anecdotally successful, but it also had its critics, mostly due to the presence of “jockeys” who would charge drivers a fee to ride along, thereby increasing the number of passengers in the car to the three-person minimum. Commuters would pick up jockeys just before the start of the HOV lanes and drive them into the city. It’s something that occurs in cities like San Francisco, too.

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Suddenly, in March of 2016, Jakarta’s administrators dumped the program, first for a week, then for a month, and finally permanently. For commuters it was a nightmare, but for Ben Olken, a professor of economics at MIT, Gabriel Kreindler, a doctoral candidate in development economics in the MIT Department of Economics, and Rema Hanna, the Jeffrey Cheah Professor of South-East Asia Studies at the Harvard Kennedy School, it was a windfall. It allowed them to study traffic patterns and learn the results of a decision to eliminate HOV lanes.

The researchers queried Google Maps data in late March, before the policy was eliminated, and they continued monitoring into June of 2016. “The key thing we did is to start collecting traffic data immediately,” Hanna explains. “Within 48 hours of the policy announcement, we were regularly having our computers check Google Maps every 10 minutes to check current traffic speeds on several roads in Jakarta. … By starting so quickly we were able to capture real-time traffic conditions while the HOV policy was still in effect. We then compared the changes in traffic before and after the policy change.”

The results were dismal. Every measurable data point related to traffic got worse. The average average speed of rush hour traffic dropped from 17 to 12 miles per hour in the mornings, and even more dramatically, cut more than half from 13 to 7 miles per hour in the evenings. 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. Most people walk at 3 miles per hour; a reasonably fit jogger can keep up a 7 mile per hour pace with ease.

“Eliminating high-occupancy vehicle restrictions led to substantially worse traffic,” says Olken. “That’s not shocking, but the magnitudes are just enormous.”

The 87 percent increase in evening commute time had a drastic impact, not only on the highways, but on surrounding streets, as well. As drivers tried to find ways around the highway blockages, traffic increased on secondary roads, magnifying the problem. Instead of funneling traffic onto the central roads, the policy change made congestion worse all over.

“HOV policies on central roads were making traffic everywhere better, both during the middle of the day and on these other roads during rush hour,” Olken observes. “That I think is a really striking result.”

The paper, “Citywide effects of high-occupancy vehicle restrictions: Evidence from ‘three-in-one’ in Jakarta,” is being published today in the journal Science.


Craig Fitzgerald

Craig Fitzgerald

Writer, editor, lousy guitar player, dad. Content Marketing and Publication Manager at