With these documented failures in mind, I worked with colleagues to study policies that might be more effective. With MIT’s Benjamin Olken and Kreindler, we examined the impact in Jakarta, Indonesia, of the widespread policy of high-occupancy vehicle (HOV) restrictions, which limit travel based on the number of passengers in a car.
Jakarta has some of the worst traffic gridlock in the world. Since the early 1990s, Jakarta’s government has sought to improve traffic flows with a rule that private cars driven during rush hours in the city’s central business district must contain three or more passengers. Just about everyone despised this “three-in-one” policy, and people often complained that it created further inconvenience, without reducing time spent on the road. Our research sought to quantify the policy’s true impact.
In defending the view that the policy was onerous and ineffective, drivers often pointed to an informal business of enlisting “professional” passengers. These “jockeys” would wait near the entry points of Jakarta’s three-in-one roads, and, for about 15,000 rupiah ($1.10), accompany drivers so their vehicle would be in compliance. Lone drivers in need of two additional passengers could hire a mother and baby. According to the policy’s opponents, what looked like carpooling was an evasion of it.
Eventually, the Jakarta government sided with the policy’s naysayers, announcing in March 2016 that the rules would be suspended indefinitely.
For researchers, this created a golden opportunity to measure the impact of a policy before its adoption and immediately after its repeal. To do that, we queried a Google Maps interface every ten minutes, 24 hours a day. With this real-time, crowd-sourced traffic data for each route previously under restriction, we were able to ascertain what happened to traffic flows after the policy was suspended.
The results were striking. Despite what drivers – and eventually the government – believed, the three-in-one policy was highly effective in reducing congestion. Our data showed that traffic congestion worsened significantly after the policy was rescinded. On Jakarta’s regulated roads, average speeds fell from 28 kilometers (17.4 miles) per hour to 19 kilometers per hour during the morning rush, and from 21 kilometers per hour to 11 kilometers per hour during the evening rush.
Moreover, we found increases in traffic at times of day that were not previously regulated, and more vehicles appearing on non-regulated roads in general. Thus, suspending the three-in-one policy produced more traffic and less carpooling.
These findings have implications for traffic-control measures in other cities. For example, our data imply that Jakarta’s HOV restrictions were more effective than London’s congestion pricing or Delhi’s even-odd policy. The findings also suggest that while Jakarta’s “jockeys” were a visible presence, they did not weaken the effect of the policy.
As megacities continue to emerge in many developing countries, strategies like Jakarta’s three-in-one approach can help reduce gridlock. But they can succeed in delivering benefits only if they are crafted wisely, enforced effectively, and studied well. People will always seek to circumvent regulations, but policymakers must consider all the evidence before they decide to take the off-ramp.
This article first appeared in Project Syndicate.