Traffic policies for megacities

CAMBRIDGE — Urbanization has many advantages. By bringing people together physically, cities inspire innovation, fuel opportunity, bring workers closer to jobs, and facilitate the diffusion of arts and culture. But the benefits are often accompanied by costs.

Perhaps none feels more burdensome—and infuriating—than traffic congestion. Packed roads and bumper-to-bumper traffic mean time wasted and workdays shortened. And stationary vehicles still emit exhaust fumes, damaging the environment and human health.

Many governments have tried to develop policies to cut traffic congestion by making it more expensive to drive. Since 2003, London has successfully implemented a congestion charge, while Singapore wants to use GPS technology to police its own congestion-pricing strategy.

But such policies are harder to implement in poorer countries that lack technological capabilities and infrastructure. That is why developing countries typically seek more basic policies to improve traffic flows.

In India, Delhi’s suffocating air pollution has led the government to experiment with “even-odd” policies: People can drive only on certain days, based on the numbers on their license plates. But this approach has had minimal impact. Gabriel Kreindler of the Massachusetts Institute of Technology has shown that while the policy reduced congestion slightly, drivers circumvented it by switching to other vehicles. Vendors also sold old plates so that drivers could change theirs as needed.

Sadly, India did not learn from other countries’ experience. Research by Lucas Davis of the University of California, Berkeley, had already shown that a similar policy, implemented in Mexico City in 1989, did not reduce air pollution—the intended goal—or significantly ease traffic congestion. As in Delhi, drivers in Mexico City found many ways to skirt the rules.

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 high-occupancy vehicle (HOV) restrictions, which limit travel based on the number of passengers in a car.

Jakarta has some of the world’s worst traffic gridlock. Since the early 1990s, Jakarta has sought to improve traffic flows with a rule that private cars driven during rush hours in the city’s central business district must carry three or more passengers. But the people complained that this “three-in-one” policy, led to further inconvenience without reducing time spent on the road. Our research sought to quantify the policy’s true impact.

In saying that the policy was onerous and ineffective, drivers often cited 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. What looked like carpooling amounted to an evasion of it.

In March 2016, the Jakarta government announced the indefinite suspension of the policy.

For researchers, it was a golden opportunity to measure a policy’s impact before its adoption and immediately after its repeal. To do that, we queried a Google Maps interface every 10 minutes, 24/7. 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 HOV policy was highly effective in reducing congestion. Our data showed that congestion worsened significantly after the policy was rescinded. On Jakarta’s regulated roads, average speeds fell from 28 kilometers per hour to 19 kph during the morning rush, and from 21 kph to 11 kph during the evening rush.

We also found increases in traffic at times of day that were not previously regulated, and more vehicles appearing on nonregulated roads in general. Thus, suspending the HOV 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 policy’s effect. Project Syndicate

* * *

Rema Hanna is codirector of the Evidence for Policy Design research program at Harvard University.