An abrupt halt to a policy aimed at reducing traffic delays in Jakarta has provided researchers with valuable insights into how carpooling affects traffic flow within the megacity. Ending the policy - which required each car to hold a minimum of three passengers on designated major streets during rush hour - resulted in a 46% increase in travel time during morning rush hour and an 87% increase during evening rush hour. Worldwide, cities are struggling to support the transportation needs of residents. In U.S. metropolitan areas such as New York, people spend on average more than an hour a day commuting to and from work. In São Paolo and Rio de Janeiro travel times are even higher, at 1.5 hours per day, on average. In attempting to reduce these travel times, some cities implement policies that create "high-occupancy vehicle" (HOV) lanes, even while the benefits of these policies have sometimes been unclear. Traveling in them requires a minimum number of people to ride in a car, particularly during peak traffic times. Perhaps the most extreme example of HOV restrictions anywhere in the world to date has been the "three-in-one" policy implemented in Jakarta, Indonesia, a city supporting a population of more than 30 million. In March 2016, however, the city announced plans to cancel the HOV policy within seven days. Within 48 hours of this announcement, Rema Hanna et al. began querying Google Maps to collect data on traffic on major HOV roads, as well as two alternate roads that ran parallel to the HOV roads; they continued to collect and analyze traffic data as the HOV policy was lifted several days later. Remarkably, 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. Increases in travel time were also observed outside of rush hour. These findings suggest that the HOV policy, which some had suspected to be ineffective, likely helped reduce the overall number of cars on the road in this congested city, the authors say.