‘Ridehailing’ services such as Uber are making traffic congestion worse rather than more efficient according to a newly-published study. The results contradict previous studies and forecasts.

Bruce Schaller explored data from New York streets over the past four years. He notes that the number of licensed ‘ride-sharing’ drivers is around five times the number of licensed traditional yellow cabs. That’s led to an oversupply of empty cars on the roads waiting for a fare, making traffic worse.

Part of the logic of ridesharing apps being more efficient is that it makes it more viable to do without a car. In Manhattan at least, however, it appears people are instead switching to Uber and the like from public transport, meaning more vehicles on the roads rather than fewer. It also appears that the convenience of the apps means people may be taking some journeys that they’d otherwise not have made at all.

Another problem identified in Schaller’s report is that the idea that surge or other variable pricing helps spread out demand doesn’t really play out in Manhattan. The number of trips more than doubles between 4pm and 6pm but the supply of drivers increases to meet it, so there’s no incentive for passengers to wait until later.

Schaller says the biggest single factor to tackle in both traditional taxis and app-based services is to reduce the average time cars are empty while waiting for a new fare. That could be tricky both from a technical perspective and in how much taxi and app providers can be forced or incentivized to change how they operate.