Our research was technically right, but we had not taken into account changes in human behavior. Cars are more convenient and comfortable than walking, buses and subways — and that is why they are so popular. Make them even cheaper through ride-sharing and people are coaxed away from those other forms of transit.
This dynamic became clear in the data a few years later: On average, ride-hailing trips generated far more traffic and 69% more carbon dioxide than the trips they displaced.
We were proud of our contribution to ride-sharing but dismayed to see the results of a 2018 study that found that Uber Pool was so cheap it increased overall city travel: For every mile of personal driving it removed, it added 2.6 miles of people who otherwise would have taken another mode of transportation.
Regardless of anything else, there are no circumstances under which companies like Uber would decrease traffic. This is because of two effects: Firstly, any regular car ride replaced with an Uber ride will result in more road-hours, since there is now a car travelling to your pickup point as well travelling on the road after dropping you off.
Secondly, the convenience of Uber can cause more travellers taking a car instead of public transport, again increasing the total number of road-hours.
Is there even a hypothetical scenario under which any of these private hire companies would reduce traffic? The only theoretical benefit is that less parking spaces are needed.
