Over the four years of the study, the number of cars in Manhattan seeking ride-hailing fares increased by 81%. There are now about 68,000 ride-sharing drivers across New York city. That's about five times the number of distinctive yellow cabs licensed to operate there, he found. There are so many, his work suggests, that they spend about 45% of their time empty just cruising for fares. That is a lot of unused cars clogging a lot of busy streets.