If there is still one car for one person making each leg of the trip, the on road utilization has not changed. The parking utilization has been reduced, however, which then could open more lanes and increase density.
The road utilization has increased as well as the fuel usage for the driving between passenger drop offs and pickups. As well as the commute of the Lyft driver. That said, if it causes people to take the train the next 25 miles into the city as opposed to driving it could actually decrease.