Driverless shuttles are on the road in Reston, Va., a suburb of Washington, D.C., and while things are going pretty well so far, the pilot has also highlighted why driverless cars may still be some time away.

The shuttles take people to and from remote parking in an area largely under construction. Some project participants say that while they’re working fine with a rescue driver and engineer on board just in case, it’s also become clear that what works in a lab may not be ideal for on-street operation. The vehicles can’t tell if someone opens a door while in motion, for example, and they don’t know what to do about parents loading strollers. They’re also restricted to speeds of less than 25 miles per hour and while that may prevent pedestrian fatalities, it’s awfully slow for getting around.

The Washington Post offers an analysis of the project; read it here.