If the enthusiasts are to be believed, driverless, electric cars will augur the end of all of humanity’s traffic woes. With nifty “mobility-on-demand” at our fingertips, we will live in cities that — as one autonomous driving start-up imagines — have “no congestion, zero traffic fatalities, instant parking available on demand, safe routes for cars, bikes and pedestrians and modern, efficient, up-to-date infrastructure.”