This is a headache for the operators of public-transport systems.
It is also a problem for cities.
Like it or not—and many people do not—mass public transport does some things very well.
It provides a service for people who are too old, too young, too poor, too fearful or too drunk to drive or ride a bike.
Trains and subways cause less pollution than cars and move people at far higher densities.
The danger is that public transport could become a rump service,
ever less popular and ever less good, partly because of its unpopularity.
Fewer passengers mean fewer trains and buses,
which leads to longer waits for those who persist with them.
Cars, whether driven or driverless, will clog the roads.
To some extent, that dystopian future can be seen off by pricing road use properly.
Many cities, particularly in America, generously subsidise driving by forcing developers to provide lots of parking spaces.
Elsewhere, cities have created congestion-charging zones.
But that is a hopelessly crude tool.
Most congestion zones in effect sell daily tickets to drive around as much as you like within the zone,
and charge nothing to vehicles such as taxis and minicabs.
It would be much better to charge for each use of a road, with higher prices for busy ones.
Transport agencies should also embrace the upstarts, and copy them.
Cities tend either to ignore app-based services or to try to push them off the streets.
That is understandable, given the rules-are-for-losers attitude of firms like Uber.
But it is an error.
Although new forms of transport often compete with old ones in city centres,
they ought to complement each other in suburbs.
Taxi services and e-bikes could get people to and from railway stations and bus stops,
which are often inconveniently far apart outside the urban core.
It is doubtful that most people make hard distinctions between public and private transport.
They just want to get somewhere, and there is a cost in time, money and comfort.
An ideal system would let them move across a city for a single payment,
transferring from trains to taxis to bicycles as needed.
Building a platform to allow that is hard, and requires much sweet-talking of legacy networks as well as technology firms—though a few cities, like Helsinki and Birmingham, in England, are trying.
It is probably the secret to keeping cities moving.