When you drive alone (or take Uber alone) in a gridlocked street or freeway, you are taking more than your fair share of the limited space. When stuck in traffic, you are blocking others from moving freely.

If cities want to move people faster than walking while allowing them to take up only their fair share of space, two options arise. One is to use a vehicle that’s not much bigger than the human body, such as bicycles and scooters. Those tools work well for certain people in particular circumstances, but not for everyone. The other option is to share the ride in a vehicle. If space is really scarce, that vehicle will have to carry lots of people. In most cases, riders will have to share a vehicle with strangers, people who are not traveling for the same purposes or even to the same places. That’s what public transit is.

Fixed public transit deploys large vehicles flowing along a set path, and riders gathering at stops to use them. That way, the vehicles can follow a fairly straight line, and they don’t need to stop once for every customer. That is what makes them worth walking to get to. It is one of the best ideas in the history of transportation.

And walking is key to it. Out in low-density suburbs, residents can also drive to fixed-transit stops. But in the dense city, there’s no room for that. The microtransit promise of “service to your door” is a promise to abolish walking, and yet walking is the essence of how people share precious space.

Read: How to get more people to ride the bus

Those who prefer not to walk should be able to pilot their own tiny vehicles: a bike, a scooter, or whatever gets invented next at that scale. But the space-efficient solution, like the labor-efficient one, won’t require a driver to transport just you and a couple of others. Citizens should expect to pay full price for that.

So what technologies make sense in public transit? Efficient transit networks are made of many technologies, each the right one for its own situation. Rail is for high-capacity markets, where you need to move hundreds of people per vehicle. Ferries and aerial gondolas overcome certain obstacles. But everywhere else, the bus is the thing that’s easiest to make abundant. Because labor is the main limit on their quantity, they can be much more abundant after full automation.

If the buses are terrible in your city, you may think that buses are terrible in general. In truth, a city’s bus service is as good as its leaders and voters want it to be. Where voters have funded better bus services and cities have worked to give them priority, as in Seattle, ridership has soared.

But most U.S. cities have a large unmet demand for frequent bus service, which is why cities investing in more frequent service have seen ridership rise. Outside the largest metro areas, you can also verify this fact by comparing your city to the most similar one in Canada. There, you’ll usually find much more bus service in a city that looks a lot like yours, with rider numbers that are higher than your city’s and growing faster. Fewer people are forced to drive in those cities, too. Americans could share that benefit, and without the need for technology. Just run as much bus service as Canada does, and demand that it have the priority it needs to succeed.