The gray buses that roll along Los Angeles' Orange Line don't look like other buses: They're 60 feet long, and their streamlined design means they don't just stop. With some pomp, they arrive. They dock. And today, on a drizzly Sunday, nearly every seat on the Orange Line is taken. The route connects the northwest corner of the San Fernando Valley to a Metro Rail station in North Hollywood, 18 miles and about an hour away. It's perhaps the country's best example of “bus rapid transit,” a grade of service that's supposed to combine the best features of a trolley line with the relative cheapness of a bus. People dig it. Today, the woman next to me is speaking quietly into her phone in Russian; next to her a guy is watching Instagram videos about elaborate bong hits. Two riders are talking about using analytics to provide better customer service, sitting across from a man in a red knit cap carrying his belongings in a black trash bag. Kids in Dr. Martens and torn black T-shirts jostle with people in boots muddied from work.

Part of what makes the Orange Line so fast and so popular is that it's protected from street traffic in a dedicated, manicured lane of its own. That lane cuts a demographic and geographical transect through typical Southern Californian sprawl. The sides of the busway are landscaped and a bike path runs parallel, but at crossings, when you can see up and down intersecting streets, the view is of strip malls, liquor stores, car dealerships, and boxy apartment buildings butting up against single-family homes. It's a road to Hollywood paved with irony: LA once had the most extensive rail transit system in America but tore it up for cars in the middle of the 20th century. This right-of-way used to be one of the rail lines.

The Orange Line carries more than 20,000 people every weekday. But setting this route aside, bus ridership has gone off a cliff, here and nationwide. Some 2,300 buses run around LA every day—165 routes covering almost 1,500 square miles, for a total of 73 million miles a year. Ridership is down 36 percent this decade, and most cities in the US have seen similar declines. Last year, the number of people using transit fell in most of the biggest metro systems—and that was an improvement over the year before.

No one's really sure why. Some researchers think people with enough money may have switched to services like Uber and Lyft, though it's likely those trips replaced private car travel, not transit. Another hypothesis is that after the 2008 recession, cars and car loans became very cheap. LA may not be as decentralized as cliché would have it, but it is multicentric and, well, eccentric when it comes to the places people live, work, and shop. The right-wing think tank Cato Institute says public transit makes sense only when one central area in a city has most of the jobs, and anywhere else it's too slow and too expensive. So why even bother? Cars are too damn great.

That certainly feels true when you look down on Los Angeles—a meshwork of highway laid over a fractally complex mesoscale of avenues and boulevards and a microscale filigree of surface streets. Ubiquitous freeways, scenic coastal highways, long straightaways reaching from the mountains to the beach—it's a town made for driving.