The city bus ain't what it used to be.

Across the country, ridership dropped 13 percent over the last decade, according to Transportation Department data reviewed by the Wall Street Journal. Cities from Miami to Memphis to Cincinnati are reducing the number of routes and cutting the number of buses on those routes.

You might be inclined to ask, so what? There are still subways, and people have cars. But the struggles of city buses are actually a microcosm for the full sweep of America's economic dysfunction. And like many parts of the economy, it never truly recovered from the Great Recession.

When the economy nosedived in 2008, household incomes fell across the country — which also meant municipal tax revenue fell. In response, cities had to cut services like city buses. Routes became less reliable, commute times became longer, and fares became more expensive. That caused ridership to fall, which reduced the amount of money bus systems get through fares. And that forced further service cuts. "I call it the transit death spiral," Darrell Johnson, the CEO of California's Orange County Transportation Authority, told the Journal. "It's a never-ending pattern, and pretty soon you're at a bare-bones service."

This hit the poor and minorities particularly hard.

Americans who use public transit the most tend to be poorer and less white than Americans as a whole. But there's race and class segregation within public transit, too: Bus riders tend to be poorer and less white than subway riders. America's subway systems have actually boosted services and ridership by 10 and 12 percent, respectively, over the last decade.

As a result, city buses are often stigmatized as the transit system of choice for the lower classes and society's riffraff. That stigma then feeds into funding choices by local governments: Los Angeles' Bus Riders Union, for example, has been fighting the city government for decades for funneling a disproportionate share of the transportation budget into the subway system, despite buses accounting for far more of the city's overall public transit use.

So again, bus routes get cut, fares go up, stations are neglected, and buses go without upkeep (and sometimes even without air conditioning). All of which just reinforces the material divide and the cultural stigma, creating a pernicious feedback loop.

All of this, in turn, pushes low-income Americans and people of color further to the fringes of the economy. Access to reliable and affordable transportation is extremely important for Americans' ability to find work and job opportunities. For less fortunate Americans, when city bus systems struggle, that just ropes them even more tightly into poverty. The Journal spoke with two working-class Memphis residents who have to spend hours commuting on the bus each day to reach their $12 and $8-an-hour jobs. “I do it because I have to take care of my kids — I have three children and a grandson," said Priscilla Jeffries, 41. "I know it gets to me sometimes, especially when it's bad weather, raining and all of that."

"Retention is a tremendous struggle for us," added Stacy McCall, the CEO of a contract janitorial service in Memphis, and Ms. Jeffries' employer. "We have great people but their barrier to employment most of the time is their ability to get to work."

In recent decades, upper-class white Americans have also come flooding back into the cores of many American cities. That's reinvigorated property values and jumpstarted many urban economies. But it's also created a surge of gentrification that's pushed minority and low-income Americans out into outlying suburbs. And bus service to those far flung areas is more expensive, takes longer, is less frequent, and gets the budget axe sooner than service in city cores.

Throw in decades of rising inequality — which has driven wage stagnation for the poor and working class, and made it even harder for those populations to contribute to bus systems through either fares or tax revenue — and you can see how all these problems just compound and feed on one another.

So what to do about all this?

As the Journal notes, cities are experimenting with different ideas, from rejiggering transportation budgets to partnering with and subsidizing ride-sharing companies. These are often worthwhile ideas. But funding for city bus systems tends to come from a mix of rider fares, local government spending, and federal grants. And by themselves, these local efforts rely on the first two components, which both get caught up in the negative feedback loops created by recessions, inequality, gentrification, segregation, and all the rest of it.

But because it can deficit spend when the economy falters, the federal government is immune to those negative feedback loops. So if city bus systems are going to expand again, federal spending on buses will have to dramatically expand to drive that resuscitation.

There are different ways federal and local governments could partner on or divide up the administration of that spending. But the money itself will have to come from the federal level. The old system of revenue sharing, abandoned in the 1980s, could provide a model here. The federal government should dedicate permanent streams of revenue to local governments around the country to create bus systems that are robust, reliable, fast, well-maintained, and that extend well into outlying suburbs. And that spending should not waver during economic downturns. (If anything, the spending should increase during recessions, to compensate for riders' lowered ability to pay fares.)

Another thing to note is that bus systems are relatively easy to scale up. American infrastructure projects like subways and lightrails are notorious for inefficiencies, delays, and cost overruns. But for buses, you mostly need to tweak the systems already in place: buy more vehicles; hire more workers; improve routes, timetables, and maps; and dedicate more lanes.

If city buses are a microcosm for our country's struggling economy, they're also the low hanging fruit when it comes to rapidly and efficiently expanding public transit systems. A better bus system is well within reach.