Life in many major U.S. cities has settled into a new, stuck-at-home routine. Activity in public, measured by demand for public transit, has leveled off at about 30 percent of where it used to be. It could stay this way for months.

In this data-starved environment, public-transit demand is a relatively well-focused lens with which to view the pandemic’s economic effect. The coronavirus recession was caused, at its heart, by one thing: the end of in-person economic activity, particularly in locked-down densely populated areas. The economy is in free-fall, because people can’t go anywhere, from work or school to brewpubs and ballgames. That’s what transit measures.

Mass transit is centered in the cities hit hardest in the pandemic’s early phase, and it serves many of the low-income service workers who, early on, bore the brunt of the epidemic. Just as important, transit data is extremely responsive to government restrictions, which vaporized economic activity in the name of saving hundreds of thousands of lives.

From March 9 to March 23, activity on U.S. transit systems went from normal to just 31 percent of the usual level, according to the Transit app, which millions use to check for the next train or plan their bus transfers. In the week-plus since March 23, it has stuck at about 30 percent.

We’re looking at cities with the most public-transit commuters in the chart below, and New York City looms large in the nation’s transit statistics, but the app’s coverage is broad. Every time users open Transit, they contribute anonymous real-time data for everything from the Kansas City Area Transportation Authority (down 45 percent as of Tuesday) to Bay Area Rapid Transit (down 84 percent on the same day). Here are rates for the cities with the most public-transit users.

The public routines that governed our lives have literally flattened out. Rush hour has withered to a bump with about as much demand as there used to be at midnight. People still use mass transit, particularly that smaller group of new front-line heroes — workers bringing folks food from restaurants and online shops, and those working in grocery stores and pharmacies.

To be sure, not everybody takes transit. In many smaller cities and rural areas, options are limited. But for the moment, and this phase of the pandemic, it’s one of the earliest national measures we have for the type of activity that’s been disrupted by the crisis.

Based on what we’re seeing, it almost looks like American cities have survived the initial wave of shelter-in-place orders and are hunkered down for the long haul.

Have we hit bottom?

In every downturn, there comes a turning point where the downward-sloping lines on the charts pull out of their tailspin and begin the long climb back to normal. The transit charts are flattening. Activity in cities has leveled off. Does that mean we’ve bottomed out? Is this as bad as it’s going to get?

No.

The economy has further to fall. We’ve already slashed physical activity — and may not be able to cut it much further without losing access to necessities — but the fallout will continue to ripple through less-visible corners of the economy.

Bills will be due in the next few days — weeks before the first stimulus checks are expected to arrive — and many won’t have enough to cover it. Before the downturn, in 2018, a Federal Reserve survey showed about 17 percent of U.S. adults said they expected to skip at least one bill during the month they were surveyed. Many groups are under even more pressure — the comparable number for black Americans with a high school education or less was 34 percent.

How would they fare if they missed a paycheck? We can guess: That same survey asks how those numbers would change if they had to cover a $400 emergency expense. Coincidentally, $400 is just a bit more than the average restaurant or bar worker earned in February, Labor Department data shows.

If they were hit with a $400 emergency, 29 percent of Americans would have to skip a bill. For the hardest-hit group, which again is black Americans with a high school education or less, that jumps to 58 percent. And that’s after missing just one week’s pay. Data from Transit shows the national slowdown has been going on for several weeks, and most restrictions on activity are expected to continue at least through the beginning of May.

As workers struggle, their pain will radiate outward to the businesses that depend on them and the cycle will continue.

What number will mark the real bottom?

Trains and buses are the first public spaces many lower-income Americans will encounter once their city or state’s lockdown ends and will be an early signal of the coming thaw.

In China, subway traffic is picking up, albeit with temperature checks at the entrances. And when people are comfortable riding public transit in large numbers once more, we’ll know the old normal is back.

Transit ridership isn’t the first number we should watch. Experts say transit data depends on another variable: stay-at-home orders and restrictions on public activity. Those restrictions ultimately depend on one thing: coronavirus infection totals.

Since the earliest days of the outbreak, economists have cited stopping the spread of the virus as the top economic priority. Until we’ve addressed the public-health catastrophe, and people are willing to ride the 7 train or take the bus to the 7-Eleven without fear of spreading a deadly virus, nothing will recover. If you want to know when things are going to turn around, wait for new cases to subside.