Not sure what your curb has done for you lately? Not to worry. Your answer is arriving now, in the form of an equation devised by Uber that is meant to help cities evaluate how efficiently they’re using this increasingly contested space.

After years of neglect and scorn, this strip of urban infrastructure, long the sole domain of the meter maid, has gotten incredibly crowded. Bike- and scooter-share companies would love to park their wheels there. Transit agencies would love for drivers to stay out of their bus stops. Delivery drivers—the folks transporting businesses’ daily merchandise, the roughly 30 percent more UPS, FedEx, and USPS packages sent since five years ago, the 20 percent more takeout orders—would love to idle just outside their destinations. Ride-hailers like Uber and Lyft would love to pick up and drop off their passengers quickly and safely. Car owners would love to park there, ideally for free.

Yes, the curb is a contested space, which is why cities want to get better at managing it. Some are trying. Places like Washington, DC, are experimenting with reserved nighttime parking spots for Uber and Lyft pick-ups and drop-offs in one of its most hopping nightlife areas. Lyft has worked with San Francisco’s Metropolitan Transportation Agency to block its drivers from stopping on a busy street.

To do more, though, cities need data—a complete understanding of what’s happening on their roads. Plus, they need a smart way to evaluate that data, a way to come to conclusions about how curbs should be used. Oh, and also an easy way to explain those decisions to citizens once they're made.

“Converting parking to loading zones or to other uses is just a politically challenging thing to do,” says Allison Wylie, who works on transportation and mobility policy for Uber.

Which is why, in a report released last month, Uber and the transportation consultancy Fehr and Peers published what they’re calling a “curb productivity index.” It’s a way to figure out what the curb is doing for you.

The equation is deceptively simple:

Activity/(Time x Space)

“Activity” is the number of passengers using the curb space by a specific mode, “time” is the duration of their usage, and “space” is the total amount of curb footage dedicated to that use.

Here’s the example that the consultants use in their report, where a 20-foot length of curb is used for four hours as a parking spot by a single car carrying two people:

2 passengers/(4 hours x 20 feet) = .025 passengers/hour-feet, or 0.5 passengers per hour per 20 feet of curb

But if that space is instead used as part of an 80-foot bus stop serving 100 people in that four-hour block, the equation looks like this:

100 passengers/(4 hours x 80 feet) = .3125 passengers/hour-feet, or 6.25 passengers served per hour per 20 feet of curb

Clearly, the bus stop is a better use of public space.

To show how this equation might work in the real world, the researchers collected 12 hours worth of video footage, photographs, and Uber data for five locations in San Francisco. They concluded that, yes, it sometimes makes sense to convert parking spots to other uses, like Uber pick-ups and designated loading zones. It also makes sense to make curbs flexible—to use them for parking at some times of day and other functions at others.

“This is an easy-to-use, easy-to-understand way to communicate the benefits of turning over parking in very busy downtown centers to more productive uses,” says Wylie. She notes that cities that can’t collect their own precise data should also be able to use the five examples in the report, each a different sort of street, to reach their own curb conclusions.