Downtowns need two things to be successful — buildings and customers. Sounds simple.

What makes a downtown great is variety. Lots of storefronts. Restaurants, cafes, coffee shops, bars, shops, galleries, theaters. But how do you get the customers there? Well, some of them live downtown, but the rest are going to drive. And when your customers drive, they need to park. And when they park, you get restaurant, parking lot, cafe, parking lot, bar, parking lot, shop, parking lot, gallery, parking lot, theater, parking lot. And a few parking decks for good measure. Your downtown just lost its potential.

And the people that live downtown? Above the shops and restaurants? Well, we may be seeing a bit of a revival, but unless you’re offering more than bars and restaurants (think grocery store), every one of those downtown residents is going to want a car, too. And they’re going to need to park it in a convenient spot, because they’re going to drive it almost as much as everyone in the suburbs.

And now that everyone’s parked, your downtown has two tiers of street — the handful that are crammed with businesses, apartments and condos; and the surrounding areas with the parking decks, parking lots and the neglected rundown buildings between them. How do we get beyond this?

A streetcar system may be the answer. Connect your inner-ring neighborhoods, job centers and shopping districts to downtown and vice versa. It kills two birds with one stone. You get this potential market for downtown that can get there easily and leave their cars at home. And your downtown residents get connected to a wider range of services. And maybe some of them cut down on the number of cars they need because of it. Couples might need only one car between them. And, with more customers and fewer parking lots, you get the potential for more downtown businesses and more residents. The gaps fill in. It’s a virtuous circle.

I know. Streetcars aren’t cheap. But neither is suburban development. When you build your city on existing infrastructure, you’re not building new water, sewer and stormwater systems. And you don’t have to maintain what you don’t build. You have fewer miles of roads. Fewer water main breaks, snow plows, potholes and sinkholes. And come to think of it, hollowed-out downtowns aren’t cheap either. Your cities will lose their youth and ability to attract new residents without a vibrant downtown. Ultimately, it’s a choice between paying now or paying later.