What price parking?

A fledgling service that would let people find and reserve parking spaces via their cellphones could make life easier for those who use it. Less clear is whether the system, to be launched by the Cambridge firm SpotScout.com, will help the city as a whole. For there is more to parking than merely parking.

The demands of the automobile exert considerable force on American urban life -- even in central Boston, which was designed for pedestrians and horse-drawn carriages. For reasons ranging from the weather to force of habit to the unpredictability of the T, people who plan to eat out or shop in town often opt to drive instead. The well-being of some businesses, not to mention the sanity of some residents, hinges on how many motorists can park and how long they stay when they do.

A fair sharing of scarce parking space is vital. The Boston Transportation Department is understandably wary of SpotScout's plans, especially if they involve on-street spaces.

What company founder Andrew Rollert envisions is a clearinghouse for parking spaces of all sorts. Owners of spaces would post vacancies on SpotScout. Motorists looking for spaces would enter a location into their cellphones, and the company would generate a list of possibilities. This would work well with pay garages and, in theory, with spaces in private driveways. (Whether renting out driveways is legal in Boston is another question entirely.)

But Rollert also hopes to guide customers to metered parking spaces on public streets. A driver who expects to leave such a space -- and earn some extra change -- would post a departure time, and SpotScout users would pay to find out where to go.

Rollert insists this doesn't amount to saving spaces, because the person who's planning to vacate a spot wouldn't know who bought the information. Still, if the system worked as intended, SpotScout users would have an inside track on publicly-owned parking spaces. At worst, SpotScout could turn into the on-street-parking version of a leaf blower -- an "advance" that helps its users but annoys everyone else.

In an interview, Boston Transportation Commissioner Thomas Tinlin praised Rollert for thinking innovatively, and stressed that the city won't decide anything before hearing him out. But Tinlin also worries about upsetting a balance. Will motorists who buy inside information park for longer than those who merely happen by their spaces?

Vacant spaces rarely stay open long, and filling them up even faster has a clear downside. Already, commerce in some neighborhoods depends on the delusion that, if one circles the block enough times, an on-street space will come open. If wishful thinking gives way to certainty that there's nowhere to park, motorists who'd otherwise visit a given neighborhood might stay away altogether.