New Haven has a parking problem. But it is not just because there are too few spaces, Donald Shoup ’62 GRD ’68 told a packed audience at Sudler Hall Tuesday evening.

In the core of Yale’s campus, the parking shortage has grown as the University builds new buildings on land that used to be surface parking lots, according to University Director of Sustainable Transportation Systems Holly Parker, who helped organize the discussion of “Traffic, Parking, and our Green Future.” At the event, Shoup and New York Times bestselling author Tom Vanderbilt addressed urban parking and its environmental costs.

[ydn-legacy-photo-inline id=”8740″ ]

“Parking is free to us only in our role as motorists,” Shoup said. “Just because we don’t pay for parking doesn’t mean that the costs cease to exist.”

Shoup, a world-renowned transportation and land-use expert, kicked off the discussion by saying cities need to reduce the number of drivers trolling the streets for parking because doing so causes congestion. He explained that cities should price street parking so that 15 percent of spaces are always available, a practice that would limit car cruising.

In addition to cruising, idling is another environmentally hazardous traffic problem, Vanderbilt said, citing the fact that, by idling, Americans consume the same amount of energy that Costa Rica does in a year.

Even though New Haven’s traffic and parking policies are in the city’s domain, Shoup said there are steps Yale can take to improve the efficiency and sustainability of its transit systems.

Shoup said Yale could collaborate with public transportation companies, like the public bus company CTTransit, to offer more varied and cheaper travel options to the Yale community.

“Many universities do this now — It’s called a Upass or Unlimited Access,” Shoup said. “Once the university starts it, everyone else seems to love it, and it draws some people out of their cars, so I think it would help Yale’s parking shortage.”

Yale’s shuttle system and parking costs more than $3 million a year, Shoup said, all of which Yale pays. A system such as Upass would be much cheaper for the University, he said, because the state and federal governments would subsidize the systems. Parking is a great cost to the University and not nearly covered by the amount individuals pay to use garages, Parker said. The new School of Management campus, for example, will have about 200 parking spaces, Parker said. But each of those spaces, if underground, will cost the University more than $100,000 just to build — much less to operate and maintain.

The end of the event left the roughly 100 attendees with many questions about how Yale and New Haven should cope with parking shortages.

“I guess I’d never thought about the market forces of parking, and how, just like with any other market force, you can use incentives, and disincentives to discourage people from driving into the downtown core,” New Haven resident Jonathan Richardson FES ’11 said. “The question I’m really leaving with is that issue of safety. … If you really increase the price and make parking less attractive so that more people decide to walk, does that make people more vulnerable?”

Richardson added that he and his wife usually walk everywhere — as long as it is before 8 p.m. — and that when they do drive downtown, they often struggle to find convenient parking.

Mark Aronson, chief conservator of paintings at the Yale Center for British Art, said he usually bikes the 1.5 miles to work from his East Rock home. But Aronson said this approach is the exception, not the norm.

“Absolutely I agree that we have too much parking, and I go to a lot of meetings at the museums at Yale where people discuss the need of proximate parking for people to come to our museums,” he said. “I always say that New Haven doesn’t have a parking problem — New Haven has a walking problem.

Curb parking in downtown New Haven costs $1.25 an hour.