The cost of cutting public transit service by 35 percent could far exceed the $47 million that is needed to avoid the cuts, according to various projections.

If the Port Authority loses 15 percent to 22 percent of its ridership after the proposed Jan. 9 cuts, as it predicts, those displaced riders would spend an additional $135 million to $198 million annually to drive and park, based on American Public Transportation Association calculations.

The association releases an annual study of the savings enjoyed by transit riders. This year's report, issued in April, concluded that riders in Pittsburgh save $8,174 each year on gasoline, parking, maintenance and other automotive costs.

Based on authority ridership figures, the cuts would cause a drop of 33,000 to 48,000 passenger trips on a typical weekday, or the equivalent of 16,500 to 24,000 round-trip riders.

Chris Sandvig, project manager of the Pittsburgh Community Reinvestment Group's GoBurgh Initiative, which has studied the benefits of transit in stimulating development, said Wednesday the actual costs would be far greater than those absorbed by displaced riders.

He estimated that $100 million to $200 million in infrastructure spending would be required to accommodate the additional traffic generated.

With Downtown parking already scarce and the city proposing to lease its parking garages to a private operator, increased demand could cause prices to skyrocket -- an impact that would be felt by all commuters, not just former transit riders, he said.

"We really don't have anywhere to put those cars," Mr. Sandvig said.

Much of the additional money spent by former transit riders "doesn't stay in southwestern Pennsylvania," he added. "It leaves," going to oil companies and automobile manufacturers.

Mr. Sandvig is one of nearly 200 people who have registered to speak at a public hearing today on the Port Authority's plan to raise fares Jan. 1 and slash service Jan. 9 if the Legislature does not provide additional funding to cover its deficit.

The hearing runs from 8 a.m. to 8 p.m. at the David L. Lawrence Convention Center.

The authority's shortfall stems from rising health care, fuel and pension costs and declining state aid. The federal government's rejection of Pennsylvania's plan to impose tolls on Interstate 80 caused a $27 million reduction in state funding to the transit agency.

To erase the gap, the authority would reduce service hours by 35 percent, lay off 555 employees and eliminate more than 40 routes, ending all service to at least 50 communities that currently have it.

The base fare would increase by 25 cents, to $2.25 in Zone 1 and $3 in Zone 2. Riders on 13 suburban express bus routes and all Light Rail Transit trips would be charged a "premium" fare of $4.

Nearly all of the three-minute slots for speakers at today's hearing have been claimed, but the authority will have computers set up for others to enter their comments, spokeswoman Heather Pharo said.

The authority also is accepting written comments online at www.portauthority.org or by mail at Port Authority Fare & Service Proposals, Heinz 57 Center, 345 Sixth Ave., Floor 3, Pittsburgh 15222 through 4 p.m. Aug. 31.

The authority board will vote on Sept. 24 to finalize the service cuts and fare increases, but officials have said the actions can be reversed later if the Legislature provides additional funding.

Looking for more from the Post-Gazette? Join PG+, our members-only web site. You'll get exclusive sports content, opinion, financial information, discounts from retailers and restaurants, and more. Our introduction to PG+ gives you all the details.