Regional planners calculated the impact on traffic if SEPTA cuts happen. It’s really bad.

An additional 275,000 cars per day would pack the region’s interstates and highways if SEPTA goes through with a proposal to cut nearly half its transit service, new traffic projections from the Delaware Valley Regional Planning Commission show.

Members of the agency’s board of directors were briefed on findings during a meeting on Thursday.

“Imagine if everyone from Pittsburgh decided to visit the region on the same day, and they all drove themselves here — even the children,” said Matt Gates, DVRPC’s associate director for travel trends and forecasts.

“That’s kind of what we’d be expecting,” Gates said. About 300,000 people live in the city of Pittsburgh.

It has the makings of a dystopian disaster, or at least an unpleasant commute for thousands of people.

Average speeds on major routes would drop, some widely used commutes would take much longer, and the number of vehicle miles traveled would increase by 2 million a day in Philadelphia and its four suburban counties. VMT is a measure of all the miles driven in a specific area and time frame.

About 55% of the additional traffic would use arterial, secondary, and neighborhood roads, the analysis says.

SEPTA is facing a $213 million annual structural deficit due in part to pandemic-related ridership reductions and inflationary pressure on labor and materials costs. (Fare evasion doesn’t help matters, costing from $30 million to $68 million yearly, according to SEPTA projections.)

The transit agency released a $1.65 million operating budget on April 10 that included a doomsday scenario of service cuts, along with an average fare increase of 21.5% across the board.

In all, up to 55 bus routes would be eliminated, five Regional Rail lines shut down, and 66 stations closed. Other routes and lines would see reduced frequency of buses and trains.

Those cuts would occur in two phases, this fall and on Jan. 1, without new state subsidies, the transit agency says. If the full menu were enacted, all rail services would stop at 9 p.m. across the SEPTA network early next year.

Dire roadway congestion has been widely predicted as a result of such deep transit cuts, but the DVRPC analysis provides the first publicly available estimates of how bad things could get.

Staff members focused on the morning peak travel period to calculate vehicle speeds and trip times on specific corridors for Thursday’s presentation, Gates said.

For instance, a southbound commute on I-95 from Academy Road to the Vine Street Expressway would take 18% longer than it does today, and traffic would be on average 6.5 mph slower during peak times.

In Chester County, commuting times would increase by 40% on U.S. 202 based on the number of former riders of the Paoli-Thorndale Regional Rail line who would likely drive through the corridor. Paoli is one of five Regional Rail lines that would be shut down.

And an eastbound trip on I-76 from U.S. 422 to Girard Avenue would take 20% longer and traffic would move 7 mph more slowly during the morning peak, defined as 6 to 10 a.m.

That drive currently takes 23.4 minutes in morning peak hours and the average vehicle speed is now 41.4 mph.

Some of the proposed SEPTA service cuts would reduce transit options for people at off-peak times, leading to traffic spikes at other times, including the hours after a 9 p.m. rail “curfew,” Gates said.

Christine A. Reuther, a member of the Delaware County Council, said increased congestion would be devastating for the airport’s cargo business, PhilaPort, and warehouse and distribution companies that need to use I-95.

“People need to know this is a supply chain issue, Reuther said. ”If everything gets tied up, when you multiply that 10% slowdown or that 30% slowdown … by the impact on every vehicle that’s got to get in and out of there, it’s going to be awful."