PHILADELPHIA >> Commuters braced for a third day of traffic gridlock in and around Philadelphia as the city’s transit agency urged the union representing about 4,700 striking workers to engage in good-faith negotiations to bring an end to the walkout.

The Southeastern Pennsylvania Transportation Authority said in a statement late Wednesday that a strike should be “an option of last resort,” and when you have one, there needs to be added urgency to “reach an agreement and get back to work.”

SEPTA Board Chairman Pasquale T. Deon Sr. said that on several occasions this week, SEPTA negotiators believed progress was being made, but Deon said the union “brought a halt to negotiations.”

The union had not issued an official response to SEPTA’s statement as of early Thursday morning.

The strike began at 12:01 a.m. Tuesday, shutting down buses, trolleys and subways that provide about 900,000 rides a day. A current cap on union pension benefits and the amount of time off provided to operators between shifts were among the issues on the table.

Frustrated motorists fought traffic gridlock at morning and evening rush hours Wednesday during the second day of the strike.

Highways around the region experienced major backups as thousands of people who normally take city transit used their cars instead.

Regional rail lines experienced delays as a result of increased demand caused by the idling of city buses, trolleys and subways.

The city’s bike-share program was doing a booming business.

Gabby Richards, 23, said she was relieved Wednesday morning to get the last bike available at the stand near her home.

“I’ve been making my plans each day around Uber surge pricing and traffic,” Richards said. “It’s clear that something needs to happen to get people moving smoothly again.”

Uber said it had 41 percent more unique riders during rush hours Tuesday compared with the same day the previous week.

Schools have also been affected, since SEPTA provides rides for nearly 60,000 public, private and charter school students.

The walkout, the ninth since 1975 by the city transit union, is the first since a 2009 strike that lasted six days.

Democratic city leaders working to help end the contract impasse expressed fears of it lasting through Election Day, leaving some residents with little time to vote Nov. 8.

In its statement Wednesday night, SEPTA asked the union to assure residents that, if necessary, they will suspend the strike on Election day if no agreement is reached.