(CNN) -- Union workers for San Francisco's transit system ended their four-day strike and returned to work Friday, even though contract negotiations aren't over.
Bay Area Rapid Transit spokesman Rick Rice said things were running smoothly since service resumed at 3 p.m. (6 p.m. ET).
"We pretty much have a normal number of cars on the track at this point," he said.
After negotiations between BART and the unions ended late Thursday, workers returned at 12:01 a.m. Friday and worked through the night and morning to have trains running by 3 p.m., he said.
"People are glad to be going back to work, and I know the riders are thrilled to be able to have the trains running," said Josie Mooney, a spokeswoman for Local 1021 of the Service Employees International Union, one of the two largest union representing the striking workers.
The two sides had three days of negotiations over new contracts, wrangling over the issues of pay and benefits, before deciding Thursday night to allow another 30 days to reach a deal and resume BART service in the meantime.
The talks will pick up again next week.
About 400,000 people use the service daily. With no trains running, BART ran limited charter bus service to accommodate commuters.
BART riders said Friday they were relieved the service was back on line.
"I want to also make sure that the BART workers get their fair share too," rider Tracey Roth told CNN affiliate KGO. "I want to recognize their struggle in it, but also know that it's been tough for everyone."
Commuter Eric Westland told the station he got chills when he learned the trains would be running again.
"The newspaper this morning said it was still on strike, and when I saw the thing in the bus booth that said trains (would be) running at 3, I got goosebumps," he said.
Unions asked for a 21% pay increase. BART initially offered to increase salaries by 4% over four years, but later proposed an 8% increase; that was on top of a 1% increase scheduled to go into effect at the start of the week.
Mooney said part of the problem was that contract negotiations began much later than normal. That didn't allow the two sides a lot of time to reach a deal before the union contract expired June 30.
The extension agreed to Thursday expires at midnight on August 4, she said.
"We hope that we will be able to use the next 30 days to come to a fair and equitable contract for the workers," Mooney said. "Yesterday was spent primarily on extending the (union) contract in order that we have more time to deal with what are extremely complicated issues."
BART is the nation's fifth-largest train system in the United States, with 44 stations in 26 cities that make up the Bay Area, according to the transit authority.
It handles more than 40% of Bay Area commuters, according to CNN affiliate KPIX.