Washington’s Metrorail system, gearing up to transport thousands of passengers to the Mall for the Fourth of July fireworks display, is reporting few problems other than an occasional warm and stuffy rail car, spokesman Dan Stessel said Wednesday.

“It is not a systemic problem,” Stessel said of complaints from passengers that some cars appeared to lack air conditioning.

Rail cars become overheated inside as the day gets warmer and doors open to allow passengers on and off the trains, bringing in hot air along with hordes of riders, Stessel said

As reports come in about cars without air conditioning, Stessel said, “we take them out of service.”

That was little consolation to the approximately 150 passengers heading home Tuesday night on a Green Line train that was unable to move forward shortly after leaving the Prince George’s Plaza station headed towards Greenbelt.

As the train sat idle on the tracks near the College Park Station for about 30 minutes, a group of passengers decided to “self-evacuate,” as Stessel put it, around 6:20 p.m. The outside temperature was still in the 90s.

“I am sure it was very uncomfortable,” Stessel said. A rescue train was en route but once passengers had opened emergency exits and were picking their way along the tracks, Metro had to cut power to both the inbound and the outbound tracks, causing further delays along the Green Line, he said.

The other 150 or so passengers were then escorted off the train by Metro police and other personnel. One passenger was treated for a band was evaluated by Prince George’s County Fire & Rescue.

Stessel said passengers should avoid leaving a train without an official escort whenever possible because of the electrical power coursing through the tracks.

He said service was restored on the Green Line by around 8:30 p.m. Tuesday.