BART admits when the weather gets hot, its trains tend to get uncomfortable.
"One third of the cars tend to have air conditioning issues when ambient temperatures rise above 90 degrees," spokeswoman Luna Salaver told Bay City News.
A video that explains what happens is at this link and is embedded below.
The trains are overdue for an upgrade but BART's Linton Johnson said, "There are a lot of other competing needs right now."
For example, BART faces a capital funding deficit of about $7.5 billion over the next 30 years. Johnson said that, among other improvements, BART needs to replace its entire rail fleet.
If you find yourself on a hot train you are supposed to notify the train operator so that one of six roving technicians can address the problem.
The heat can also slow the entire system down when the network of boxes that controls the trains malfunctions. If a box overheats it can cause a stall. That happened earlier this summer. So far that hasn't happened this week.
Caltrain is also affected by the heat. Rails can actually warp and expand in the heat and be damaged by trains' weight. That also happened over the summer but has not happened so far this week.