An Amtrak train headed from Richmond to Boston broke down northeast of Baltimore on Sunday, leaving 451 passengers sweltering without air conditioning for more than an hour until a replacement train arrived, a railroad spokeswoman said.

Train No. 88, which left Richmond at 8:35 a.m. and picked up passengers in Washington at 11:25 a.m., became disabled shortly after 1:30 p.m. in Perryville, Md., about halfway between Baltimore and Wilmington, Del., spokeswoman Danielle Hunter said. She said the train’s engine developed a mechanical problem. Without power, the train’s air conditioning system shut down, Hunter said.

Passengers were not allowed off the train for safety reasons, she said. She said the replacement train arrived shortly before 3 p.m.