PORTLAND, Ore. -- Ask Oregonians what they think about 100-degree heat and it’s likely you’ll get some cranky responses.

“Not fun. It's going to be hot, somewhat miserable. I'm going to try and stay in the air conditioning and water,” said Mary Houston as she waited for her MAX train.

The heat that's expected to soar past the 100-degree mark this week could mean delays for Houston and other people using public transportation. At above 90 degrees, MAX trains in high-speed areas will slow. But as temperatures go up, speed goes down.

“100 [degrees] is really the threshold for reducing the speeds throughout the system,” said Roberta Altstadt with TriMet.

At 100 degrees, MAX trains across the system will not go faster than 35 mph. Delays of about 15 minutes are expected.

“On the MAX system in extreme temperatures the overhead wires, which are made of copper, can actually sag and the rails that are made of steel can in some areas expand as well,” said Altstadt.

That's why train operators have to slow down.

Altstadt also said the MAX system was built to operate in temperatures that are considered average, and the heat this week is not average.

For people who use the WES trains between Beaverton, Tigard, Tualatin and Wilsonville, temperatures higher than 105 degrees mean trains will stop all together. Shuttles would be used instead.

“Sounds like there is going to be a lot of cranky people,” said Tracy Alan, who often commutes to downtown Portland.

Just last month, the Hawthorne Bridge was stuck in the "up" position for several hours. It was likely due to heat. Don Hamilton with the Oregon Department of Transportation said there's no history of problems with bridges in heat, but staff will be keeping an eye out.

“If we get into this record-setting heat out here, we're going into areas where we're really not certain what we're going to be looking at out there,” Hamilton said.

A Portland Streetcar representative said they’re not anticipating any major complications due to the heat. Streetcars already travel at 30 mph or less. The only concern is that air conditioning units may get overworked. In that case, streetcars that need to defrost would be switched out for another streetcar.

For updates on TriMet delays, click here.