The heat is on! How TriMet has worked to speed up MAX and WES trains when temps rise


TriMet’s high heat ‘cheat sheet’ helps riders plan ahead

As temperatures soar in the coming days, TriMet has been working to reduce MAX and WES delays when the thermometer spikes.

Prior to last summer, TriMet crews made improvements to the overhead wire system and track areas along the MAX Blue and Red lines to allow trains to run at normal speeds in temperatures up to 100 degrees. Now, improvements made by TriMet and Portland & Western Railroad mean WES trains will be able to run regularly until 100 degrees, as well.

The science behind heat-related rail slowdowns

Rails are made of steel and can expand by several inches in extreme temperatures. That can causes them to swell and bow, resulting in what is known as a “sun kink”. The rails also get much hotter than the air temperatures. On extremely hot days, the rail can be 20 to 30 degrees hotter than the air.

The overhead power wires on the MAX system are made of copper, which will expand and sag as temperatures soar. Counterweights help keep the wire taut, but in extreme heat the wire expands so much that the counterweights hit the ground, allowing for the sagging. The arm that stretches between the train and the wire, to transfer power to the vehicle, can get tangled in a sagging wire.

System improvements to reduce slowdowns

On the MAX Blue and Red lines, crews have replaced the original rectangular cast-iron counterweights with round ones. This allows more room for movement to maintain tension on the wires. We’ve also made adjustments based on a formula our crews developed to best calculate the tension changes needed as temperatures change. Our crews also have placed rail tie anchors in kink-prone areas of the MAX Blue and Red lines to keep the rail in place.

On the WES line, which runs on tracks owned and operated by Portland & Western Railroad, TriMet worked with the railroad on several improvements to allow trains to travel safely at regular speeds longer. Crews stabilized the rail and the bed underneath them by replacing the ballast, removing vegetation and elevating curves. Those improvements, along with installing Positive Train Control, mean WES trains will not have to slow down until the thermometer hits 100. Previously, they had to slow at 95 degrees. From 2014 through 2018, temps during the afternoon commute reached 95 degrees 32 times.

Extreme heat still requires operating changes for safety

Some temperatures are so extreme that we will need to slow or stop train service for the safety or our riders and to prevent damage to the transit system. So here’s our high heat cheat sheet:

  • MAX
    • 90-100 degrees: Orange and Yellow Line trains, as well as Green Line trains between Clackamas and Gateway, must reduce speeds by 10 mph in higher speed areas. Expect about 15-minute delays.
    • 100 degrees: All lines reduce speeds to no more than 35 mph. Expect up to 30-minute delays.
  • WES
    • 100 degrees: Trains reduce speeds to no more than 40 mph. Expect up to 20- minute delays.
    • 105 degrees: Train service suspended, per PNWR restrictions, and shuttle buses will serve the line. Expect major delays.

Plan ahead

When temps soar TriMet encourages riders to stay hydrated and plan ahead. Check before you head out. All our buses and trains have air conditioning, but when waiting for a vehicle to arrive, stay in the shade if possible. Check or @trimetalerts on Twitter before you head out. You can also sign up for alerts about your bus or train via email or text message at