As hot weather returns, TriMet riders may experience less heat-related delays this season due to improvements our crews made on sections of the MAX system. Trains traveling along the entire MAX Blue Line – between Gresham and Hillsboro – will operate at normal speeds in temperatures up to 100 degrees. The same applies to trains running on the entire MAX Red Line between Portland International Airport and Beaverton Transit Center.
Until now, when temperatures reached 90 degrees, all MAX trains throughout the light rail system were required to go 10 miles per hour slower in high-speed areas above 35 mph. While the trains on the Blue and Red lines will no longer need to slow, the restriction remains on the MAX Green Line between Gateway Transit Center and Clackamas Town Center as well as on the Transit Mall in Downtown Portland, and throughout the MAX Orange and Yellow lines.
When the region experiences extreme temperatures above 100 degrees, all MAX trains on all lines throughout the system will still be limited to traveling no faster than 35 mph for the safety of our riders, employees and equipment. Also, our WES Commuter Rail trains operate at a maximum speed of 30 miles per hour when temperatures exceed 95 degrees as directed by Portland & Western Railroad (PNWR), which owns the trackway. If temperatures soar to 105 degrees, PNWR will suspend WES service and shuttle buses will provide service to WES stations.
During high temperatures, we lower speeds for two important reasons: safety and science. The overhead power wires on the MAX system are made of copper, which will expand and sag as temperatures soar. Also, the rails, made of steel, can swell and bow or kink in extreme temperatures. A one-mile stretch of rail can expand up to a few inches. Operators slow the trains so they will be able to see any such issues and avoid damaging the electrical wires and the pantograph (the arm that transfers power from the wire to the train), which would lead to extended delays for riders.
Because the overhead copper wires expand significantly in high temperatures, we have a system of pulleys with counterweights attached to the wires to keep them taut. The expansion of the wire can make the counterweights reach the ground. To prevent that, our maintenance crews have modified sections of the overhead wire system on the MAX Blue and Red lines using round weights that take up less space than the original rectangular cast iron weights. This allows more room for movement to maintain tension on the wires. They’re also making adjustments based on a formula they developed to best calculate the tension changes needed as temperatures change.
Source: TriMet