A while back I mentioned sweeping but didn’t explain what that meant, though you might have guessed it had something to do with checking the alignment. It does – in the interest of safety (no surprises there – you’ll notice that is the predominant theme here), whenever a train hasn’t passed over a section of the alignment in several hours, the first train through that area is a sweep train. The sweep trains run at lower speeds to do a safety check on the alignment.
This is not a sweep train picture, or even a train operating before sunrise. It is, however, a train operating under low lighting and I’m going to say that’s the next best thing. I have no directly relevant photographs for this post.
Under normal operating conditions, the regular sweeping is done by the first train every morning through each area of the alignment. This is built in to the runs for those trains:
And here’s that first Yellow Line on the TriMet timetable – the sweep train takes 19 minutes to get to Gateway and then another 20 minutes to get to Rose Quarter, but the Blue Line that leaves Cleveland at 4:06 (and all the ones after it) will take 17 minutes from Ruby to Gateway and then 15 minutes from Gateway to Rose Quarter. Those trains can travel at full speed once the alignment has been swept.
Sweep speed is 25 mph or the posted speed limit, whichever is less – so the sweep train from Rose Quarter down 5th Ave to the Jackson turnaround at PSU is going to do 15mph, not 25. Point of trivia – 25mph is the slowest speed a train can go down Burnside (where the speed limit is 35mph) and still make all of the pre-empts before they time out.
In the event of sweeping after an emergency – such as an earthquake, as mentioned in the other post, it’s reasonable to expect that Control will ask for restricted speed in the sweep trains rather than the standard 25mph. Restricted speed for MAX trains is 20mph or the posted speed, whichever is less, but always at a speed that would allow the operator to stop within 1/2 their sight distance.