A truck cannot bring the same weight to bare on the rails to scrub them properly. I have always believed we should have a purpose built scrubber. In fact, while we still have a few Z1's around (if we still do) in storage, a scrubber 'train" should be made. Remove the cab of # 2 end of one and #1 of the other and and permanently couple use the inner trucks or at least one of them, and mount the scrubbing blocks in lieu of the track brakes, but you can still leave the motors, a vacuum could be in the other car, this would create a relatively "high speed" scrubber that would be able to run at schedule speeds.

It's just a thought bubble but it's been done before elsewhere, why can't we!! properly scrubbed tracks also reduce corrugations, lengthening track life.

Cheers
greg