>Why can't a switcher operate on mainline trackage?

They might have a gear ratio or truck design that limits their track speed. At 45 mph even on welded rail standard EMD switcher trucks ride like a bucking bronc.

Most switchers are not equipped with toilets.

Some railroads require leading units in road service to have dynamic brakes in grade territories, or may prohibit roots-blown EMDs in some fire prone territories.


I think the statement being questioned was actually the opposite - without sufficient switchers or 4-axle units, six axle road units have to be used. I know UP is using pairs of SD40-2, SD60, SD60M, etc. on many locals where a pair of small units would have otherwise worked just fine. I also witnessed UP derail a six-axle for the second time on an industry track it had no business being on, evidently a second Geep wasn't available and the crew didn't want/think to split the power. UP by the late 1980s was already requiring all new industry spurs to be built with used 133# rail and be capable of being switched with any six-axle unit.

The railroads would really like to have a one-size fits-all locomotive fleet. The days of assigned locomotive assignments to a division or pool are disappearing.