CMR

CMR was a pre-war High speed Monorail service which ran on elevated tracks.

A number of the Monorail Trains can be spotted throughout the Capital Wasteland either on the track or on the ground (due to the track collapsing). The trains however are not explosive and do not show any purpose except for scenery means. The fact that there are so many wrecks and no Monorail stations around the Capital Wasteland is evidence that it was a high speed city to city line within commonwealth boundaries.

Behind the scenes
What the initials stand for is unknown; however, it is most likely to be "Columbia Mono-Rail".