Hi-rail

A hi-rail (sometimes spelled "hy-rail" or "high-rail") is a road vehicle — typically a pickup truck, SUV, or panel van — fitted with retractable steel flanged wheels that allow it to operate on railway track as well as on pavement. The auxiliary wheels are lowered hydraulically when the vehicle reaches a level crossing, locking onto the rail head with the rubber tyres still in contact with the rail to provide traction. The arrangement is used for railway maintenance, signal inspection, weed control, brush cutting, and rapid-response work where rolling a full-sized track machine would be excessive.

The hi-rail is a creature of post-war railroad efficiency: before its widespread adoption, maintenance crews used motorised railcars, pump trolleys, or had to schedule possessions to clear a section for inspection. A pickup with hi-rail gear can self-deploy onto track between scheduled trains, work its way down a few miles, and self-rerail at the next crossing — all without involving dispatch in anything more complex than a routine occupation order. Most Class I railroads now operate hundreds of hi-rails across their MOW and signal departments.

Operationally, hi-rails do not have train-stopping authority and cannot generally trip track circuits the way a locomotive can — they're light enough that the rails see them as just another small load. This means dispatchers must explicitly grant a hi-rail occupation a track-warrant or block before it can foul a main, and the hi-rail crew is responsible for clearing the track in time for scheduled trains. A missed clearance is one of the most common contributors to near-miss reports on North American railroads.

For railfans, a hi-rail in motion is a small and welcome event: it usually signals that something is being inspected, a train has just passed in the opposite direction, or — if it carries cones and traffic equipment on the bed — that a possession is being staged for a crew to follow.