Clearance car
Encyclopedia
A clearance car is a type of railroad car
in maintenance of way service. Its purpose is to check the clearances around the tracks
and ensure that trains conforming to the railroad's standard loading gauge
or dynamic envelope will not encounter any obstruction. Additionally, by measuring the actual clearances along a route, the railroad can determine whether outsize loads can be accommodated along that route, and the largest size feasible.
Early clearance cars simply consisted of an outline of the system loading gauge attached to a railroad car, which would be towed along the route to ensure the clearances were still sufficient.
Later clearance cars functioned by using physical feelers—rods which extended from the car in all directions which would be deflected back by obstructions. These would be connected to instrumentation which displayed the actual clearance at that point. These feelers have an advantage in that they bounce back and do not break if they do hit something.
More recently, clearance cars using lasers for measurement have come into service. These are generally HiRail trucks—road vehicles with supplemental rail wheels.
The clearance car allowed accurate and speedy measurement of the clearances for a structure. Generally they were only owned by larger railroads; other railroads sometimes leased them for short periods. Some were self-propelled, while others were locomotive-hauled.
Railroad car
A railroad car or railway vehicle , also known as a bogie in Indian English, is a vehicle on a rail transport system that is used for the carrying of cargo or passengers. Cars can be coupled together into a train and hauled by one or more locomotives...
in maintenance of way service. Its purpose is to check the clearances around the tracks
Rail tracks
The track on a railway or railroad, also known as the permanent way, is the structure consisting of the rails, fasteners, sleepers and ballast , plus the underlying subgrade...
and ensure that trains conforming to the railroad's standard loading gauge
Loading gauge
A loading gauge defines the maximum height and width for railway vehicles and their loads to ensure safe passage through bridges, tunnels and other structures...
or dynamic envelope will not encounter any obstruction. Additionally, by measuring the actual clearances along a route, the railroad can determine whether outsize loads can be accommodated along that route, and the largest size feasible.
Early clearance cars simply consisted of an outline of the system loading gauge attached to a railroad car, which would be towed along the route to ensure the clearances were still sufficient.
Later clearance cars functioned by using physical feelers—rods which extended from the car in all directions which would be deflected back by obstructions. These would be connected to instrumentation which displayed the actual clearance at that point. These feelers have an advantage in that they bounce back and do not break if they do hit something.
More recently, clearance cars using lasers for measurement have come into service. These are generally HiRail trucks—road vehicles with supplemental rail wheels.
The clearance car allowed accurate and speedy measurement of the clearances for a structure. Generally they were only owned by larger railroads; other railroads sometimes leased them for short periods. Some were self-propelled, while others were locomotive-hauled.
External links
- MOW equipment page 11 at North East Rails, including several clearance cars.
- Article on the Pennsylvania Railroad clearance car at the Pennsylvania Railroad Technical and Historical SocietyPennsylvania Railroad Technical and Historical SocietyThe Pennsylvania Railroad Technical and Historical Society is a railroad historical society founded in 1974 and organized as a Pennsylvania non-profit corporation and recognized as a 501 tax-exempt organization by the United States Internal Revenue Service.The Society defines its mission as...
's site, written by a former clearance car crewmember.