A road-rail vehicle is a vehicle which can operate both on
rail tracks and a conventional road. They are also called hi-rail, from highway
and rail, or variations such as high-rail, HiRail, Hy-rail, etc.
They are often converted road vehicles, keeping their normal
wheels with rubber tires, but fitted with additional flanged steel wheels for
running on rails. The rail wheels are raised and lowered as needed.
Purpose-built road-rail vehicles also exist.
Road-rail technology is believed to have been developed by
Fairmont Railway Motors in the 1940s to improve flexibility of vehicle use.
Fairmont's key product, motor section cars, limited the ability for maintenance
crews to travel. Fairmont was bought by Harsco in the late 1980s.
Such vehicles are normally used for railroad right-of-way
maintenance during engineering possessions of the line. They can be driven on
roads to near the site and then convert to rail vehicle for the final journey
to the worksite. This avoids the complex maneuvers that would be associated
with a road vehicle accessing the worksite if the worksite is not near a road.
Since they are normally converted road vehicles, they would not fare well in a
collision with a heavy rolling stock and therefore can normally only drive on
rail tracks under an engineering possession. They are generally designed to be
insulated, thus they do not activate track (signaling) circuits although some
rail operators, normally those operating remote lines without boom gates etc.
prefer them to be non-insulated so that they are detectable by train safety
systems.
Self-propelled maintenance vehicles for maintenance of the
track and for shunting wagons are much more convenient to use if they can
transfer to the road to reposition or otherwise get out of the way. Because
relatively light loads are involved, the problems plaguing the Road
Transferable Locomotive are avoided.
An example would be a forklift truck fitted with railway
wheels and a coupling with which to shunt a wagon or two.
In Belgium, the company UCA bvba has been constructing
rail/road vehicles since 1981. UCA started with converting WF-trac and MB-trac
for rail traction uses. They built rail car movers, shunting locotractors and
other rail/road vehicles. Best known is the UCA-TRAC, based on the chassis of a
JCB Load-All (UCA-TRAC B) and Fastrac (UCA-TRAC F). The UCA-TRAC provides
traction through its rubber wheels.
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