Clearance car

Last updated
A Washington Metro railcar, originally built for passenger service, later converted to a clearance car. Note the addition of feelers to the car. WMATA Rohr 1028 with locomotive.jpg
A Washington Metro railcar, originally built for passenger service, later converted to a clearance car. Note the addition of feelers to the car.

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. [1]

Contents

Design

A clearance car built to test the ability of impending new locomotives - significantly bigger than their predecessors - to go past platforms and other potential obstructions on the South Australian Railways when the locos arrived in 1926 Loading gauge profile vehicle for South Australian Railways 500 class locomotives, 1926 (NRM 17-336-mb-b21-d15).jpg
A clearance car built to test the ability of impending new locomotives – significantly bigger than their predecessors – to go past platforms and other potential obstructions on the South Australian Railways when the locos arrived in 1926

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.[ citation needed ]

Later clearance cars functioned by using physical feelersrods 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.[ citation needed ]

Subsequently, clearance cars using lasers for measurement have come into service. These are generally HiRail trucks – road vehicles with supplemental rail wheels.[ citation needed ]

Benefits

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.

See also

Related Research Articles

<span class="mw-page-title-main">Rail transport modelling</span> Modeling trains hobby

Railway modelling or model railroading is a hobby in which rail transport systems are modelled at a reduced scale.

<span class="mw-page-title-main">Broad-gauge railway</span> Rail track gauge wider than standard gauge (1435 mm, 4 ft 8 1⁄2 in)

A broad-gauge railway is a railway with a track gauge broader than the 1,435 mm used by standard-gauge railways.

<span class="mw-page-title-main">Railroad switch</span> Mechanism that allows trains to be guided from one track to another

A railroad switch (AE), turnout, or [set of] points (CE) is a mechanical installation enabling railway trains to be guided from one track to another, such as at a railway junction or where a spur or siding branches off.

<span class="mw-page-title-main">Railroad car</span> Vehicle used for carrying cargo or passengers on rail transport system

railroad car, railcar, railway wagon, railway carriage, railway truck, railwagon, railcarriage or railtruck, also called a train car, train wagon, train carriage or train truck, is a vehicle used for the carrying of cargo or passengers on a rail transport network. Such cars, when coupled together and hauled by one or more locomotives, form a train. Alternatively, some passenger cars are self-propelled in which case they may be either single railcars or make up multiple units.

<span class="mw-page-title-main">Track gauge</span> Spacing of the rails on a railway track

In rail transport, track gauge is the distance between the two rails of a railway track. All vehicles on a rail network must have wheelsets that are compatible with the track gauge. Since many different track gauges exist worldwide, gauge differences often present a barrier to wider operation on railway networks.

<span class="mw-page-title-main">Loading gauge</span> Maximum dimensions for railway vehicles and their loads

A loading gauge is a diagram or physical structure that defines the maximum height and width dimensions in railway vehicles and their loads. Their purpose is to ensure that rail vehicles can pass safely through tunnels and under bridges, and keep clear of platforms, trackside buildings and structures. Classification systems vary between different countries, and gauges may vary across a network, even if the track gauge is uniform.

<span class="mw-page-title-main">History of the railway track</span>

The railway track or permanent way is the elements of railway lines: generally the pairs of rails typically laid on the sleepers or ties embedded in ballast, intended to carry the ordinary trains of a railway. It is described as permanent way because in the earlier days of railway construction, contractors often laid a temporary track to transport spoil and materials about the site; when this work was substantially completed, the temporary track was taken up and the permanent way installed.

<span class="mw-page-title-main">Derailment</span> Form of train incident

In rail transport, a derailment occurs when a rail vehicle such as a train comes off its rails. Although many derailments are minor, all result in temporary disruption of the proper operation of the railway system and they are a potentially serious hazard.

<span class="mw-page-title-main">Passenger railroad car</span> Railway car for passenger transport

A passenger railroad car or passenger car, also called a passenger carriage, passenger coach, or passenger bogie is a railroad car that is designed to carry passengers. The term passenger car can also be associated with a sleeping car, a baggage car, a dining car, railway post office and prisoner transport cars.

<span class="mw-page-title-main">Break of gauge</span> Meeting place of different width rail lines

With railways, a break of gauge occurs where a line of one track gauge meets a line of a different gauge. Trains and rolling stock generally cannot run through without some form of conversion between gauges, leading to passengers having to change trains and freight requiring transloading or transshipping; this can add delays, costs, and inconvenience to travel on such a route.

<span class="mw-page-title-main">Defect detector</span> Device used to detect defects on trains

A defect detector is a device used on railroads to detect axle and signal problems in passing trains. The detectors are normally integrated into the tracks and often include sensors to detect several different kinds of problems that could occur. Defect detectors were one of the inventions which enabled American railroads to eliminate the caboose at the rear of the train, as well as various station agents placed along active routes to detect unsafe conditions. The use of defect detectors has since spread overseas to other railroad systems.

<span class="mw-page-title-main">Rail freight transport</span> Train that carries cargo

Rail freight transport is the use of railroads and trains to transport cargo as opposed to human passengers.

<span class="mw-page-title-main">Structure gauge</span> Minimum clearance, height and width of railway infrastructure

A structure gauge, also called the minimum structure outline, is a diagram or physical structure that sets limits to the extent that bridges, tunnels and other infrastructure can encroach on rail vehicles. It specifies the height and width of station platforms, tunnels and bridges, and the width of the doors that allow access to a warehouse from a rail siding. Specifications may include the minimum distance from rail vehicles to railway platforms, buildings, lineside electrical equipment cabinets, signalling equipment, third rails or supports for overhead lines.

<span class="mw-page-title-main">Linkspan</span> Type of drawbridge used for moving vehicles on and off a ferry

A linkspan or link-span is a type of drawbridge used mainly in the operation of moving vehicles on and off a roll-on/roll-off (RO-RO) vessel or ferry, particularly to allow for tidal changes in water level.

<span class="mw-page-title-main">Track geometry car</span> Automated railway track inspection vehicle

A track geometry car is an automated track inspection vehicle on a rail transport system used to test several parameters of the track geometry without obstructing normal railroad operations. Some of the parameters generally measured include position, curvature, alignment of the track, smoothness, and the crosslevel of the two rails. The cars use a variety of sensors, measuring systems, and data management systems to create a profile of the track being inspected.

<span class="mw-page-title-main">Cant deficiency</span> When a rail vehicles speed on a curved rail is high enough to begin tipping over

In railway engineering, cant deficiency is defined in the context of travel of a rail vehicle at constant speed on a constant-radius curve. Cant itself refers to the superelevation of the curve, that is, the difference between the elevations of the outside and inside rails. Cant deficiency is present when a rail vehicle's speed on the curve is greater than the speed at which the components of wheel to rail force are normal to the plane of the track. In that case, the resultant force exerts on the outside rail more than the inside rail, in which it creates lateral acceleration toward the outside of the curve. In order to reduce cant deficiency, the speed can be reduced or the superelevation can be increased. The amount of cant deficiency is expressed in terms of required superelevation to be added in order to bring the resultant force into balance between the two rails.

<span class="mw-page-title-main">Well car</span> Type of railroad car

A well car, also known as a double-stack car, is a type of railroad car specially designed to carry intermodal containers used in intermodal freight transport. The "well" is a depressed section that sits close to the rails between the wheel trucks of the car, allowing a container to be carried lower than on a traditional flatcar. This makes it possible to carry a stack of two containers per unit on railway lines wherever the structure gauge assures sufficient clearance. The top container is secured to the bottom container either by a bulkhead built into the car — possible when bottom and top containers are the same dimensions, or through the use of inter-box connectors (IBC). Four IBCs are needed per well car. In the terminal there are four steps: unlock and lift off the top containers of an inbound train, remove the bottom containers, insert outbound bottom containers, lock assembly after top containers emplaced. Generally this is done car-by-car unless multiple crane apparatus are employed.

<span class="mw-page-title-main">Double-stack rail transport</span> Railroad cars carrying two layers of intermodal containers

Double-stack rail transport is a form of intermodal freight transport in which railroad cars carry two layers of intermodal containers. Invented in the United States in 1984, it is now being used for nearly seventy percent of United States intermodal shipments. Using double stack technology, a freight train of a given length can carry roughly twice as many containers, sharply reducing transport costs per container. On United States railroads special well cars are used for double-stack shipment to reduce the needed vertical clearance and to lower the center of gravity of a loaded car. In addition, the well car design reduces damage in transit and provides greater cargo security by cradling the lower containers so their doors cannot be opened. A succession of larger container sizes have been introduced to further increase shipping productivity in the United States.

<span class="mw-page-title-main">Track geometry</span> Three-dimensional geometry of track layouts and associated measurements

Track geometry is concerned with the properties and relations of points, lines, curves, and surfaces in the three-dimensional positioning of railroad track. The term is also applied to measurements used in design, construction and maintenance of track. Track geometry involves standards, speed limits and other regulations in the areas of track gauge, alignment, elevation, curvature and track surface. Standards are usually separately expressed for horizontal and vertical layouts although track geometry is three-dimensional.

<span class="mw-page-title-main">South African Class Afro 4000</span>

The Passenger Rail Agency of South Africa Class Afro 4000 of 2014 is a South African diesel-electric locomotive.

References

  1. "Close-Clearance Conditions Near Railroad Tracks" (PDF). Iowa Department of Transportation. 6 December 2002.