Everything about Diamond Crossing totally explained
In
U.S. railroad practice, a
level junction (or in the
United Kingdom a
flat junction) is a
railway junction that has a track configuration in which merging or crossing railroad lines provide track connections with each other that require trains to cross over in front of opposing traffic
at grade. The structure is sometimes called a
diamond junction or
diamond crossing in reference to the diamond-shaped center. The two tracks need not be of the same
gauge.
The opposite of a level junction is a
flying junction, where individual tracks rise or fall to pass over or under other tracks. A diamond crossing is also used as a component of a
Double junction.
Risks
Routings must be controlled by
signals and an
interlocking plant, or by an automated Centralized Traffic Control (CTC) system to prevent collisions.
Level junctions, particularly those of fine angles or near right angles, create
derailment risks and impose speed restrictions. The former can occur as the flanges of the wheels are momentarily unsupported and unguided and can slip through the gaps in the rails, and the latter because the assembly contains elements that can break or vibrate loose.
Level junctions are considered a maintenance issue by railroad companies as the inherent gaps tend to be hard on locomotive and rolling stock wheelsets. Switched diamonds partially solve these problems, but introduce some new problems. If possible, diamonds should be replaced by a pair of turnouts.
Examples
Flat crossings are particularly common in the
United States where the lines of one company cross the lines of another company, and there's no particular need for the lines to be connected for through traffic.
In the
United Kingdom, a notable example is
Newark flat crossing where the
East Coast Mainline and
Lincoln to
Nottingham line cross (both double track). Both lines are double-track. This is the fastest flat-crossing UK, with trains travelling north-south allowed to cross the junction at 100
mph (160 km/h). Protection of the junction is controlled by signalling.
At
Rochelle Railroad Park, the double track
UP mainline crosses the double track
BNSF mainline forming four diamond crossings altogether at this location.
Local transport
Flat crossings appear in some urban passenger rail systems, which can cause delays at peak hours as a train heading in one direction may have to wait for trains heading in another direction to clear the junction before it can cross. The junctions leading onto and off from the Loop of the
Chicago El are examples of this problem. The
New York City Subway system mostly uses
flying junctions, but in a few older parts of the system, flat crossings can still cause delays. Examples include the crossing in Upper Manhattan where the uptown (northbound) "3" line departs from the Lenox Avenue line and turns toward the west, crossing over the tracks of the downtown "2" line.
Level junctions are often found on
tram or
streetcar networks where lines cross or split. The
MBTA in Boston has two of these underground on the
Green Line, one where the
E Line departs the central subway just west of
Copley Station, and another where the
C Line and
D Line split west of
Kenmore Station. While the latter crossing rarely causes delays, the former is at an intersection of four lines and cars often have to wait for others to pass at peak hours. Earlier such splits in Boston (such as the disused crossing west of
Boylston Station) were built as flying junctions, but the two level splits were built as level junctions mostly to save money.
Different gauges
Diamond crossings between meter and broad gauge tracks are formed in
Indore and
Ratlam in India.
At
Porthmadog, in
Wales, there's a flat-crossing between the single track
standard gauge Cambrian Line and the narrow-gauge
Welsh Highland Railway (also single track)
Drawbridge crossing
In
Queensland,
Australia flat crossings between
narrow gauge cane tramways and main lines are being replaced by
drawbridges so that the rails of the main line are completely unbroken by gaps or weak spots; this allows the main line speeds to be raised.
Further Information
Get more info on 'Diamond Crossing'.
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