Gauntlet track

Gauntlet track or interlaced track (also gantlet track) is where railway tracks converge onto a single roadbed and are interlaced to pass through a narrow passage such as a cutting, bridge, or tunnel. A frog at each end allows the two tracks to overlap, and the four rails run parallel through the passage on the same crossties, then separate again at the other end. This technique requires only slightly more width than a single track and eliminates the complexities of a switching system since both tracks remain discrete.

Usage and origins

Gantlet tracks can be used to provide horizontal clearance to a fixed obstruction adjacent to a track. Gantlet tracks are also commonly used when a rail line's capacity is increased with the addition of an additional track, but cost or other factors prevent the widening of the bridges.

There are two general arrangements of gantlet tracks, a 'point gantlet', and a 'frog gantlet'. In a point gantlet track the rails for the two tracks typically do not cross. The train taking the gantlet runs over a set of switch points onto the parallel rails, passes through the gantlet area, and passes over another set of switch points to return to the original line. This arrangement is used at the Roselle Park Station referenced below.

In a frog gantlet, one rail crosses over a rail on the adjacent track. A frog is used to provide the flangeway for the crossing tracks. The train taking the gantlet runs over the frog onto the parallel rails, passes through the gantlet area, and passes over another frog to return to the original line. Since there are no points or other moving parts on a frog gantlet track, a train operating on one of the tracks cannot be routed onto the other.

Because two trains cannot use the gantlet at the same time, scheduling and block signals must allow for this restriction.

The term is derived not from "gauntlet" meaning a type of glove, but from the expression "running the gauntlet" (originally "running the gantlope") which means running between two confining rows of adversaries. ["Oxford English Dictionary: Gantlope" (1989)]

Gantlet track can also be used to move a switch away from a heavily trafficked road, as used on the Mannheim tram system.

Gantlet track is typically used for short stretches of track where it is cheaper to provide extra rails than to provide switches and reduce the line to single track.

Dual-gauge track

A similar arrangement is sometimes used to allow trains of different gauges to use the same track. In that case, the two interlaced tracks will have different gauges, sometimes sharing one of the rails for a total of three rails.

Examples worldwide

America

Roselle Park and Union Station on the Raritan Valley Line, in New Jersey, and New Carrollton on the Amtrak Northeast Corridor in Maryland have gantlet track. The gantlet track, with active switches, is used passing high-level platforms, where the track is shared by both passenger and freight trains. The gantlet track allows freight trains the extra clearance they may require, by moving train further away from the platform edge.

The Delaware, Lackawanna and Western Railroad used gantlet track to allow two sets of track to be placed in the centre-line through the Oxford Tunnel in New Jersey.

Australia

The Como River bridge was built as single line in the 1880s. The line was duplicated soon after, except for the bridge. The bridge was fitted with gantlet track, which needs no turnouts, and hence needs no signal box at the far end. The bridge was replaced with a double-track bridge around 1973.

Another example is visible in the tunnel under George Street, Railway Square, as part of the spur which leads from the connection between Sydney's intercity terminus and Redfern. This was a two-track tunnel (one of the oldest on the New South Wales railways) but became gauntlet track when the line was electrified to allow electric locomotive-hauled freight trains to access the former Darling Harbour. There was insufficient clearance in the tunnel to install overhead catenary above both tracks. A single track continues on to the PowerHouse Museum and can be visited as part of the Ultimo Pedestrian Network. This track formerly served the Darling Harbour goods yards and was disconnected from the rest of the corridor which now forms part of the Sydney Light Rail network.

Belgium/Germany

The Botzelaer Tunnel/Gemmenich Tunnel under the "Dreiländerpunkt" ( _en. Three country point) has a special track layout to enable the passage of wide military loads. The double-track tunnel has a third set of rails interlaced with one of the normal tracks. [cite web
last = Desitter
first = Alan
authorlink =
coauthors =
title = German end of the Botzelaer Tunnel
work =
publisher = Picasa Web Albums
date = 2007-05-27
url = http://picasaweb.google.com/alan.desitter/INFRA/photo#5069247836283851234
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accessdate = 2008-03-14] Active points (switches) at each end of the tunnel allow a train to divert along the central track, whilst other trains are blocked by signalling. The third track is rarely in use, so there is no limitation of capacity through the tunnel for standard-sized trains.

Close to where the borders of Belgium, Germany and the Netherlands, the interlaced tunnel section provides an important connection between Germany and the Dutch harbour at Antwerp. After completing the installation in 1991, trains with an oversize loading gauge were rerouted over this line, and the lightly-used (but tunnel-free) secondary line between Stolberg and Welkenraedt (crossing the border at Raeren) was closed to freight traffic. Trains requiring use of the central track must be diesel hauled as electrification only currently reaches the tunnel mouth on the German side to allow for banking. [Railways throughout Europe, [http://www.bueker.net/trainspotting/lines_belgium-germany.php Border lines Belgium - Germany] , retrieved 2008-03-14] [The Brussels Direct Military Railway [http://www.avoe05.dsl.pipex.com/be_montz.htm Aachen West - Montzen - Visé Haut - Tongeren] , retrieved 2008-03-14]

Canada

Gantlet track exists on the Canadian Pacific Railway Bridge across the Rivière des Prairies between Montreal and Laval because the structure gauge is not sufficiently wide for double track. This bridge is used by freight trains of the Canadian Pacific Railway (CPR), the Chemins de Fer Québec-Gatineau (CFQG) (or the [http://www.gwrr.com/default.cfm?action=rail&section=3B6a#Quebec Quebec Gatineau Railway] (QGR)) and by the Blainville-Saint-Jerome Line suburban trains of the Metropolitan Transportation Agency.

Czech Republic

On tram networks, gantlet tracks are used to pass through a narrow passage through a building in Prague's historic Malá Strana and similarly on a narrow bridge in Ostrava. In addition, they are used in various places in Prague and Brno to shift the switch away from high-traffic intersections in order to improve traffic flow.

In the rail system, it is used to overlap metro and normal rail lines; these use the same gauge, but the metro's third rail would otherwise intrude upon the standard railway kinematic envelope.

Germany

In Mannheim, gantlet track is used to shift the switch out of the road to prevent the switch from being driven over by cars and trucks. Mannheim also uses gantlet track to run trams within less space.

In Potsdam, a short section of interlaced track takes trams through the historic Nauener Gate into the old city.

New Zealand

The Interislander rail-ferry ramps at Wellington and Picton have triple gantlet track. At the ferry end of the ramp the outer tracks curve to the left and right to align with the tracks on the ferry rail deck.

The Netherlands

Because of space constraints, Amsterdam's tram network uses gantlet track to increase space for shoppers in the 12 metre-wide Leidsestraat in the city centre. In this busy and otherwise pedestrianised shopping street, the tram stops are located on the bridges over the canals, where more space is available, permitting passing loops that can just accommodate two trams in each direction. Intermediate sections are gantlet track. As service is frequent on routes 2,3 and 5 which use this line, this arrangement often leads to delays. However, on line 10 in Czaar Peterstraat, the situation is reversed, and a short section of gantlet track occurs in a line that is otherwise double, to make room for platforms at the tram stop (see picture). Oddly, in a second radial route, Utrechtsestraat, the passing places on the bridges are served by preset points with single track between them, rather than by gantlet track. Amsterdam has two other short sections of gantlet track: opposite a loading bay in Amstelstraat (route 14) and preceding the points entering the eastern terminal loop outside Centraal Station.

Portugal

The Lisbon tram system interlaces to negotiate one particularly narrow corner in Alfama.

pain

The "Metrocentro T1" tram line of the Seville metro that opened in 2007 features a 300m section of interlaced track along the city's main pedestrian street. The section runs down Avenue de la Constitución, past the Seville Cathedral and World Heritage Site.

United Kingdom

In Britain gantlet track is usually called interlaced track and was often used where street tramways had to pass through narrow streets and even archways in ancient city walls.

* Nottingham Express Transit: just north of The Forest, to avoid a set of points in the middle of a road junction.

* Tramlink in South London: at Mitcham, where a short obstruction prevents double track being used; and at Church St, to avoid a set of points in the middle of a road junction.

* The National Tramway Museum: short section under the narrow Bowes-Lyon Bridge, which causes logistical problems on major running days.

* The Great Orme Tramway: section on the lower part.

Other ideas

Railway curves are generally canted to counter the effects of centrifugal force when going around a curve. The outside rail is raised above the inner, thereby tilting the train inwards as it proceeds around the curve, reducing discomfort to the passengers and minimising the sideways forces to the track.

One problem is that the cant deficiency varies with the speed of the particular train. Freight trains generally travel slower than passenger trains and therefore require less cant to compensate. If there are separate fast and slow lines it is possible to optimise each set of tracks for most likely speed ranges encountered, something not possible without space for two sets of tracks.

An extension of the idea, proposed in 2005, is to build interlaced track through particularly problematic tight curves, allowing both high and low cant compensation within the same trackbed space. High-speed passenger trains would use one pair of tracks and slower, freight traffic the other set. [Freepatentsonline, United States [http://www.freepatentsonline.com/y2005/0145708.html patent #20050145708] , filed 2004-01-07] No track of this type currently exists.

ee also

* Rail terminology (US/UK differences highlighted)

Notes

External links

* [http://www.midtowngreenway.org/programs/transit/Trolley_Study_HTML/4routealignment.htm Gauntlet track] - four rails in Minneapolis (with diagram)
* [http://world.nycsubway.org/perl/show?68158 nycsubway.org] - picture of Gantlet Track at Union Station