Third rail
Elsewhere in the world, extruded aluminium conductors with stainless steel contact surface or cap, is the preferred technology due to its lower electrical resistance, longer life, and lighter weight.
[3] Because third-rail systems, which are located close to the ground, present electric shock hazards, high voltages (above 1500 V) are not considered safe.
There is also a risk of pedestrians walking onto the tracks at level crossings and accidentally touching the third rail, unless grade separation is fully implemented.
In the United States, a 1992 Supreme Court of Illinois decision affirmed a $1.5 million verdict against the Chicago Transit Authority for failing to stop an intoxicated person from walking onto the tracks at a level crossing at the Kedzie station in an apparent attempt to urinate.
[5] In the event of a collision with a foreign object, the beveled end ramps of bottom running systems can facilitate the hazard of having the third rail penetrate the interior of a passenger car.
Some systems operate dedicated de-icing trains to deposit an oily fluid or antifreeze (such as propylene glycol) on the conductor rail to prevent the frozen build-up.
Locomotives have either had the backup of an on-board diesel engine system (e.g., British Rail Class 73), or have been connected to shoes on the rolling stock (e.g. Metropolitan Railway).
When the shoe slides along the bottom surface, it is less affected by the build-up of snow, ice, or leaves,[3] and reduces the chances of a person being electrocuted by coming in contact with the rail.
Examples of systems using under-running third rail include Metro-North in the New York metropolitan area;[7] the SEPTA Market–Frankford Line in Philadelphia;[8] and London's Docklands Light Railway.
Because of mechanical limitations on the contact to the third rail, trains that use this method of power supply achieve lower speeds than those using overhead electric wires and a pantograph.
Early traction engines were DC motors, and the then-available rectifying equipment was large, expensive and impractical to install onboard trains.
[11] Substations for a DC system will have to be (typically) about 2 kilometres (1.2 miles) apart, though the actual spacing depends on the carrying capacity, maximum speed, and service frequency of the line.
This method has suffered, in isolated cases, from de-lamination (where the stainless steel separates from the aluminium); this is said to have been eliminated in the latest co-extruded rails.
A second method is an aluminium core, upon which two stainless steel sections are fitted as a cap and linear welded along the centre line of the rail.
As originally delivered, the Class 373 units were additionally fitted with 750 V DC collection shoes, designed for the journey in London via the suburban commuter lines to Waterloo.
The trains themselves are no longer fitted with a speedometer capable of measuring the speed in miles per hour (the indication used to automatically change when the collector shoes were deployed).
The cross-city Thameslink service runs on the Southern Region third rail network from Farringdon southwards and on overhead line northwards to Bedford, Cambridge and Peterborough.
On the Moorgate to Hertford and Welwyn suburban service routes, the East Coast Main Line sections are 25 kV AC, with a changeover to third rail made at Drayton Park railway station.
The French branch line which serves Chamonix and the Mont Blanc region (Saint-Gervais-le-Fayet to Vallorcine) is third rail (top contact) and metre gauge.
The RandstadRail project also requires Rotterdam Metro trains to run under wires along the former mainline railways to The Hague and Hook of Holland.
As such, diesel service on Metro-North, Long Island Rail Road, and Amtrak use dual-mode/electro-diesel locomotives (the P32AC-DM and the DM30AC) that are able to make use of the third-rail power in the stations and approaches.
[citation needed] New Jersey Transit also makes use of ALP-45DP dual mode locomotives for operation into Penn Station alongside their normal electric fleet.
The outermost section of the Blue Line runs very close to the Atlantic Ocean, and there were concerns about possible snow and ice buildup on a third rail so near to the water.
Dual power supply method was also used on some US interurban railways that made use of newer third rail in suburban areas, and existing overhead streetcar (trolley) infrastructure to reach downtown.
[citation needed] Some high third rail voltages (1000 volts and more) include: In Nazi Germany, a railway system with a 3,000 mm (9 ft 10+1⁄8 in) gauge width was planned.
For this Breitspurbahn railway system, electrification with a voltage of 100 kV taken from a third rail was considered, in order to avoid damage to overhead wires from oversize rail-mounted anti-aircraft guns.
Third-rail electrification systems are, apart from on-board batteries, the oldest means of supplying electric power to trains on railways using their own corridors, particularly in cities.
This was first tried in Cleveland (1884) and in Denver (1885) and later spread to many big tram networks (e.g. New York; Chicago; Washington, DC; London; Paris, all of which are closed) and Berlin (the third-rail system in the city was abandoned in the early 20th century after heavy snowfall.)
The system was tried in the beachside resort of Blackpool, UK, but was soon abandoned as sand and saltwater were found to enter the conduit and cause breakdowns, and there was a problem with voltage drop.
Bottom-powered railways (it may be too specific to use the term third-rail) are also usually used with systems having rubber-tyred trains, whether it is a heavy metro (except two other lines of Sapporo Subway) or a small capacity people mover (PM).
