and helped develop tram lines in New York City and Paris. The invention of grooved rail enabled tramways to be laid without causing a nuisance to other road users, except unsuspecting cyclists, who could get their wheels caught in the groove. The grooves may become filled with gravel and dirt (particularly if infrequently used or after a period of idleness) and need clearing from time to time, this being done by a "scrubber" tram. Failure to clear the grooves can lead to a bumpy ride for the passengers, damage to either wheel or rail and possibly derailing. Girder guard rail The traditional form of grooved rail is the girder guard section illustrated below. This rail is a modified form of flanged rail and requires a special mounting for weight transfer and gauge stabilisation. If the weight is carried by the roadway subsurface, steel ties are needed at regular intervals to maintain the gauge. Installing these means that the whole surface needs to be excavated and reinstated. Block rail Block rail is a lower profile form of girder guard rail, where the web is eliminated. In profile it is more like a solid form of bridge rail with a flangeway and guard added. Simply removing the web and combining the head section directly with the foot section would result in a weak rail, so additional thickness is required in the combined section. Prefabricated grooved rail A modern version of the grooved block rail has a lower mass and is inserted into a prefabricated spanning concrete girder such as the LR55 without web but fully supported by noise reducing polyurethane grout or a girder rail such as P-CAT City Metro is embedded. The prefabricated units if used with ultra light trams can be embedded into existing road base with possibly a reduced requirement for underground services diversions. Track gauge Electrification Electrification needed other developments, most notably heavier rails to cope with electric tramcars weighing 12 tonnes rather than the 4 tonne horse-drawn variety; switching points, as electric trams could not be pulled onto the correct track by horses; and the need for electrical connections, to provide the return path for the electric current, which was usually supplied through an overhead wire. Conduit and stud systems In some cities where overhead electric cables were deemed intrusive, underground conduits with electrical conductors were used. Examples of this were New York, Washington DC, Paris, London,