<Li> A US naval scientist and submarine pioneer, Captain Jacques, was killed getting out of the wrong side of a train at Hadley Wood in 1916 . </Li> <Li> Narrow track centres contribute to "Second Train Coming" accidents at level crossings since it is harder to see the second train--for example, the accident at Elsenham level crossing in 2005 . </Li> <P> When one track of a double - track railway is out of service for maintenance or a train breaks down, all trains may be concentrated on the one good track . There may be bi-directional signalling and suitable crossovers to enable trains to move on to the other track expeditiously (see, for example, the article on the Channel Tunnel), or there may be some kind of manual safeworking to control trains on what is now a section of single track . See single - line working . </P> <P> Accidents can occur if the temporary safeworking system is not implemented properly: </P>

What are the differences between the single-track system and the two-track system