Gradients in the UK are specified as "1 in N" where N is a number. That means for every N units of length along, the track rises or descends by one unit. Thus a 1 in 100 ascent means that for every 100 metres the track rises by 1 metre (though any unit could be used for both sides of the equation).
Gradients can also be known as grades. To convert from 1 in N, simply divide 1 by N and multiply by 100. For example, 1 in 50 equates to a 2% grade; 1 in 25 equates to a 4% grade.
To give an idea of the effect gradients have on trains, a modern passenger train will not be affected much by anything less steep than 1 in 200. However, a 1 in 50 grade will affect most trains, especially a heavy freight train. A gradient of 1 in 30 is considered extremely steep and will noticeably affect all trains. This is about as steep as UK lines get, and any such gradients will be short. An example of this is the short, 1 in 38 gradient between Exeter Central and St Davids, which causes problems for all but modern DMU stock and HSTs. Also, the Lickey Incline near Bromsgrove (SimSig Gloucester) is so steep, banking locomotives are sometimes required to assist heavy trains from the rear.
Last edited by GeoffM on 15/09/2016 at 03:01