Sentence:  Page 19 / : The reason for this is, that as in these cases there are obstructions in the <WSD>four foot</WSD> which might become foul of wheels of stock [...] / Page 48 / : For ‘ E ' and ‘ F ' switches the key jaw is provided on the inside of the four-foot in the 1.P. and 2.P. chairs, as in these chairs there is not room between the switch and stock rails [...] 
Meaning of the word marked with <WSD> tags:  the space between the rails on a standard gauge railway line.