Some asked me how close to the line were signal boxes placed. I don’t know the official figure but at my box at Challow I could stand on the window ledge and step across onto the tender of the engine I was cleaning – that’s what I’d do on a Sunday if I could get the engine driver of a work train to bring his engine to the box. They would if they could because it was more comfortable to sit in an armchair in the signal box. So Challow box was maybe 3ft 6″, from the track. But the engine in this case was on the  Down Releif line, 25 yards from the 20 mph points going out to the Down Main. So trains were passing at 20 mph at most and so maybe the box would be placed closer to the track in  low speed situation.  I have some nice tape recordings of these movements made in about 1960.

Brick signal boxes built immediately alongside the Up or Down Mains or alongside a Releif line such as that between Didcot, Reading and London, where trains passed at perhaps 70 mph (steam days) did not move at all although a loose, sliding, window  might give a ‘crack’ as the wooden frame was smacked back against the outer casing frame by the air wave in front of a fast train. Wooden signal boxes were a different matter altogether. I was familiar with the one at Steventon and that was, I should think,  at the minimum distance from the Down Main and it was always said that  its movement when a fast train passed on the Down was ‘it takes a step backwards’. This was particularly so when the diesels came out. But the tiny, 10ft by 8ft Woodley Bridge box – 8 levers – on the 4-tracks in Sonning Cutting, with which I was also very familiar 60 years ago stood beside the Down Main and I do not recall that moving at all. But I think they’d set it back a bit more than my 3’6″ figure. Clink Road Jc that I worked for a year was an all wooden signal box  beside the Up Main and the flat fronted diesels – D10xx and 50xxx used to come by at a hell of a rate with the bow wave of air in front of them but they had little effect on the structure of the box. A window frame might go ‘smakc’ against its frame.

The box had to be wooden, had to be minimumn distance from the track and had to have fast trains passing to show any reaction to passing trains.