Brain-Teaser 474

From The Sunday Times, 28th June 1970 [link]

Three friends live at the side entrances to a park bordered by three straight roads. Alan’s entrance is on the shortest road, Colin’s on the longest East to West road, and Brian’s on the road of mid length.

Brian and Colin are directly North and South apart across the park, for half the distance they each are by road from Alan. The distance Brian and Colin are apart, plus the length of the three roads, is three miles.

Each entrance is a number of exact yards by road, from any corner of the park, and Alan is as near to one corner as possible.

How far from that corner is he?