Leyland being one of those cases where the presents fasts are the newer pair on the newer alignment. Another example was Guide Bridge, where there was a 35 restriction on the fasts because of the curve through the platforms whilst the slows had th straight platforms, and perhaps the classic case that some of us will remember was when Twyford on the GW main line had a 75 on the fasts because these were the newer paid and reverse-curved past the platforms.
Even realigned for fast through running that little wiggle still results in the "Twyford twitch", The secret wake up call for the slumbering high speed Reading commuter (assuming he was lucky enough to get a seat in the evening peak! ).
Indeed and not only there. The realisation also affected a number of resignalling schemes being planned at the time. In reality it wasn't a major safety concern as long as you had excellent sighting at the first caution, which is usually the case on most of the WR, at least the high speed parts.
The Midland Railway (MR) line from Bedford to St Pancras had an even more complex interchange of lines over the years than outlined above. The MR could afford to buy the land for four tracks, but could not afford the cost of laying all four tracks for some years until traffic increases, goods and passenger, compelled them to do so. An Up Goods line was first fitted between Leagrave and Luton in 1875 and gradually extended to St Albans. The Goods lines were doubled to St Albans by April 1894 and onwards to Elstree South by June 1894. (The presently preserved St Albans South box was erected in 1892 in anticipation of the need for more signalling facilities.) The two passenger lines were referred to as such until June 1895 when the new second tunnel at Elstree was opened and the goods line extended through it - at which point from St Albans southwards they were renamed the 'Slow' lines and the passenger lines became the 'Fast Lines' southwards from St Albans. The Goods line remained as such northwards until 1906 when extra platforms were installed at St Albans and Harpenden and the 'Slow' line extended northwards to a junction with the passenger lines just north of Harpenden.
