Watford Shed in 1862 was a two-road shed with one through road.
There were only two main lines,
to the north, which eventually became the fast lines and just two main line platforms.
There were no slow lines in 1862, but sidings which became the slow lines are shown alongside the main lines.
The St Albans Branch Line opened in 1858 and this map appears to show a third separate platform, near to the loco shed, for the branch line.
Ordnance Survey Map 1862
