The double white line, tried out experimentally on the London-Folkstone-Dover and London-Portsmouth roads, is coming to Hertfordshire.

The first road in the county to be treated is the London-Cambridge-King’s Lynn trunk road, and work on one stretch is nearing completion.

Also due for the new system are: “The London-Aylesbury-Birmingham trunk road (A41); the Watford bypass from Colne Bridge to Hunton Bridge, and from Dudswell (north or Berkhamsted) to the Bucks County boundary – and stretched of the A1, A5, A6 and A14.

The new markings use two lines side by side, one for each direction of travel. Each line may be either continuous, where visibility ahead is limited, for example on the approach to a bend or hump, or dotted, where visibility improves after passing a bend or hump. Where there are two lines you need only observe the one nearest to you (when you are on the proper side of the road).

The rules are:

Where your line is continuous you must always keep to the left of the line and must not cross or straddle it.

Where your line is dotted, you can cross it, but it does not indicate it is safe to overtake. It is a warning to take special care.

When sufficient roads throughout the county have been marked, and the lines are familiar to motorists, it will be made a legal offence to disregard them.

[From the Watford Observer of January 9, 1959]