Road Markings/Double White

Double White Centre lines are commonly found on the British road network, and are commonly considered to mean 'No Overtaking'. However, the correct definition is one of 'No Crossing', albeit with one exception. This means that on roads which are wide enough, it is perfectly legal (although not necessarily always safe) to overtake bicycles, motorbikes and other small vehicles as long as you can stay inside the centre line. On the flip side, it also means that motorists who cut across a white line, however briefly, when taking a bend are breaking the law by crossing the line. However, in almost all circumstances the double white line has been used to prevent overtaking!

The only exception to the no crossing laws are to allow traffic to pass slow moving or stationary vehicles which are blocking too much of the lane for traffic to pass inside the centre line. However, if this is done without due care and caution then legal charges may still be brought against the driver concerned.

Uses

Lane dividers

The most common use of Double white lines is to divide the two lanes on a standard S2 carriageway. They are normally used on sections where overtaking has proved dangerous in the past, so can often be found on short straights to prevent the dangers of overtaking, whilst they may not appear on twistier sections of the same road for the simple reason that no one has ever been daft enough to try and overtake.

In roads with more than two lanes of traffic, double white lines will also appear, with exactly the same meaning as elsewhere. Hence, in an S2+1 road, a double white line will be applied to differentiate which direction of traffic has use of the middle lane. This is invariably the uphill flow, and discourages downhill traffic from using an apparent break in oncoming traffic to overtake. In S4 roads, the double white line can again be applied in the centre to provide two lanes in each direction.

Junctions

Double whites are also used on the approaches to junctions with right turning traffic, so that traffic doesn't try to overtake a slow queue led by a vehicle about to turn right across its path. On busier roads, many of these type of junctions have now been widened to provide a central right turning filter lane, and again double white lines are used to discourage overtaking. In such circumstances, they will normally deviate around the outside of the turning lane, allowing traffic to pull across the striped central area approaching the filter lane. Unless the junction is a crossroads, the opposing traffic has a solid white line throughout.

Double Whites can also be use to control traffic on the approach to give way or stop lines, particularly where the road widens to provide more than one lane. The lines will generally start no later than the point where the road layout changes to provide the additional lanes, and extends to the traffic island (whether physical or painted) at the junction itself.

Other uses

More recently, particularly on wider roads, double white lines have been spaced apart from each other, with a hatched area in between. This tends to be used on roads perceived to be particularly dangerous, to make the lanes narrower and therefore, so the theory goes, drivers will concentrate on driving better. Due to the way these lines are applied, in many cases the cats eyes are set in the line itself, which can in certain conditions give the impression of a dashed white line, albeit with very long dashes and short breaks. This is not the case, and the no crossing rules still apply.

In urban areas, this variant is often used between a series of traffic islands, providing alternating pedestrian crossing points and semi-lanes for turning traffic. As such, it is a type of traffic calming.