For those of us in the US, we're used to seeing roadways with yellow stripes separating traffic traveling against our direction of travel, and white stripes separating traffic traveling in the same direction. Of course, Chapter 3B of the Manual on Uniform Traffic Control Devices requires this. However, I noticed that countries such as England, Japan, Russia, Australia, etc., don't distinguish these features by color. What particular rationales are there for using the color yellow to separate opposing directions of travel on roadway facilities?
As mentioned there are relatively few situations in the UK where this would apply as multi-lane roads tend to have central barriers or other distinctive features.
There is also a system of coloured reflective studs used on major roads which is designed to indicate different types of lane divisions at night.
- White : ordinary lane divisions
- Amber : the edge of the central reservation (the area containing the barrier separating opposing lanes of traffic.
- Green : indicates where slip roads entering of leaving merge with the main traffic lanes.
- Red : indicate the left hand (inside) boundary of the road, either the outside of the hard shoulder (emergency lane) or the edge of the road itself where no hard shoulder is present. Red studs may also be used on some more minor roads.
Virtually all single carriageway roads in the UK have while reflective studs marking the centre line.
On roads without a central barrier double white lines may be used on certain stretches to indicate that traffic may not cross or straddle them (effectively no passing). These are generally found on fast stretches of road with limited visibility where overtaking would be dangerous. In some cases an additional overtaking lane will alternate between directions every few miles.
Yellow lines are generally used in urban area to indicate traffic restrictions especially for parking, waiting and stopping as in double yellow lines and box junctions.
Obviously the road system in north america is significantly different to the UK as distances are much longer.
The most likely reason yellow is used as a color was probably the result of standardization efforts between the 1960s and 1970s (NCHRP Report 484, p8). Since the United States is a very influential country in North America, most other countries bordering them emulated its system to a degree.
Interestingly, the United States has considered moving to an all-white pavement marking system (NHCRP Report 484). The NCHRP (National Cooperative Highway Research Program) conducted a feasibility study for all-white pavement markings, documented as Report 484. At the time the report was conducted, another study was underway (Project 5-18) to determine the effectiveness of yellow pavement markings. The summary as well as the full report can be found on the Transportation Research Board.
Some regions of north america such as the northern US and Canada receive snow. Depending on the snow fall, level of maintenance, traffic, and a few other factors, lines can become obscured to a degree with snow. White lines are much harder to pick out than yellow lines. I personally feel its far more important to know when you are about to accidentally cross over a median line (centre yellow line) and into potentially on coming traffic than it is to accidentally cross over a white line and into an adjacent lane flowing in the same direction.