Regular motorway drivers will be familiar with the grammatically ungainly "Keep apart 2 chevrons" notice seen occasionally in conjunction with some arrows painted on the carriageway.
A chevron is a shallow V-shaped (arrowhead) symbol, seen in heraldry and in military rank insignia, often one chevron for the lowest NCO (non commissioned officer), two for say a corporal and three for a sergeant. The chevron can be point up
or down
(RAF Corporal).
The motorway usage is based on the Highway Code advice "allow at least a two-second gap between you and the vehicle in front on roads carrying faster-moving traffic". At 70 mph, the recommended overall stopping distance is 96 metres; the chevrons are painted 40 metres apart and you need to see two chevrons. One of the obvious problems with this is that traffic speed probably varies in different motorway lanes. It might be 60mph in the inside lane and can easily be an illegal 75mph in the outside lane. Additionally, and perhaps more crucially, road/weather conditions are likely to have major influences on safe stopping distances. If it's snowing, the stopping distances are obviously lower; but you wouldn't be able to see the chevrons through the snow, so maybe that doesn't matter. Does this make the chevrons unreliable and even potentially dangerous?
According to trafficsignsandmeanings.co.uk:
Research carried out by the Transport Research Laboratory (TRL) has shown that sections of motorway that have chevrons have shown significant reductions in the number of accidents caused by "close following." The benefits have also been shown to continue for a further 18km beyond a chevron marked stretch.
TRL claims from its research that when chevrons are used on a section of motorway there is a reduction in accidents on the same stretch of road by 56 per cent compared to the same stretch of road before the chevrons were installed.
If this is the case, why not have them on every inch of every motorway? The whole chevron thing is dealt with in section 11.6 Vehicle separation markings of the UK Governments's Traffic Signs Manual chapter 5 of 2018. It tells us "The distance between successive series of chevrons should generally be between 40 km and 55 km." But if you take the above TRL research, shouldn't that be 18km? Unless there has been a later update, it seems that the chevrons are still used on motorways, although in circumstances not stated.
I'd have thought that, if they work, reducing accidents and potentially saving lives, you might just bung them everywhere, at least on motorways. You'd imagine that it's not beyond designers of modern technology to invent a lorry which drives along a motorway lane, painting chevrons every 40 metres. The above Manual says "Road markings are applied using thermoplastic, cold plastic, preformed material or paint." If were up to me, I'd just plonk a 3D printer on the back of a lorry and off we go. You could cover the whole motorway network in a couple of months. Simples.
Presumably they work well enough as a nudge only when they are out of the ordinary. If they were everywhere, we would eventually get used to them and ignore them.
ReplyDeleteOr perhaps we can’t afford the paint. Build HS2 instead.
On a vaguely unrelated note, a colleague in my office got some for speeding on a smart motorway recently and chose to take an online awareness course rather than the points, even though he had already completed one before and apparently you cant be offered that choice more than once.
He ended up with 9 others on a Zoom call, specifically about smart motorways, for 3 hours. The guy leading it spent most of the time barking accusations at various people who may have been looking at their phones or eating. My friend was asked a few questions, got them all wrong and came away no smarter about smart motorways. Bizarre.
….colleague got ‘done’ for speeding…
ReplyDelete