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Autogrumble by 'GOM'

2. Why Do They Do That?

I often wonder why traffic engineers do some of the things they do. So many road markings and features seem to be so illogical, but if only somebody would explain the reasoning ...

For example why are there often hatch markings in the middle of the road on the approach to a junction on the right when there is no opposing right turn lane to protect? These have the effect of causing drivers turning right to stay on the left as they slow down which holds up the following traffic. Of course you are perfectly at liberty to drive over the hatch markings as they are normally bounded by hazard lines and not solid lines. In fact it is only an offence to drive over a painted area when it has solid lines containing chevrons and not simple hatch markings - typically where slip roads join dual carriageways and motorways.

The problem is that hatch markings are so overused that you never know whether they are there for a genuine reason or just because some minor bureaucrat thinks they would be a good idea. There are places where you get mile after mile of hatching with hazard lines for no good reason at all. Take the A120 east of Stansted Airport. There are several stretches where there's plenty of room to overtake a slow moving vehicle but the average driver just gets stuck behind because he thinks you can't go into the hatched area. This sort of thing causes unnecessary congestion, and of course it completely devalues the hazard line because you never know if there is a real hazard. Quite apart from that these markings require double the number of cats' eyes and many times the amount of paint compared with simple lane markings.

Some road markings are there to create optical illusions. If there's a wide hatched area in the middle of the road the lanes look narrower so you slow down, don't you? Well maybe the first time, but I haven't noticed my car getting any narrower as I slow down. We used to have a lot of three-lane roads with a "suicide lane" in the middle. On the continent you now get two lanes in one direction followed by a safety zone and then two lanes the other way. In England you just get one lane each way and a wasted hatched area in the middle. If you really want to reduce the lane width why not have cycle lanes on each side?

The most dangerous optical illusion markings are the yellow lines across the carriageway on the approach to some roundabouts on dual carriageways. The lines get progressively closer together so you think you're slowing down less rapidly than you are. I well remember when these were first tried out. I slowed down too quickly and had to speed up again before reaching the roundabout. At the next roundabout I compensated but the line spacing was different and I ended up approaching the roundabout too quickly. After that I tried to shield my eyes from the roadway and concentrate on the the island in the middle of the roundabout. I've now trained myself to disregard these markings altogether. What I want is information, not deception.

When a little psychology would be a good thing the authorities seem to do the exact opposite of what you would expect. If I see a pair of good, clear well positioned speed limit signs I'm happy to slow down to the prescribed speed. On the other hand if I'm subjected to rumble strips, backgammon markings, red tarmac, white gates and big signs painted all over the roadway I feel like doing exactly the opposite of what's intended! If the sign on Remenham Hill flashes "40" at me when I'm doing about 40 I feel like giving it something to flash at me for. Most of the time I refrain!

Why don't SIDs (speed indicating devices) show your speed when you're below the limit? If they did that you'd be able to check your speedometer without breaking the law.

The law requires your speedometer to be calibrated so that it reads between -0% and +10%. So what do you think? "Well, my speedometer's over-reading by 10% so if I go up to 33 in a 30 limit I'll be OK." Or otherwise you drive around at 27 thinking you're doing 30. The actual error depends on factors like tyre wear and pressure so it's usually well below 10%, but if the law required your speedo to indicate between -10% and +0% you'd know that if it said you were speeding you definitely would be!

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Last updated 28th November, 2009