Yesterday, I drove north up the M1 to Leicestershire. It was a wet and windy day with driving rain and spray; the road covered for most of the journey in a sheet of water. The overhead matrix signs showed the warning ‘SPRAY SLOW DOWN’ all the way from Luton to Daventry, their flashing amber lights visible far in the distance, each one filling me with the dread of delay. Then the wording changed suddenly. A new and all too familiar warning appeared, ‘QUEUE AFTER NEXT JUNCTION’ with the attached speed, ‘60’. With no visible evidence of a hold up, the traffic continued to overtake me at 70 or 80 miles per hour, even when we past the next matrix, ‘QUEUE AFTER NEXT JUNCTION 40’.
Then, as we traveled under the bridges at junction 16, there were brake lights ahead and the traffic finally slowed. Cars, vans and lorries alike closed up before coming to a halt. We sat there a short while and then set off at an intermittent crawl, stop-start. I saw wagons and cars ahead swapping lanes only to return to their original position a few moments later, minus a few extra drops of diesel and certainly no farther forward. All of a sudden, as if some great barrier had been lifted, the traffic began to speed up and we continued on our individual journeys. All three lanes flowed. There were no signs of an accident, or debris in the carriageway, or broken down vehicles, there were no HATO or police cars; all there was, was a matrix sign that said ‘END’.
The signs had started it all and they had ended it. The question is, why were the signs on in the first place and why, when they displayed a speed of 40, had traffic come to a standstill? The answer to the first part is an assumption. With so much spray and surface water about, there may have been some difficulty with traffic joining the motorway from the busy slip road. It seems significant that the whole thing happened through a junction. The answer to the second part of the question has little to do with the signs and more to do with the way we drive.
I saw a Television documentary a few years ago about aircraft crashes and how, in some cases, pilot error was the cause. More precisely, what caused these disasters was the pilot disregarding information given by the aeroplanes computer, information that would have saved it. One incident occurred in poor visibility when the pilot did not believe the altitude shown on his instruments or the computer’s advice to climb. The aircraft struck a mountain. On another occasion, an aircraft flew in a direction that took it miles off course; it crashed after running out of fuel. The pilot had overruled the navigation computer. The conclusion of the program was that human perception and reality were sometimes out of sync; and we often think we know best, based on experience, even when that experience is flawed.
Most drivers seem to ignore matrix signs and instead rely on what they perceive to be the situation. If the road is clear for the distance they can see, they continue at their normal speed. Only when traffic is actually slowing ahead do they brake, and here lies the problem. Imagine being in a row of cars, say five, all wishing to stay side by side while traveling along a very wide slab of concrete, a runway, perhaps. Car number one is on the left and car five is on the right. At 60 miles per hour they are all together when car one brakes gently. Car two reacts and brakes so as to stay alongside car one, but with a reaction time of about one second the driver has travelled 88 feet at 60 miles per hour while car one has been slowing. Car two must brake a little harder than car one if they are to stay together. Car three must brake harder still and four and five just plain hard. If car one comes off the brake, car five is still braking hard for a further few seconds before its driver realizes and the brakes are released. Naturally, its speed is then below the minimum speed of car one.
This is why traffic comes to a standstill. When the vehicles are one behind another, the distance between each one becomes important. If the gap is too short, braking further down the line can be severe. The matrix signs on the M1 said 40; we stopped. The solution? Forget trying to communicate with the driver; talk directly to the machine. Driverless vehicles and total electronic control; it's coming, and you can see why.
I saw a Television documentary a few years ago about aircraft crashes and how, in some cases, pilot error was the cause. More precisely, what caused these disasters was the pilot disregarding information given by the aeroplanes computer, information that would have saved it. One incident occurred in poor visibility when the pilot did not believe the altitude shown on his instruments or the computer’s advice to climb. The aircraft struck a mountain. On another occasion, an aircraft flew in a direction that took it miles off course; it crashed after running out of fuel. The pilot had overruled the navigation computer. The conclusion of the program was that human perception and reality were sometimes out of sync; and we often think we know best, based on experience, even when that experience is flawed.
Most drivers seem to ignore matrix signs and instead rely on what they perceive to be the situation. If the road is clear for the distance they can see, they continue at their normal speed. Only when traffic is actually slowing ahead do they brake, and here lies the problem. Imagine being in a row of cars, say five, all wishing to stay side by side while traveling along a very wide slab of concrete, a runway, perhaps. Car number one is on the left and car five is on the right. At 60 miles per hour they are all together when car one brakes gently. Car two reacts and brakes so as to stay alongside car one, but with a reaction time of about one second the driver has travelled 88 feet at 60 miles per hour while car one has been slowing. Car two must brake a little harder than car one if they are to stay together. Car three must brake harder still and four and five just plain hard. If car one comes off the brake, car five is still braking hard for a further few seconds before its driver realizes and the brakes are released. Naturally, its speed is then below the minimum speed of car one.
This is why traffic comes to a standstill. When the vehicles are one behind another, the distance between each one becomes important. If the gap is too short, braking further down the line can be severe. The matrix signs on the M1 said 40; we stopped. The solution? Forget trying to communicate with the driver; talk directly to the machine. Driverless vehicles and total electronic control; it's coming, and you can see why.
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