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Astraist
Master Driver



Joined: Mar 27, 2010
Posts: 209

PostPosted: Mon Jun 06, 2011 9:22 am Reply with quote Back to top

This article relates to subjects that rose in the past, regarding following distance, speeding-issues and my article on road engineering. This article will describe how we as drivers can flow with traffic and make traffic flow with us. Applying it's principles can reduce driving time, decrease risk of crashing (including the car behind us) and reduce gas consumption, pollution and mechanical wear considerably.

The Following distance
Every human being needs some time to react to situations. When first officially measured, reaction times were tested with young athletes who were challenged to sit in front of a redbulb that would occasionally light up, upon which the athlets were ordered to press a button under their finger tips or foot toes. The results wer 0.3 to 0.4 of second, given that the subjects were warmed up, aware of the experiment, with their fingers hovering over the button, and with no need to anaylse the situation. In driving, we need to assume a response time of about one full second.

This response time would mean that we have to maintain a certain following distance from cars ahead so that, when they brake suddenly, we too should be able to react and still stop short of the car ahead. For this, two FULL seconds are considered sufficient. The way to check is simple: Look down at the car ahead and wait till it passes just over some distinct mark on the road itself, and than count "Two one thousand, three one thousand" for two full seconds.

This equation is not obsolute. Like managing our speed, levels of attention, road position and other varients -- the following distance from the car ahead is dynamic and changes constantly. In any case of doubt: When you are not as attentive as you need to be, when the tarmac appears worn, or when the speed is very high -- maintain the following distance of three seconds instead of two. For wet conditions, maintain a general distance of four seconds (and five under said "doubts"). For frozen conditions, maintain a full ten seconds (twelve under said "doubts").

The following gap also helps in achieving smoothness and good milleage. By tailgating another, we block our own visual field and we "ride" on his brakes. This also causes so-called "Shockwave" jams where one driver is tailgating another. The first driver slows down, which makes the following driver slow down much more drastically, creating a small jam behind him. And this brings us to the point of other drivers pushing into your "space" i.e. another driver overtakes you and pushes into the gap you've built from the car ahead.

From observations of various instructors, we've come to the conclusion that it does not occur all that very often and that, when it does occur, it causes an insignificant loss of time. Let's assume a two-hour long journy where an absurd amount of 100 cars pushed their way in front of me. For each car we would have to stray back by one "second", meaning an overall lost of time of less than two minutes, for a completly exaggerated figure of 100 cars!

It's also important to try and maintain a following gap not only from the car in front, but 360 degrees around the car. A safety gap can be created laterally by your position on the road. Most people think they have to drive in the center of the lane all of the time, and they ignore a lot of additional space which is there to be used. In fact, it is the law that states that one should drive on the far right (in the UK, the far left). So, we need to drive on the far right end of the right lane, on the far left end of the left lane, and midway in the middle lane.

This yields various advantages: You have a safe distance from cars that might swerve towards you, you have opened a free passage for bikes and you've made it easier for faster cars to overtake you. Of course this too is dynamic: In a residential road with columns of parked cars on both sides, driving in the middle of the lane is beneficial, and likewise in junctions and before crosswalks. It depends...

You can also try to maintain the gap from the traffic behind. This is done by taking frequent but brief peeks at the mirrors (once every five seconds) and noticing traffic that seems to follow too closely. As a rule of thumb, if you can't see the lights of a private car behind you, it's too close for sure. In highway speeds you even need to see some tarmac between you and it. If you are in doubt whether you are being tailgated or not, simply increase your following distance in front to three seconds again.

If you are sure you are tailgated, try to shake the tailgater off by moving right. If not possible, use the hazard lights to scare him off. If it does not work, try to momentarily flush to the left end of the lane as if to "block" him. If nothing works, your only solution is to drive a bit more slowely, and maintain twice the following distance from the car ahead (four seconds instead of two). You are basically keeping a safety gap for the driver behind too.

A following distance is also relevant when stopped. When coming to a halt before a traffic light or whatever, stop a bit early, so you have a certain "run-off" area in front. Once the car behind you seems to slow down to a stop, consider yourself "covered" and move forward towards the light/car ahead/whatever. Even once covered, maintain a certain distance from a car ahead, so you can see the bottom of it's rear wheels.

This distance has various benefits: It clears out a small, possible run-off area, it clears out a space for bikes to manuver through in traffic, it allows to move forward and aside to clear way for moving traffic (if something fails in your own car) or for emergency service vehicles. Even if traffic behind you is hit and creates a "chain reaction" that hits you too, it will not push you on the car in front.

Stuck in Traffic
What happens in traffic jams? Do we need to know anything to drive in heavy traffic or just crawl along? Yes, there is lots to know about jams. Traffic jams cause lost of time, frustration, pollution, increased gas milleage and wear, as well as rear end collisions. We can do a lot to minimize those issues by helping the traffic around us flow.

You see, traffic jams have a certain mechanism to them. They are essentially a result of a certain "bottleneck" before which the flow of traffic becomes reduced as either the speed of the cars or their amount are increased. This forms a jam and the jam forms "weaves" that go against the direction of traffic: One car "leaps" forward, clearing space for the car behind him to accelerate, only to be stopped not 50 meters later.

This driving style of gas-brakes-gas-brakes is equall to gallons of wasted fuel, as cars have to accelerate from a full standstill rather than from a certain moving speed. It is also the cause for rear-end collisions and for lost of time. Car brakes are roughly five times as strong as their brakes, so the cars will come to a halt at one fifth of the space it took them to accelerate to that speed. So, if the traffic gets stopped for a given period of time, it will take it five times more to regain the speed it carried before the jam.

So, there is a simple solution to all of those problems: Instead of accelerating to 30 and back to 0, drive at a constant speed of 10km/h or so? Just maintain a big following distance from the car ahead and find a pace where you can always stay moving. By doing this you save a lot of gas but you also stop the jam. The traffic behind you is essentially not experiencing a traffic jam, they are only moving slowely (in what is called "congensted traffic"). They too will save gas and also time, but mainly -- they are not likely to ram your rear bumper.

Some main highways are montiored by a control center. The control center supervises dozens of cameras and sensors (weights) in the road surface, which helps them detect any potential of a jam. Upon such an ordeal, they will post notes on digital screens over the road, and also post "updated" speed limits (to which you must legally yield) that reduce speed to a point where the jam will not be formed.

Looking up far ahead also helps. You can look through the rear window of the car in front or above it. By looking further ahead you can see the brake lights of the car in the front of the queue and anticipate the oncoming deceleration. The brake lights would again seem to work like a "weave" where the first driver brakes, making the second driver brake, followed by the third and all the way up to you. This helps to see a forming jam, or to identify a slow-down in a given jam.


Zipping it
One kind of "bottleneck" is formed is areas where traffic from one lane has to merge into another: At interchanges, areas of on-going road constructions, a lane blocked by a collision, etc. There is a method which is a very common practice in Europe, where drivers understand that traffic must "zip" so each driver from the free lane allows just one car from the blocked lane to merge in front of him. Try to follow this discipline in your own personal driving, when you merge and when you let other drivers merge.

Interchanges and junctions are areas which are prone to collisions related to one driver swerving from his lane. We can avoid those situations by a few steps:
- Increase awareness around interchanges/intersections and identify drivers who don't seem to do the same.
- Avoid being in another driver's blind spot: Be either parallel to the car in the near lane, or behind it.
- Place yourself in the far end of the lane, away from any car that might swerve towards you
- Avoid being in between of two cars and try to keep an open "escape route" towards the lane on the opposite side.
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myownworld
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Joined: Jan 06, 2010
Posts: 485

PostPosted: Mon Jun 06, 2011 11:46 am Reply with quote Back to top

"So, there is a simple solution to all of those problems: Instead of accelerating to 30 and back to 0, drive at a constant speed of 10km/h or so? Just maintain a big following distance from the car ahead and find a pace where you can always stay moving. By doing this you save a lot of gas but you also stop the jam. The traffic behind you is essentially not experiencing a traffic jam, they are only moving slowely (in what is called "congensted traffic"). They too will save gas and also time, but mainly -- they are not likely to ram your rear bumper. "

wow! I never knew this was a way to save on fuel in a traffic jam! I'm usually so worried about people honking from behind that I make sure I stay bumper to bumper with the car in front of me. So, you're suggesting that I keep enough distance to keep moving, however slowly, and in this way avoid a dead stop?
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Astraist
Master Driver



Joined: Mar 27, 2010
Posts: 209

PostPosted: Mon Jun 06, 2011 2:17 pm Reply with quote Back to top

Yes. As the car in front leaps forward and stops, and again leaps forward only to stop again, and so ad infinitum, you need to maintain a certain gap from the car ahead, and accelerate much more subtly than the car ahead and to a lesser speed than his, all while looking far ahead in front of him to identify any slow downs in advance. Remember, it goes in weaves of acceleration followed by sudden deceleration after about 50 meters, so instead you need to keep rolling slowely and as steadily as possible. This will save fuel but mainly help the traffic behind you flow and increase your safety.
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myownworld
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Joined: Jan 06, 2010
Posts: 485

PostPosted: Tue Jun 07, 2011 3:34 pm Reply with quote Back to top

Thank you for explaining it so well. Appreciated Smile
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Huoncloutier
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Joined: May 02, 2011
Posts: 24
Location: USA

PostPosted: Wed Jun 15, 2011 12:52 am Reply with quote Back to top

Ya its really useful information. I also appreciate it.
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