Comment by mixmax | Hacker News Reader

Comment by mixmax | Hacker News Reader

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Interestingly the core problem of highway congestion is that drivers decelerate faster than they accelerate.

An example: Person A slows down a little on the highway for some reason - maybe she sees something on the side of the road, maybe her cellphone goes off, it doesn't really matter. Person B behind her slows down a little as well to keep her clearance, person C does the same and so on. Now person A speeds back up to her original speed (when she is done talking on her phone, watching stuff on the side of the road, or whatever) but she doesn't accelerate quite as fast as she decelerated - this is perfectly normal behaviour - notice it next time you take a trip in your car. Person B does the same thing when she sees person A accelerate and so on. Before long you have a whole row of cars that need to brake because the cars in front of them have decelerated quickly and accelerated slowly. This is what causes most traffic jams on highways.

This is also why a traffic jam moves backwards on the road as time passes.

Yeah, you're pretty right about that. That's one thing I notice driving to school every day. The average speed of cars traveling on the freeway after a highway distraction is significantly lower than the average speed coming into it. I've never understood it. It's as if people have forgotten how fast they were initially traveling. Very frustrating.

Could it be any other way? Could you design a road to induce acceleration and slow deceleration without affecting safety?

A simple and effective way of dissolving a traffic jam is to keep going at the same speed - let me explain:

You see congestion up ahead, and you slow down to, say, 40mph. This creates some room in front of you in anticipation of the inevitable braking. You then drive through the traffic jam at a constant speed with no acceleration or deceleration, and the people behind you will have no choice but to follow (or change lanes which is the weak point of the solution) What you will see at the other end (if you could go back and look) is that you have dissolved the jam because you have prevented people from decellerating quickly and accelerating slowly.

Several people have tried this successfully and it works.

It's really fun when 3 or 4 people all know and do the same thing. It solve the 'weak point' and once or twice I've been part of a 'team' that cleared a jam that way. It's a weird sort of rush.

This reminds me of an old episode of Scientific American Frontiers.

http://www.pbs.org/saf/transcripts/transcript904.htm#5

Thanks for the link. I believe it was this episode that influenced a lot of how I drive (merging, staying slow but consistent in stop-and-go traffic, &c). It should be required watching for new drivers.

Many of the research projects into automated highways concluded essentially the same thing and that average journey times could be significantly reduced, and propagation delays effectively removed, by everyone travelling at near similar constant speed.

The problem however is not everyone will do this e.g. some people simply love to speed, and changing behaviour in people is harder than changing the rules they should follow.

Some of the projects successfully proved the concept in real world usage of the technology, but issues due to insurance (who will be liable in case of accidents) and infrastructure cost seem to be the main barriers at present.

You could make all roads downhill.

In both directions! Where's Escher when you need him? :)

Yes, people are risk-averse.

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