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> A sensible algorithm would let the platoon pass first. You're taking an example of a sub-optimal local solution and claiming that is proof that the global so
by asynchronous13 10y ago
> A sensible algorithm would let the platoon pass first.
You're taking an example of a sub-optimal local solution and claiming that is proof that the global solution is sub-optimal. That does not follow.
It could easily be, taking your example, that the platoon of 5 cars must stop at some future light, and the delay for 1 car is the smallest delay available for those cars. Therefore, stopping for the 1 car reduces the platoon's total travel time. As the driver, it's easy to think that was dumb because you'll never see the 15-car wait that was avoided by stopping early for 1 car.
Essentially, you are claiming that a greedy algorithm for traffic would always find the globally optimal solution (which we know is not true).
- barrkel 10y agoWalter isn't arguing for a greedy algorithm. He's giving an example of a local inefficiency and a mitigation. Lots of local inefficiencies add up to a global inefficiency. Illustrating a global inefficiency in itself isn't feasible in an anecdote. Thus I think your argument by assertion isn't possible to refute: you can bring up "local inefficiencies don't necessarily mean global inefficiencies" to dismiss all arguments that the current system is less than optimal. Me, I've been stuck at traffic lights for 5 minutes at 2 in the morning, with no traffic whatsoever around. A very local algorithm would be highly preferable at that time of night, assuming usual (i.e. very little) traffic at that hour. It's an extreme example, yes: but there does exist a range of traffic patterns between the small hours of the morning and rush hour, and the same amount of global optimization effort is not applied to all hours, for obvious reasons. Something that could analyse the traffic using cameras and sensors and optimize wouldn't have to be paid extra to work late at night.
- asynchronous13 10y agoSeveral cities take the even simpler approach of having lights that change from timed cycles to blinking red/yellow after a certain hour.
- WalterBright 10y agoCars stopping and then starting again costs time, money, fuel, wear & tear, pollution, etc. It's far from an efficient solution.
- douche 10y agoMight not apply where you are, but in my state, if you sit at a red light for that length of time, with no traffic coming the other way, it is legal to ignore the light and go anyway - basically treating the light like a four-way stop sign.