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Need a PhD Topic? How about cops in traffic

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Re: Need a PhD Topic? How about cops in traffic

#21

Post by politician »

larrydag wrote: post #4
peter_l_downs wrote: post #2

An interesting question, but I must ask — why is the answer important?

I could see this being possibly useful in traffic "wave" disruption. I've read on the traffic wave theory before and there has been some ideas that if the wave could be disrupted long enough to clear out that it would dissolve and traffic would start to flow again at its normal pace. I suppose that disruption could be done by police cars allowing buffers to build thus disrupting the wave. Can you tell I find this fie…

One of those papers mentioned in the article described "negative traffic" as the gaps in an otherwise saturated segment of road. Vehicles travelling behind the gap tended to have smoother acceleration curves.

I've used this idea to great effect when stuck in traffic by moving into the far left lane, building up a nice gap in front of me, and then cruising at a steady 2-3mph instead of stop-and-go. I've noticed that people generally recognize this as a net-positive and will "follow the leader" with only one or two cheaters (cars which pass me and move into the gap) -- usually the cars immediately behind me.

In order to pull this off, the lane leader needs to maintain a variable length buffer of gap-space in order to prevent their velocity from falling to zero ("stopping").

As the traffic density drops, the gap increases, and you can speed up which ups the average velocity of all of the cars in the lane. Eventually, traffic density will drop down to "normal" conditions at which point cars begin to cheat with increasing frequency until a normal traffic equilibrium is reached (e.g. "not in traffic").

I would love to see an interactive model of this strategy, specifically to figure out the optimum number of lane leaders; less than the total number of lanes, I suspect.

Re: Need a PhD Topic? How about cops in traffic

#22

Post by yummyfajitas »

politician wrote: post #18
yummyfajitas wrote: post #14

Earlier quoted context omitted.

I don't think you need agent models. You can probably study this directly with the nonlinear transport equation (Lighthill-Witham, I think), or one of the more detailed versions (the Rascall model?). All you need to do is impose a police-created boundary condition at x=cop_location(t) instead of solving the pde on free space: velocity(density)|x=cop_location(t) = cop_velocity(t).

Would that model take into account the number of lanes and the lane position of the cop?

It's been a while since I looked, so I'd need to think carefully. But very likely, yes, you could incorporate such things.

What I'd do is in the speed control term V(1-u(x,t)), I'd probably make V vary w.r.t the distance to the cop. I.e., same lane, you'd take something like:

    [V+(V_cop-V)bump(x-cop_position)](1-u(x,t))
Whereas in different lanes, you'd take:

    [V+alpha(V_cop-V)bump(x-cop_position)](1-u(x,t))
where alpha Here, bump(z) is some sort of bump function - 1 near z=0, dropping off as z moves away.

Re: Need a PhD Topic? How about cops in traffic

#23

Post by IanDrake »

>a police car introduces certain mental restrictions which prevent people from behaving how they naturally would.

Just FYI, there's a reason for the mental restriction. If you pass a cop and you're in his jurisdiction and you're going faster than the speed limit you have about a 80% chance of getting a speeding ticket.

80% is the shaky number I came up with based on witnessing 5 occurrences. I was a one driver that got pulled over. I've seen 4 other drivers attempt it and only one didn't get pulled over.

Re: Need a PhD Topic? How about cops in traffic

#24

Post by chadgeidel »

politician wrote: post #21
larrydag wrote: post #4

Earlier quoted context omitted.

I could see this being possibly useful in traffic "wave" disruption. I've read on the traffic wave theory before and there has been some ideas that if the wave could be disrupted long enough to clear out that it would dissolve and traffic would start to flow again at its normal pace. I suppose that disruption could be done by police cars allowing buffers to build thus disrupting the wave. Can you tell I find this fie…

One of those papers mentioned in the article described "negative traffic" as the gaps in an otherwise saturated segment of road. Vehicles travelling behind the gap tended to have smoother acceleration curves. I've used this idea to great effect when stuck in traffic by moving into the far left lane, building up a nice gap in front of me, and then cruising at a steady 2-3mph instead of stop-and-go. I've noticed that p…

I myself try to do that in my lane. Building up a gap so I don't have to use the clutch and can just idle through traffic. I've had varying success with this technique.

Re: Need a PhD Topic? How about cops in traffic

#25

Post by grecy »

IanDrake wrote: post #23

>a police car introduces certain mental restrictions which prevent people from behaving how they naturally would. Just FYI, there's a reason for the mental restriction. If you pass a cop and you're in his jurisdiction and you're going faster than the speed limit you have about a 80% chance of getting a speeding ticket. 80% is the shaky number I came up with based on witnessing 5 occurrences. I was a one driver that g…

I've often tested the theory myself, without breaking the speed limit. If the cop is driving just under the limit, I set my speed exactly on the limit, and overtake if I need to.

Of the ~10 times I've done this, I once got pulled over and abused by the cop for being a "freaking idiot". No ticket.

Re: Need a PhD Topic? How about cops in traffic

#26

Post by TheHegemon »

politician wrote: post #21
larrydag wrote: post #4

Earlier quoted context omitted.

I could see this being possibly useful in traffic "wave" disruption. I've read on the traffic wave theory before and there has been some ideas that if the wave could be disrupted long enough to clear out that it would dissolve and traffic would start to flow again at its normal pace. I suppose that disruption could be done by police cars allowing buffers to build thus disrupting the wave. Can you tell I find this fie…

One of those papers mentioned in the article described "negative traffic" as the gaps in an otherwise saturated segment of road. Vehicles travelling behind the gap tended to have smoother acceleration curves. I've used this idea to great effect when stuck in traffic by moving into the far left lane, building up a nice gap in front of me, and then cruising at a steady 2-3mph instead of stop-and-go. I've noticed that p…

I try to do that as well but it's hard to built up a big enough gap especially in LA where a 'stop' can last up to 15+ seconds. Trying to make a gap big enough without seeming like a complete douche is hard and it makes it that much harder that I have been conditioned to speed up as much as possible.

Re: Need a PhD Topic? How about cops in traffic

#27

Post by gwern »

IanDrake wrote: post #23

>a police car introduces certain mental restrictions which prevent people from behaving how they naturally would. Just FYI, there's a reason for the mental restriction. If you pass a cop and you're in his jurisdiction and you're going faster than the speed limit you have about a 80% chance of getting a speeding ticket. 80% is the shaky number I came up with based on witnessing 5 occurrences. I was a one driver that g…

So actually your number, by Laplace's law of succession (http://en.wikipedia.org/wiki/Rule_of_succession), would be 71%: you saw 4 other instances and you were another instance, so that's 5 instances, and you say you and 3 others were pulled over for 4 pull overs, so in the formula 's +1 / n + 2' we get ' 4+1 / 5+2' or 0.71 or 71%.

Re: Need a PhD Topic? How about cops in traffic

#28

Post by civilian »

huhtenberg wrote: post #20

> How do you model a traffic scenario where certain vehicles introduce more stringent constraints on the vehicles around them that are not purely limited to their physical place on the road? Would this really qualify as a PhD topic these days? Serious question.

I don't have any expertise, but... I think it would.

A dissertation proving that cops on the road slow down traffic might be able to effect public policy. We might be able to get cops off the road during rush hour! We might realize that the benefits of tracking down speeding drivers don't outweight the benefits of having a copless road.

Re: Need a PhD Topic? How about cops in traffic

#29

Post by dll »

IanDrake wrote: post #23

>a police car introduces certain mental restrictions which prevent people from behaving how they naturally would. Just FYI, there's a reason for the mental restriction. If you pass a cop and you're in his jurisdiction and you're going faster than the speed limit you have about a 80% chance of getting a speeding ticket. 80% is the shaky number I came up with based on witnessing 5 occurrences. I was a one driver that g…

Surely this depends a lot on where in the world you are? I regularly break the speed limit while overtaking police cars in the UK and have never been pulled over (but never by much - I figure there's too much work involved to give me a ticket for only going 5 miles an hour over the limit). In fact, I've unintentionally overtaken police while going over the limit in Qatar and the US as well without being pulled over - both places where I'm more fearful of the police than when in the UK.

Re: Need a PhD Topic? How about cops in traffic

#30

Post by IanDrake »

dll wrote: post #29
IanDrake wrote: post #23

>a police car introduces certain mental restrictions which prevent people from behaving how they naturally would. Just FYI, there's a reason for the mental restriction. If you pass a cop and you're in his jurisdiction and you're going faster than the speed limit you have about a 80% chance of getting a speeding ticket. 80% is the shaky number I came up with based on witnessing 5 occurrences. I was a one driver that g…

Surely this depends a lot on where in the world you are? I regularly break the speed limit while overtaking police cars in the UK and have never been pulled over (but never by much - I figure there's too much work involved to give me a ticket for only going 5 miles an hour over the limit). In fact, I've unintentionally overtaken police while going over the limit in Qatar and the US as well without being pulled over -…

True. All observations were in New England.

>I figure there's too much work involved to give me a ticket for only going 5 miles an hour over the limit

True. I typically drive past speed traps at ~10MPH over the limit with no problem. Passing a cop seems to be showing disrespect and I think that's why it'll get you pulled over.

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