Dear Irrational (driving fast and police cars)
Dear Irrational,
A practice I often noticed on the I-90 in New York State (Or I-25 where I now live) is that people speed on the highway until they see a police officer with a speed gun (or with flashing lights writing a ticket to some poor driver on the side of the road), and then they slow down and drive at the speed limit for a while.
What I don’t understand is that the probability of two police officers one after the other is very low (lower than the probability of having one), so shouldn’t people speed up after they see a police officer with a speed gun?
Yours truly,
MV
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Dear MV,
This is an interesting observation and although I don’t have data on this, I agree with you that the occurrence of multiple police officers on the highway is most likely negatively correlated. This means that if you see one, you are less likely to see another immediately after. And you are right that this suggests that rationally, people should speed up immediately after passing a police officer.
While the act of slowing down after passing a police officer might be irrational, I suspect that people generally want to be law abiding and don’t want to take too much risk while driving. So seeing a police car serves as a reminder of these two basic ideas.
Here is an experiment that could be fun to do:
In one condition simply and inconspicuously measure speed of passing cars at multiple places along the highway.
In a second condition, do the same but in addition have a visible police car between two of the places where you are measuring speed. The idea being that people will slow down after passing the police-which is your point.
In a third condition we will have a sign that reads “Reminder: the speed limit is 55 MPH. Drive safely.” I suspect that this sign will also reduce speed, but the question is whether it will reduce speed to the same degree as the police car. If it does, then we will know that the speed reduction effect is fully due to the reminder function and not to the fear of being caught (though of course it is possible that they will both work).
Maybe some police department will help us do this.
Irrationally yours,
Dan
My latest book, The Upside of Irrationality, explores some positive and some negative ways that irrationality plays out in our lives.
Of course, I know police officers who pull over to the side with lights on, because they know some people won’t slow down (due to the unlikelihood of there being another cruiser nearby available to pull them over). Then, they ticket these “rational” people.
Thinking that seeing one cop means you are less likely to see another…isn’t that Gamblers Fallacy? Beware, they often run in packs, motor cops like to saturate an area that is usually dictated by a supervisor. Oh and yes, there is a quota in that supervisors mind and if you are under it, you will hear about it. Aren’t we sort of getting into game theory? The cops are playing too.
Birds of a feather flock together.
If you see one police car, there’s no logical reason to think it’s less likely that others aren’t around.
Dear Dan,
I am in the process of reading you book “Predictably Irrational”.
Page 58 discussion about Amazon gift certificate is confusing to me.
Under the following situation I believe you would agree with me.
Assume the neither certificate is “FREE”. One costs $7.00 and is worth $20.00 the second costs $1.00 and is worth $10.00. The better value (profit) is to buy the $10.00 gift certificate. The return on investment is 9 to 1 the other gift certificate return is 13 to 7 or 1.85 to 1.
I would prefer to pay you $1.00 each for 7 certificates buy 7 and have $70.00 of certificates instead of $20.00 of certificates.
Therefore, if the cost is lower than $1.00 (in fact zero) how can buying the $20.00 certificate be the better deal?
Waiting for a response.
Regards,
John L. Morace
Hi John,
2 clarifications
1- people could get at most one and only one certificate
2- When you calculate the returns the rational thing to do is took at differences not ratios. After all you would not want to say that a $10 certificate for $1 payment is better than $10,000 for $1,500
Also — remember that the test for the irrationality is not just based on these two rices but on their comparison to what changes when the price drops by $1
Finally see the appendix as this might clarify things
Irrationally yours
Dan
On the topic of the experiment to see whether people will slow down if reminded to: I believe the third scenario should, instead of a sign reminding people to drive carefully because the speed limit is 55, include a sign that shows a large cut-out of a police car. You can add the reminder info as well, if you wish, but that changes the variable. The cut-out more closely simulates the stimulus that people have conditioned themselves to respond to: the police car; but because it’s a cut-out and cannot possibly give them a ticket if they are speeding, it would more accurately measure whether people are responding to the reminder or to the physical presence of the police.
This scenario lacks two variables to consider.
1. Slowing down speed reduces the danger to the officer performing their duty. Several officers are hit during routine traffic stops each year by speeding vehicles who aren’t stopped. Safety for the officer should be enough to get you to slow down.
2. Radios. You might be able to zoom past an officer on the side, but you won’t be able to outrun an officer who’s called your plate into another officer because you were driving recklessly or above the speed limit.
1. Officer with a speed gun.
In many jurisdictions, a police officer is required to observe you speeding for some distance. So by slowing down, some people are trying to reduce the chance that the cop will start after them. This might be untrue (ie them slowing down would not change the cop’s mind), but it would be a factual error, not a failure of rationality.
2. Slowing down when they see a cop on their side of the road writing a ticket.
The cop might be done with him prey very shortly and be right back on the road chacing the next speeder — and you do not want to be the one.
The idea of using a cardboard cutout of a police car was actually proven to cause drivers to slow down, back in the 1980′s, even when the public was aware that the technique was employed. Another technique that was used in some locales was parking an unmanned police car on the side of the road…very effective in slowing drivers down.
Actually many police departments in my area, put up electronic speed displays – that display your speed on an electronic signs above the speed limit. If you are above the speed limit, your speed flashes until you slow down. There is no cop there, its just to remind you what your speed is – most people slow down when they see there speeds.
cops on roads idle,cops on roads in the process of giving tickets, flashing displays of your personal speed, traditional low visibility areas on the highway where cops sometimes hang, verbal reminders of the speed limit: They all probably slow traffic down..but for how much time do the drivers slow: I bet in decreasing respective distances…I doubt that there is a long enough lasting effect to impact any real outcomes (if there are any real outcomes)