do traffic cops cause traffic jams?

everyone who has ever been to dhaka on a normal workday knows that we have the world’s least enviable traffic jams. on any given day, it can take up to half an hour to travel just a couple of kilometers. my daily commute, which clocks in at only about 7 km each way, takes me anywhere from 20 minutes on a good day, to almost an hour and a half.

urban planning experts complain about the lack of roads. drivers complain about slow-moving rickshaws. passengers complain about the driving skills of others. but everyone seems to agree that one of the major causes of traffic jams is the capacity and activities of traffic police in dhaka.

earlier this year, i decided to test this for myself, as part of a course on econometrics that i was taking at the time. being the pessimist i am, i naturally beleived that, the more traffic police there were on the streets, the more traffic there would be, and therefore the longer it would take to travel a given distance.

i figured that it would be a sufficiently easy model to test, and that getting data would be relatively easy. however, it’s quite a general and basic model in itself, and so there may be flaws in the analysis. the results are quite interesting and informative, but if you would like to bore yourself with the full gamut of econometric analysis, you can see it all here.

the results indicate that, on average, adding another traffic cop to the streets would reduce the average travel time by about 75 seconds. On the flip side, an additional car on the road would increase travel time by 5 seconds.

before we get in to what this could possibly mean, let’s talk about how i did this research. first, i picked a specific route for this study – asad gate to wireless, mohakhali, and the way back, via bijoy sharani and mohakhali rail crossing. this route was selected for several methodological reasons:

  • rickshaws are not allowed to travel on this route, and so the impact of these slow-moving vehicles on traffic jams was controlled. 
  • there are no schools along this route, which means that congestion on this route is also not due to school traffic.
  • parking is prohibited along most of this route, and so most vehicles are supposed to be in motion on this route.
  • this route is one of the most notorious jam-packed roads in the city, particularly in the evenings.
  • there is always generally a high concentration of traffic police on duty along the route.

i collected data on the time taken to traverse the route, the number of traffic cops along the route, and the average traffic gathered at two points during my trip. the last of these was collected at great risk to life and limb: once my car was stopped at the traffic light, i jumped out and counted the number of cars waiting at the light, and then jumped back in to my car once traffic started moving again. data was collected at both morning and evening peak traffic hours. morning rush hour here is defined as between 7 am and 9:30 am, and evening rush hour ranges from 5 pm to 8 pm. to randomize the data, i travelled at different times every day during these two blocks.

what do the results mean? well, to deal with the simple things first, the second result makes sense. given the limited road capacity, more traffic on the streets would obviously lead to more traffic and therefore increased travel time. 

the traffic cop phenomenon is harder to explain though. after all, most of their activity seems to standing at traffic intersections all day, languidly waving to cars to pass or stop. except, of course, if you have an accident or are being mugged. in which case they are most likely to disappear faster than a rabbit after a gunshot.

to explain why this occurs, it’s necessary to extrapolate from our data and use our logic. i surmise that this is because of the fear factor: if there is a traffic cop at the intersection, you are more likely to follow traffic rules and drive carefully. ergo, the more traffic police, the higher the likelihood of following traffic rules.

but that’s a simplistic piece of logic at best, and given the tendencies of bangladeshi drivers, it’s also rather hard to believe. instead, the simpler explanation may be that, as the morning progresses from 7 am onwards, two things happen simultaneously: more traffic cops come on duty, and traffic slowly decreases from the school rush to the commuting rush to the general traffic trends. similarly, as the evening progresses, more and more traffic cops come on for the evening shift while the commuter rush starts to decline.

but are ingenious police shift timings the only cause for this phenomenon? perhaps, but that is quite pessimistic. although travelling down the dhaka streets and watching the activities of the police force would reinforce one’s assumption that they are incompetent, there is also a need to be more objective. i would postulate that there is an extension of the “fear factor” hypothesis: since the primary task of the police is to reinforce the traffic light system, it’s likely that, if there are traffic cops, drivers are more likely to obey traffic lights, thus ensuring smoother flow of traffic and more effective traffic management. thus, there is less traffic, and simultaneously lower travel times.

this research, however, is by no means comperehensive and conveniently ignores several other important variables. for example, it does not take into account how many policemen were actively guiding traffic, as opposed to standing around chatting or seeking bribes while pretending to fine people (i know, gross generalization). similarly, it assumes that all traffic counted is travelling in the same direction, instead of turning or travelling in other routes.

finally, it ignores the fact that there are other underlying reasons for traffic, other than policemen or the number of cars. for example, one of the main reasons traffic jams occur in dhaka is that important intersections are closed off haphazardly across the city, meaning that cars that want to turn at a certain intersection often have to congregate at a limited number of turning points, thus backing up traffic. after all, traffic moves in flowing patterns, and blocking the flow inappropriately can cause it to back up indefinitely. think of water flowing into a bucket through a pipe with lots of holes. if you start plugging up the holes arbitrarily, the amount of water in the pipe will start to increase, until both the pipe and the bucket are flooded. therefore, ignoring traffic mnagement as a primary cause of the traffic jams is virtually impossible.

using these results for policy recommendations along the lines of increasing the number of traffic cops can be dangerous and will probably not solve traffic problems. however, it is undeniable that more cars will cause more traffic, and so traffic reduction must focus on controlling the number of cars or managing them better, so that they don’t clog up the limited pipes that make up dhaka’s streets.


~ by eLeCtRiKbLuEs on December 10, 2008.

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