The Science Of Driving And Traffic – the importance of breaking the rules

I wrote this post back in December of 2006 (yes, I think my writing has improved since then) and not much has changed except that the roundabout on Hillsborough Street in Raleigh has been in place for a while now, I drove it several times, and it seems to be fine (though they had to add signs ahead of it to teach the drivers how to use a roundabout) and is certainly successful in eliminating congestion.


Let me state up front that this is not a topic I know anything about, but I have always had a curiosity for it, so let me just throw some thoughts out into the Internets and see if commenters or other bloggers can enlighten me or point me to the most informative sources on the topic. This is really a smorgasbord of seemingly disparate topics that I always felt had more in common with each other than just the fact that they have something or other to do with traffic. I am trying to put those things together and I hope you can help me.

1. Models of Traffic Flow

There are two kinds of people modelling traffic: traffic engineers and physicists. The former use traditional modelling techniques, while the latter indulge themselves in using more esoteric methods, e.g., cellular automata, etc. The traffic engineers, apparently, are not too fond of the models developed by physicists, and I always wondered what the reason for this was and tended to dismiss it as mere professional jealousy and turf-protection. But now I think there is a deeper reason – the two groups do their modelling with two different motivations.

The physicists are testing the math and playing with the computers. Their models are applicable not just to traffic but also to other types of flow, e.g., blood flow. Their main goal is to figure out the conditions that determine when the flow will be smooth, when there will be stop-and-go traffic, and when the whole thing will be ground to a stop.

The traffic engineers, on the other hand, have two goals: smooth traffic flow is one of them, but the other one is to ensure the maximal safety of every individual participant in traffic, something that physics models are barely starting to address. The engineers’ goals are practical – how to build roads in a way that maximizes flow AND maximizes safety. For that, their models have to incorporate not just the behavior of the entire system, but also the behaviors of each individual driver based on the real-life behavior of people operating motor vehicles (as well as cyclists and pedestrians). The physics models have only recently made some baby steps into incorporating realistic human behavior into their models. After all, humans beings behave differently in traffic than red blood cells in blood circulation.

I could not find a study that I remember from a few years back that shows that the “jerks”, those people we hate because they speed and weave in-and-out of lanes, actually contribute to smooth flow – without them, the traffic would be more likely to get congested. Although the speeders only shave off a couple of minutes of their own traveling time, their behavior prevents the blockage of traffic and thus also shortens the travelling time for everyone else.

For (I think) excellent summaries of the current state of traffic modelling I recommend these two articles: Stop-and-Go Science and The Computer Minds the Commuter. Is there anything better or more recent I should read?

2. City Traffic

Most of the traffic flow models I read about deal with the flow and congestion on highways. I could not find that much on modelling traffic of city streets. Such models must exist, though, as someone must have made some calculations when suggesting roundabouts on Hillsborough Street in Raleigh (the street that serves as a northern border of the North Carolina State University campus). For the heated debate about this, check out this excellent blog post and comments and this commentary, just to quickly get up to speed. This discussion has been going on for quite some time now, with quite strong feelings exhibited by the two sides of the issue – the pro and con groups. I have nothing empirical to base my feelings on, but I instinctively aligned myself with the pro-roundabout side. It just felt right. Am I wrong? Why or why not?

3. Car Safety

About a year ago, I have read (in ‘Discover’ magazine, I believe), several people’s essays on the “Future of the Car”. Most wrote about new gizmos and gadgets, more entertainment, and more automation. But one was thinking completely out of the box and I loved it! How to improve safety of the cars, he asked? Not by building bigger, harder and stronger cars with more and more nifty safety features – that is just a never-ending arms-race. Instead, take a lesson from the inflatable gas bags – what makes it useful is its softness, not hardness! So, the author argues, why not make the OUTSIDE of the car as soft as a marshmallow? People would still not want to bump into each other because it affects their own speed and direction, but if such a contact occurs, nobody gets hurt! Brilliant!

4. Geography of Driving Philosophy

I learned to drive back in Belgrade when I was about 18 (min. driving age there), but never bought a car so I did not drive there very much. Still, the driver ed there is a long grueling process, about 40 lessons stretching over several months. During the course, I drove on the highway and in miniscule city streets. I climbed a mountain (and drove back down again on a very narrow twisty road). I drove out in the woods outside the city in freshly fallen deep snow (and my instructor and I helped a couple of other people get their cars out of the ditches). When the city streets were covered with ice one day, my instructor made me go to the hilliest part of town and taught me how to negotiate very steep uphills and downhills on ice.

But, although the driving school was just a couple of blocks away, I had to wait until almost the end of the course until I was allowed (Allowed? Forced – I was terrified!) to try to negotiate Slavija (see picture) – a huge roundabout in the very center of Belgrade where there are absolutely no traffic signs! There are some simple basic rules of traffic applicable to the situation, but most of the rules were actually unwritten rules and all the traffic around it was based on driver-driver negotiation. The way people drive there, everywhere in the country but nowhere felt as palpably as on Slavija, is by such driver-driver negotiations: one part applied psychology, one part hand-and-eye signals.

When I arrived in the United States I had to start driving because there is no other way to get from A to B. And that is when I realized that the driving philosophy is different here – it is not based on negotiations, but rather on strict obedience to much better defined nitty-gritty rules. There are exceptions – driving in Manhattan is more Europen-style in this matter and there may be some other geographical differences within the USA. See this and this for examples.

There is something about this that makes me uneasy. I have a feeling that many people here drive on ‘automatic pilot’, lulled into complacence by a naive expectation that strict following of rules will automatically make them safe. I see it in myself. When I have a sense of flow and a full awareness of my surroundings I drive much safer but that also means that I often buck the rules. After all, the rules are just suggestions, the scaffolding on which we build our driving behavior using our knowledge and experience.

When we drive we make decisions every moment. Most of the time, the decisions we make will be within the rules and laws of traffic. But sometimes, the best decision is to not follow the rules. Safety is the primary concern. When it is satisfied, efficiency comes in as a second concern, followed by wish to minimize wear-and-tear of the car, greater comfort for the driver and passengers, and the fuel efficiency. Blind obedience to rules often does not satisfy either one of these, and when safety is challenged, bucking the rule is the best thing to do.

But, I got a couple of tickets the other year for “rolling through a stop sign” so now I obediently stop. And I discovered that this gives me a false sense of security – I do not pay as much attention to what is really happening in traffic around me. That is unsafe!

What I think is happening is that these stop signs are unnecessary – they should not be there – and when I drive well, somewhere deep inside my mind there is a decision to ignore the sign because it is an obstruction in the way of safe driving. They are inside Southern Village – a little urban village that looks like a toy-set for kids. The fact that the streets are paved at all is kinda nice, and that streets have names is probably useful for the mailman, but traffic signs are totally useless and counterproductive because everyone here drives within the “negotiation paradigm” of driving. Unfortunately, there is a police station in the Village and some cops find it easy to hide in the narrow curvy streets (especially the corner or Parkside and Meeting streets) and quickly gather a bunch of tickets from me and my neighbors without having to go too far [Note; I have moved out about a year ago]. And who is going to argue cognitive science and the physics models of traffic flow with a guy who so clearly enjoys the power of his badge and his gun (and his BLACK uniform – I thought that no police or military force in the world, after the WWII, would be so stupid to use black uniforms of the SS again – as a son of a Holocaust survivor, my first visceral reaction to a black uniform is distrust and fear, not something that makes the cop’s job easier to do)?

So, I was really happy to find that I am not the only one who thinks that most traffic signs are unnecessary or even potentially dangerous. Garry Peterson wrote a great post about this very topic, in which, among else, he quotes from this excellent Wired article:

Hans Monderman is a traffic engineer who hates traffic signs. Oh, he can put up with the well-placed speed limit placard or a dangerous curve warning on a major highway, but Monderman considers most signs to be not only annoying but downright dangerous. To him, they are an admission of failure, a sign – literally – that a road designer somewhere hasn’t done his job. “The trouble with traffic engineers is that when there’s a problem with a road, they always try to add something,” Monderman says. “To my mind, it’s much better to remove things.”

Riding in his green Saab, we glide into Drachten, a 17th-century village that has grown into a bustling town of more than 40,000. We pass by the performing arts center, and suddenly, there it is: the Intersection. It’s the confluence of two busy two-lane roads that handle 20,000 cars a day, plus thousands of bicyclists and pedestrians. Several years ago, Monderman ripped out all the traditional instruments used by traffic engineers to influence driver behavior – traffic lights, road markings, and some pedestrian crossings – and in their place created a roundabout, or traffic circle. The circle is remarkable for what it doesn’t contain: signs or signals telling drivers how fast to go, who has the right-of-way, or how to behave. There are no lane markers or curbs separating street and sidewalk, so it’s unclear exactly where the car zone ends and the pedestrian zone begins. To an approaching driver, the intersection is utterly ambiguous – and that’s the point.

Monderman and I stand in silence by the side of the road a few minutes, watching the stream of motorists, cyclists, and pedestrians make their way through the circle, a giant concrete mixing bowl of transport. Somehow it all works. The drivers slow to gauge the intentions of crossing bicyclists and walkers. Negotiations over right-of-way are made through fleeting eye contact. Remarkably, traffic moves smoothly around the circle with hardly a brake screeching, horn honking, or obscene gesture. “I love it!” Monderman says at last. “Pedestrians and cyclists used to avoid this place, but now, as you see, the cars look out for the cyclists, the cyclists look out for the pedestrians, and everyone looks out for each other. You can’t expect traffic signs and street markings to encourage that sort of behavior. You have to build it into the design of the road.”

Definitely read Distracting Miss Daisy, On “Distracting Miss Daisy” and WHERE THE SIDEWALK ENDS for more thoughts about the idea that too much regulation, and too many signs, are actually making us less safe in traffic:


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