Posted by: wesleyjohnston | May 22, 2013

Musings on Rat Running

Back in the 1990s I was a student at the University of Ulster, Jordanstown campus. The university building is a classic modern structure, consisting of a series of large rectangular blocks. Through the grass outside the blocks the designers constructed a series of paths. In keeping with the style of the building, these paths also followed a grid pattern, running along the sides of the buildings or at right angles to it. Aesthetically it was very tidy.

In a few places the path had to take people from one corner of a rectangular grassy area to the opposite corner. In these cases, the path ran a short distance one way, turned 90° and then ran for a further short distance. What always intrigued me is that in some of these locations, the grass had been worn down to the soil along a line diagonally through the grass between the two points.

What was happening was that pedestrians were choosing what they could plainly see was the direct route between the two points. Although a path existed between these two locations, it followed such a cumbersome route that it was ignored and over time pedestrians created their own path directly across the grass. This is called a desire line, and it exists in all forms of transport. Pedestrians walking across grass simply provide a good example of how in certain situations a desire line can become visually apparent.

Although the eventual outcome of this behaviour was damage to the grass, the creation of a rather untidy mark in the lawn (and perhaps muddy shoes), people went ahead and took the shortcut anyway.

From this example, we can identify two very important principles in transport:

  1. Travellers are inherently rational and will tend to make choices based on rational criteria such as journey time, distance travelled, comfort etc. In our example, the pedestrians choose to cut across the lawn not because they are whimsical or are behaving randomly, but because it is a sensible way to reduce the distance they have to walk.
  2. Travellers are inherently self-interested and will tend to rate the importance of their own journey more highly than the more general needs of society around them. In our example, the pedestrians still cut across the grass even though they know it is causing damage and creating an untidy mark in the lawn.

This example involved pedestrians, but the same principles apply to vehicles. When a road user – such as a car driver or a cyclist – sets off on a journey their aim is usually to get to their destination in a timely manner and in a way that avoids unnecessary expenditure of energy, effort and stress.

Like the architects at the University of Ulster, road planners have carefully classified the road network into A-class main roads, B-class district roads and unclassified local roads, and put up signposts recommending particular routes, in an attempt to get road users to stick to the most appropriate road for their journey.

Such a strategy is also about as effective as the carefully laid out footpaths at University of Ulster. Why? Because road users who make the same journey every day will tend to seek out the most economical route for them, trying alternatives, discarding those that don’t work and repeating those that do, until they settle on the most efficient route to their destination. Because they have the freedom to choose their own route, road users rapidly develop a valuable and intimate local knowledge of the relative time/distance/effort that each possible route involved.

Because they use these local roads each and every day, they become far more knowledgeable about the details of each road than planners in a central office can ever hope to be. They know about the lorry that blocks a particular street at the same time every Tuesday. They know about the pedestrian crossing that causes hold-ups for cars in the ten minutes before school starts. They know the T-junction that’s hard to turn out of. They know about the traffic light which only stays green for a few seconds.

In fact, road users are extraordinarily good at planning routes, far better than any central authority can ever be. If you type a journey you know well into Google’s journey planner, the chances are you will have an opinion about the estimated journey time that it gives. Even the processing power of Google can’t beat local knowledge. In his book The Wisdom of Crowds, James Surowiecki explains why this is the case:

“Under the right circumstances, crowds are remarkably intelligent, and are often smarter than the smartest people in them. Groups do not need to be dominated by exceptionally intelligent people in order to be smart.”

Road users are, in fact, conducting a massive real-time exercise in crowd-sourced route planning. As Surowiecki sets out beautifully in his book, a crowd is not only more intelligent than its individual members, but is often also smarter than the “experts”. Put ten thousand road users into an unknown city and, all motivated by their own self-interest, they will rapidly explore and refine their journeys to the point that, within a few weeks, they will have collectively settled on the most efficient use of road space for them and their vehicles.

Of course, I am not saying that this is the most efficient possible use of road space. Cars, for example, are a rather inefficient use of road space in cities. What I am saying is that from the starting point of having x number of car users and y number of cyclists, etc, these road users will fairly rapidly find the most efficient distribution of road space to accommodate them all.

How does all of this relate to “rat-running”? Rat-running is generally taken to mean vehicles using roads that, from society’s point of view, are not appropriate for their journey. For example, cars that drive along a residential street in order to bypass a busy junction are generally regarded as engaging in “rat running”.

What we have seen both from the example of the pedestrians at the University of Ulster and road users in a city is that road users are generally self-interested, and attach a higher importance to their own journey than the more general interests of society. This is not something peculiar to car drivers, or even travellers in general. It is a phenomenon that is quite fundamental to being human – the desire to put our own interests ahead of those of society as a whole. The phenomenon is classically described as the Tragedy of the Commons: when individuals, acting independently and rationally according to each one’s self-interest, continue to harm a common resource even though they can see the logic in protecting it.

When a driver or a cyclist sees a busy junction ahead, and knowing that there is a side street that bypasses it, they are making a perfectly reasonable, rational, human decision when they choose to take the easier route and nip down the side street. For this reason, I dislike the term “rat run”. Firstly, it creates a subconscious impression that road users who are simply attempting to find the most efficient route for their journey can be compared in some way to rats, which is not helpful. Secondly, it implies that road users who take this kind of route are in some way bad people. This is unfair because “rat running” simply illustrates the inherently self-interested nature of humanity, something that is amply illustrated in numerous other walks of life and is not restricted to driving a vehicle. Being critical of people who “rat run” is simply being critical of something that is inside all of us as part of human nature in general. The criticism could be applied to us all at one time or another.

Now, none of this is intended to say that “rat running” should be tolerated. Since there is ample evidence that the phenomenon does in fact harm local communities, it is also quite rational for road authorities (ie those, who ARE charged with protecting the interests of society) to take steps to prevent it. Once a particular “rat run” becomes inaccessible, road users will, through crowd-sourcing, quickly settle on the next most efficient use of road space – which may, of course involve increased use of other “rat runs”. In a network like the road system, which can be thought of as a very complex grid, it is impossible to eliminate every example of “rat running”, and it would be naive and foolish to try. But it is still rational to attempt to prevent the most harmful examples.

Closing the Barrack Street “rat run” in Belfast a few months ago was an eminently sensible decision for the residents of Barrack Street who faced an intolerable level of through traffic. The displaced travellers seem to have coped okay. The use of fences across residential streets to prevent through traffic movements – provided they have the support of local residents – are one way to tackle the problem. Another approach can be to make a particular route less “desireable” by installing speed bumps, chicanes and other mechanisms that slow down traffic and make a route less popular.

Fundamentally, rat-running is a natural phenomenon that has its origins in human nature, and it is irrational to single out this particular example of human self-interest. Instead, “rat running” should be regarded more neutrally as rational, expected human behaviour which, while it causes problems, can be tackled through a variety of strategies. We should not be too critical of people who “rat run” because, when we do, we are simply being critical of a fundamental human characteristic that is present in us all.


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