The hierarchy of menace among road users and its implications for urban design

A sign in Santa Monica, California instructs drivers to 'Share the road' with cyclists
Cycling infrastructure, Los Angeles style

In recent years a trend has caught on among city planners for redesigning urban spaces in a way that removes traditional features such as kerbs, signage, and light signals. The theory goes that these kinds of structure artificially segregate users of the road and encourage us to respond mechanically to our environment instead of responding attentively to the movements of our fellow citizens. The design approach is known as shared space and it has been pursued with particular fondness by towns and cities in the United Kingdom. (But not just in the UK; see, for instance, this public relations video from Auckland Council in New Zealand, enthusiastically showing off their new shared space.)

There are, however, some serious problems with shared spaces in the way that they have been implemented to date. In short, these spaces tend to create uncertainty at the expense of vulnerable road users: cyclists, the elderly, and the physically and visually impaired (see the resources at the bottom of this post).

My aim in this post is to show that these problems have arisen because the designers have been inattentive to the perceptual strategies being employed by road users (pedestrians, cyclists, motorists). The designers and architects have lacked an appropriate psychology of perception to guide their design decisions. I will suggest that the ecological approach to perception is well-suited to provide the missing theory.

The concept of shared space has recently come under forceful attack in a report by Lord Holmes, a Conservative peer who sits in the UK’s House of Lords. Holmes is himself blind (he is a former Paralympic swimmer) and he is clearly invested in a campaign against shared spaces. His dislike of the concept comes across in almost every sentence of the report, despite its claims to objectivity. The report is based on survey data and it is most effective when Holmes allows his respondents to speak in their own voice:

One respondent summed up the shared space they used as:

“…lethally dangerous. In poor light or glare or shadow, drivers cannot see
pedestrians. Disabled people and those with poor sight or mobility cannot protect
themselves. The idea behind such spaces depends on every user being 100 per
cent able and 100 per cent alert at all times, which just doesn’t happen in real life. I
consider this whole idea to be completely (and criminally) insane.”

One blind user unable to access a local shared space independently said:

“…for people with no sight like myself they are a death trap. I cannot express how
terrible they are and how they make me feel so angry; to think all the people
responsible for them expect us to use it when we cannot see. I use the one in Leek
with my husband and never on my own.”

What comes across in these quotes is a sense that these road users feel they have been excluded from their local surroundings. They have lost their sense of control. (An upshot of this is that assessing whether shared spaces are working effectively cannot simply be a case of going down to the space, setting up a video camera, and observing whether traffic is flowing freely and whether pedestrians are successfully crossing the road. If these respondents are at all representative of a portion of the local population, then the actual traffic patterns will only tell part of the story. What is being overlooked is the fact that some people have simply taken to avoiding the area altogether. The users of the shared space are a self-selecting sample.)

Here is another quote from the report, this one apparently from a cyclist:

In spaces where the lanes are very narrow and traffic movements unclear one
respondent reported a “resulting tendency towards “might is right” rather than the
spontaneous outbreak of courtesy which advocates presume. As a cyclist or
pedestrian, you’re never going to win a contest of might against a car or lorry, so it’s
just intimidating.”

This identifies what is perhaps the central contradiction in the “shared space” approach. All road users are not created equal; there is a hierarchy of menace among us.

The hierarchy of menace

A much-quoted remark by James Gibson, introducing the concept of affordances, reads as follows (Gibson, 1979, p.127): “The affordances of the environment are what it offers the animal, what it provides or furnishes, either for good or ill.” That “or ill” has generally been ignored by researchers, despite the frequency with which it is quoted. If we want to analyse traffic infrastructure in ecological terms we are going to be required to think about that “or ill”.

What the survey respondents to the Holmes report have accurately perceived is that motor vehicles afford danger to cyclists and pedestrians in a way that does not hold in the opposite direction. A truck that pulls into the path of a cyclist affords disaster to the cyclist. But if a cyclist swerves in front of a truck this does not afford serious injury to the truck driver.

This is more than merely a truism because it means that different road users are engaged in different kinds of task (in the sense outlined on Andrew and Sabrina’s blog here). Phenomenally, actors engaged in locomotion are seeking to propel themselves forwards along a path that affords safety to the locomotor (this is described as the “field of safe travel” by Gibson and Crooks, 1938). It is this forward motion, this task, that structures the attentional activity of the actor and that causes certain obstacles to stand out as salient while others recede to the phenomenal background. Obstacles to the actor’s own safe locomotion are of primary concern. And while we should of course all be courteously looking out for each other on the road, it is difficult to monitor the safe locomotion activity of all other road users at the same time, and blind spots and other visual barriers can sometimes make it impossible to do so. To some extent, we have to trust that our fellow road users are looking out for their own safety and that the structure of the road means that they are able to do so.

To propose that all road users should simply share the space, as advocates of the shared space idea do (and as the author of the sign in the photograph at the top of this post does) is to ignore these differences that exist between road users in the tasks that are being engaged in. It is to ignore the relations of danger that obtain between one type of road user and another type further up or further down the hierarchy of menace.

How to build inclusive infrastructure

If we are to be empowered as road users to make decisions about our own locomotion behaviour, then we need to be able to perceive for ourselves that the movements we are engaged in are safe. Designers should abide by the following principle:

Design principle: Make threatening movements perceivable to the threatened

To see why this is the case, consider an example where the threatening movements of more menacing vehicles are difficult to perceive. The photograph below shows a cycle lane in Minneapolis that extends across a junction. For the cyclist travelling straight on in this lane it is necessary to attend to potential motor vehicles attempting to turn right. The right turns takes the vehicle across the path of the cycle lane at a shallow angle. The motorist’s immediate task (the behaviour they perceive themselves to be engaged in, and which is structuring their attention) is to steer the vehicle into the turn. It would be very easy for the motorist, in this situation, to fail to attend to a cyclist travelling alongside, resulting in a turn directly into the cyclist’s path. Consequently, cyclists must check over their left shoulder before proceeding across the junction. But in doing so they take their eyes momentarily off what’s going on ahead, and are thus momentarily unable to monitor for other potentially threatening movements in the junction itself. This is an uncomfortable situation for the cyclist.

A cycle lane in Minneapolis
This cycle lane in Minneapolis is badly designed; cyclists have to look all the way over their left shoulder to check for cars turning right, while also attempting to monitor movements ahead.

The infrastructure that works best is that which allows all road users to easily perceive all the relevant obstacles in their surroundings. This is elegantly illustrated in this short video made by David Hembrow (who blogs at A view from the cycle path), showing a roundabout in the Netherlands that features segregated cycle lanes and pedestrian footpaths.

If various shared space schemes have failed it is because they have created too much ambiguity and they do not provide road users with the structure that would enable them to adequately perceive their own surroundings. If road users do not feel empowered and in control in these spaces it is because they are unable to perceive the threatening movements of vehicles higher up in the hierarchy of menace.

A setting in which motorists can cut across the path of cyclists does not encourage cycling. Far better, from the cyclist’s perspective, that there be segregated infrastructure reserved for bikes. Where motor vehicle traffic has to be crossed it should be crossed on the perpendicular, enabling the cyclist to perceive any threatening movements and respond appropriately. Vulnerable groups of pedestrians, meanwhile, are reliant on light-controlled or, at least, pedestrian-priority crossings which afford them control over the movement of vehicle traffic and allow them to cross safely. Shared space schemes that remove such crossings have failed to provide these road users with an alternative method of control.

These conclusions may seem like nothing more than common sense. Yet the designers of many shared space schemes have evidently failed to accommodate the needs of the road users discussed in this post. This is the case despite shared space advocates’ claims to be informed by “a greater understanding of behavioural psychology” (Hamilton-Baillie, 2008). Perhaps what is needed is a greater understanding of the actual locomotion tasks that different road users are engaged in, along with an understanding of the dangers that must be attended to and the strategies being relied on by actors for taking control of their own behaviour. Only by identifying the sources of danger will it be possible to remove them or mitigate them. An understanding of the tasks that road users are engaged in will only come with a thoroughgoing theory of perception. Gibsonian psychology is well-suited for the job.

Note: I presented some of these ideas last weekend at the International Conference on Perception and Action which took place at the University of Minnesota (hence the photo from Minneapolis). All the talks were videoed. I hope to post a link to the video when it turns up online.




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