Traffic Calming Devices Can Increase Safety

Traffic calming is the art of slowing, reducing, or diverting auto traffic to improve safety, both in terms of pedestrian or cyclist accidents, and accidents between vehicles. Narrowing streets, through what people are calling a road diet or a skinny street program, actually reduces speeding.

Some literatures looks at 3 E's as key: education, enforcement, and engineering. So while many commentaries focus in tightly on built solutions, the engineering E, the other two are very important also. Community groups can undertake education directly, and also influence their local municipalities to step up enforcement.

Engineered Traffic Calming Measures

There are three major types of built or temporarily installed traffic calming devices in common use:

1. Vertical deflection. In plain English, speed bumps would be the best example. In some places a speed bump is lengthened out to what is known as a speed table, so that a vehicle will have to go slower longer, because the driver knows that the second bump is coming. It's also possible to raise an entire intersection. Instead of a bump as such, a different texture might also be used. Although horizontal rather than vertical, the ridged rumble strips you find beside some highways are examples of a texture change that seems to cause a reflexive slowing or at least heightened attention to what is happening on the roadway.

2. Horizontal deflection. These include traffic circles (now usually called roundabouts), chicanes (in which somewhat difficult to negotiate turns or curves are built into the roadway), and realignment of the road so that it is not as straight. Sometimes center islands are installed where there formerly were none, which forces cars to slow down and swerve around them.

3. Horizontal narrowing. When a road is narrowed for a short stretch, this also requires that drivers slow down for a moment to understand what is happening and thread themselves through a reduced width. These may be called neckdowns or chokers.

More important is the long-term trend toward more narrow streets, which force greater attention. Somehow the neighborhoods with narrow streets and on-street parking on both sides of the street never really have more collisions than the wider streets where everyone has a four-car driveway. That's because of the greater attention required to navigate through the narrow street with the unpredictable parking pattern.

This trend is called skinny streets. Or you might hear the term road diet. In addition to obvious benefits of reducing pavement and therefore stormwater runoff, the narrow street makes it easier to be neighborly across the street, slows traffic, and discourages "through" or "cut through" traffic in a neighborhood.

4. Barrier installation. Anything from an attractive center or side planter to those sawhorses with orange and white stripes that you see in some subdivisions can force traffic to slow down, move, or both. Cul-de-sacs and dead ends may have the effect of slowing traffic, particularly if they are installed at the culmination of a long straight segment of road or street.

The Problem with Engineered Traffic Calming

All of these traffic calming devices are subject to some deterioration of effectiveness over time, as drivers who frequent a certain road or street become accustomed to them. So if you are considering asking for one of these measures in your neighborhood, choose something that it's difficult to adapt to.

For example, I can easily learn where the median planter is and simply adjust my driving, but if I can't see the other side of the roundabout, I may be apt to go through that intersection rather slowly each time.

The second problem with engineered solutions is that they present new dangers, even as speed may be slowed and attention may be refocused on driving. A driver unfamiliar with the area may hit the curb instead of following your fancy chicane! Roundabouts really are confusing if there are more than two streets coming together. The argument is that people will slow down, but not spend extra time in the intersection. From an urban design perspective, however, the roundabout definitely lowers intelligibility (ease of reading and understanding the urban situation carefully).

The Radically Different Solution

If you want traffic to slow down, why not try the softer approaches first? Why not educate people about the much more severe consequences of striking a child at a very slow rate of speed versus at 30 miles per hour? Why not talk to people about a more leisurely lifestyle? Why not create popular destinations closer to home, so that less time is needed on the road in the first place?

Think about making a walkable community, making it easier for developers to propose mixed-use development, and requiring new large developments in your region to follow a new urbanist format?

Incidentally the examples in the paragraph above are instances of the second major approach to traffic calming, which is reducing traffic volume.

Work on helping every household lead a more balanced life, and every individual having less excess aggression that they need to express through their automobile. While your public works department employees weren’t trained in anger management, it’s really worthwhile to re-think how you're approaching particular problems so that you work on the real root cause.

Meanwhile install traffic calming measures if you must, but think carefully about the unintended consequences for a neighborhood.

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