Confederacy of a Dunce - Traffic calming

Friday, July 01, 2005

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Numerous different techniques are being used to manage (or mismanage) the flow of traffic around London; I pass so many different varieties on my (~5.5 mile) bike commute I thought I'd take a few minutes to describe the different varieties. Most common is the speed bump. Although I haven't counted them (mainly because I haven't exactly settled upon a regular route) my previous commute included about 70 speed bumps of various types. As it turns out the different types are explained in great detail on sites like this one (where speed bumps are within the "vertical deflection" category), and ranted against on sites like this and this.

Speed humps are the most common sort I encounter (distributed across just about all of the back roads I follow wherever possible), distinguished from other sorts by extending all the way across the road. For motorized traffic, the spacing between them seems to be the biggest issue: the closer they are together, the greater the reduction in vehicle speed (and the greater the impact on larger vehicles that bounce over them -- especially ambulances [one of the big arguments against humps of this sort is that ambulances are forced to slow down, thus increasing response times {and transit-to-hospital times}]). As a cyclist my biggest concern is instead the angle of impact: a sinusoidal hump is much smoother to ride over than a "standard" hump (i.e., one which rises at a sudden angle). The latter can be incredibly jarring to run into (just like hitting a small curb/kerb), especially when the adjoining road surface has sunk or deteriorated. This depends on the neighborhood, and the amount of heavy traffic.

One solution to the concerns for large motor vehicles is the plateau. In its simplest form the plateau is just a longer-than-normal (wider-than-normal?) speed hump with a flat surface on the top (also known as a "speed table"). This apparently prevents some of the "bounce effect" on motor vehicles; the issues for cyclists are the same as for speed humps (it all depends on the quality of the transition from the road surface to the edge of the plateau). These are especially common in intersections: most intersections in our neighborhood has recently been converted into fairly elaborate brick plateaus, although they've already been scarred by fast-moving cars (which hit the not-at-all sinusoidal edge of the raised brick section with a loud kerthump, and many of which seem to spew oil as a result).

Yes another alternative is the speed cushion. This is like a speed hump but with gaps to allow cycles (or the wheels of ambulances) to zoom right by without any vertical deflection whatsoever. Sounds like a great solution to emergency vehicles and cyclists alike, but in practice, this seems to provide even more danger, as car drivers tend to swerve so as to place at least one set of wheels in the "no vertical deflection" area (where there may or may not be a bicycle). Somehow I always seem to be riding over speed cushions in order to avoid being run over.

Another class of vertical deflection traffic calming measures is the "uneven road surface" like rumble strips and jiggle bars. Fortunately I don't experience any of these in my daily commute, as these can be really nasty to a cyclist. They're better suited as warning devices on high-speed roads (motorways and the like), not very well suited to any sort of residential areas as they're incredibly loud.

And that's just vertical deflections. I haven't even gotten to horizontal deflections (chicanes and half-chicanes), road narrowings, false one-way systems, islands, gates, speed cameras, pseudoroundabouts, or any of the futile attempts to keep pedestrians alive. Anyway, there are numerous official UK documents on traffic calming here, including the official traffic calming regulations, and just about anything else (PDF about traffic calming in Bird

bike

Friday, July 01, 2005 12:51:16 PM (GMT Standard Time, UTC+00:00)