The Recumbent Blog got its hands on the installation instructions for continuous milled rumble strips in Alberta, Canada. It’s worth looking at in the context of our discussion of rumble strips to examine what’s good about the approach and what could be improved.
In our report on rumble strips, we highlight four common problems with rumble strips that should be addressed in bicycle-tolerable installation: 1. strips that are too wide, 2. grooves that are too deep, 3. strips not placed near the fog line, and 4. strips that are continuous.
Let’s take the width first. Some of the most bicycle-tolerable designs call for 5 inch wide rumble strips, but strips are sometimes 16 or 18 inches wide and even occasionally take up the entire shoulder (see the photo in our previous post). In that context, the one foot wide strip here could be a lot worse.
Second, relatively speaking, 8 mm is a very favorable rumble strip depth for cyclists.
The third issue is placement. Strips should be placed within a foot of the fog line, and the Alberta installation calls for this, which is great. So far the guidance is three for three. The trick with placement is that sometimes implementation doesn’t follow the plan. Sometimes the agency doesn’t even know that the contractors are mis-installing the strips until bicyclists bring it to their attention, so advocates should monitor rumble strip installation to make sure the strips are installed correctly.
In the photo below from the Recumbent Blog, you can see the strip sitting snuggly against the white fog line. The best part of the example below, though, is the six foot remaining ridable shoulder to the right of the strip. Guidance from the US Federal Highway Administration (FHWA) says that strips should not be installed unless there is at least four feet remaining (five if there is a guardrail). Six feet makes this a comfortable ride — and gives drivers plenty of time to correct their trajectory before their fully off the road.
The fourth potential issue is the only one that I’d suggest they re-visit. These strips are continuous. They do not include any gaps to allow cyclists to cross into the travel lane to avoid debris or rough pavement.
I’d like to thank the Recumbent Blog for bringing up this real life example that gets close to following bicycle-tolerable practices. What we tell state and local advocates is that rumble strips are not going anywhere. FHWA and state DOTs see them as an effective and inexpensive safety tool. The trick for bicycling advocates is to urge agencies not to install rumble strips indiscriminately (i.e. only when conditions call for it and there are sufficient shoulders,) and to follow bicycle-tolerable practices when they do install them.
League Policy Director
Flusche joined the League in April 2009 and has a B.A. in history from Syracuse University and a Masters of Public Administration with a concentration in public policy analysis from New York University.