Image: thanks to Neenah Foundry, Neenah WI
copyright 1996, Tracy-Williams Consulting

Replacing or modifying dangerous drain grates is one of the most basic improvements a community can make for bicyclists. Fortunately, doing so is a relatively simple procedure.

What are drainage grates and why are they dangerous?

First, it's important to realize that a drainage grate, as part of a road's drainage system, is an important roadway feature. It allows storm water runoff that has flowed from the roadway into the gutter to be taken away via a subsurface system of pipes or to enter the groundwater through a sump.

For this reason, any changes made to a grate must take hydraulics into account. A "bicycle safe" grate must let water pass without allowing routine types and amounts of debris to clog the inlets--and without trapping bicycle wheels. And that, by the way, is the primary danger for bicyclists. Many traditional parallel-bar drain grates have slots wide enough to swallow some bicycle's wheels. A bicycle drops in, perhaps up to the fork, the wheel stops, and the rider catapults over the handlebars, landing in a heap in the gutter. Numerous agencies have been successfully sued for allowing such grates to go unaltered.

How do you fix dangerous grates?

The best approach is to replace them with "bicycle safe" grates like that shown above. This model is a "vane" design and is known for having good hydraulics and being very safe for bicycles.

There are many other designs that are also "bicycle-safe." Steel grates designed in a honeycomb pattern work well and are the standard for the State of California. Iron grates with a herringbone pattern of holes also are good and are standard for the State of North Carolina. Curb-face inlets take the water into a hole in the curb and have no slots on the road surface. While curb-face inlets offer an excellent solution, removing the grate entirely, they can, however, cause handling problems for bikes if the roadway slopes excessively toward the inlet.

Note: If an agency's current design standards call for dangerous grates on streets where bicycle traffic may be present, they should immediately replace the standard and set up a process for replacing the grates themselves. There is no excuse for perpetuating the mistakes of the past.

Alternatives to replacing dangerous grates include placing covers over the top and painting warning markings on the roadway to direct bicyclists away. The first option tends to be a temporary fix. Steel straps welded over the top of a grate can, over time, come loose. And sending a welder out into the field is a very expensive way to handle such problems.

As for striping, the Manual on Uniform Traffic Control Devices (MUTCD) gives advice on how to do this. However, it's not a good idea to rely on such a passive approach to warning bicyclists away from hazards. And paint wears off.

What are the benefits?

The primary benefits are a reduction in bicycling hazards, a lessened risk of injury for riders, and a resulting reduction in the potential liability for the agency responsible for the roads.


Topics for further study:

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