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
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
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
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.
- Neenah Foundry Catalog, from Neenah
Foundry Company, PO Box 729, Neenah WI 54956, 1995
- "The Grates of Cincinnati;" Don Burrell; Bicycle
Forum #13, Fall 1986
- Manual on Uniform Traffic Control Devices; FHWA; 1979
Topics for further study:
- Grates that are either higher or lower than the roadway surface
- Grate location within the roadway
- Slippery grate surfaces
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