"The evidence also showed that sewer grates are an integral part of the sewer system. The direction the bars of the grate run (whether parallel or perpendicular to the curb) is determined on the basis of hydraulic efficiency. At a low point in a street, water has no velocity, so the direction of the bars is of no consequence. However, when water is moving downhill and thus has velocity, a parallel configuration is necessary in order to remove the water from the street. If the bars on a grate located on a downhill slope are perpendicular to the curb, the water jumps across the grate rather than into it. Therefore, while a perpendicular configuration would be bicycle safe, it would be hydraulically inefficient.
[Further analysis on hydraulic efficiency from John Forester: "This is not particularly relevant. It is correct that at grate with old-fashioned bars across the direction of flow will drop only about 70% of the water flow into the sewer below, leaving the 30% of jump over and continue down to the next grate. However, that grate, having greater flow over it, will intercept more water than it would have if all the water above had been intercepted by the higher grate. Assuming that the grates are equally spaced, and the water to be caught falls equally on each length of the roadway, we have the following for the amounts falling and the amounts dumped into the sewer by the sequence of grates, given as proportions of the theoretical equal flow. 0.7, 0.91, 0.97. In short, in a sequence of three grates, the amount being caught by each grate has become indistinguishable from the case in which the grates have 100% efficiency. As the court notes, once the grade levels out, the grates on the level catche all the water, so that these grates do not affect the result.
"In short, the argument about the lower hydraulic efficiency of cross-bar grates is erroneous in the general case, and has effect only when the slope is so short as to have only 1 grate on it, in which case the bottom grate will take care of the problem.
"Also, the newer grate designs, besides being bicycle safe, are also hydraulically efficient, because the bars are cast at the angle to catch the water."]
[...]
"In response to plaintiff's allegations of negligence, the City argues that it is immune from liability under the facts in this case. ...
[...]
"In the present case, the sewer grate was a part of the general drainage and sewerage system of the City of Atlanta and was constructed according to the City's general engineering plans as they existed many years before plaintiff's accident. However, in recent years sewer grates such as the one in question have become unsafe for bicycle traffic due to changes in the width of the tires on many models of bicycles. Since 1972 the City has been purchasing sewer grates which are bicycle safe. These grates are installed on all new construction projects and are also used to replace existing grates which are no longer functional or about which complaints have been received or replacement requested. However, the City has determined that it is not economically feasible for it to replace all existing sewer grates with new bicycle-safe grates. ...
"The facts disclose that the City was generally aware that sewer grates which have bars parallel to the curb pose a potentially dangerous obstruction to some bicyclists using city streets. Nevertheless, whether the grate in question constituted a dangerous obstruction to persons using the street in an ordinary manner, as plaintiff was, and whether the City exercised ordinary care to remove the alleged obstruction or to put barriers or warnings near it, are questions of fact which must be resolved by a jury. ... Accordingly, the trial court erred in granting the City's motion for summary judgment.
[Click here to continue reading.]
Disclaimer