It is important to consider drainage needs along bicycle and pedestrian routes to ensure flooding or water ponding does not occur and inhibit these travel modes. Curb and gutter is one of the primary tools used to capture water runoff from a roadway and divert it to properly placed inlets or catch basins – it is also one of the primary dividing lines between pedestrian zones and vehicle zones within roadway right of way. Bicyclists typically ride near the curb and gutter section of a roadway, or as far right as practicable. Therefore, it is particularly important to ensure that inlets, catch basins, and grates not only adequately allow water to drain, but also allow for the safe passage of bicyclists and pedestrians.
Part 1 of the NCDOT Roadway Design Manual discusses Drainage Design in Chapter 5. Below are excerpts that indicate the standards to use for circumstances.
Pedestrian Considerations
For pedestrians, it is important to ensure that grates do not interfere with providing an accessible route. They should be stable, firm and slip resistant, and spaces in the grates must be no wider than ½ an inch. Elongated openings or slotted grates must be placed “perpendicular to the dominant direction of travel,” per 4.5.4 of the ADA Accessibility Guidelines for Buildings and Facilities (ADAAG). This ensures that the grates are not tripping hazards, and that wheelchairs with small caster wheels or individuals using canes, walkers or crutches do not get caught in the grate slots.
Bicycle Considerations
For bicyclists, it is particularly important that grate slots be perpendicular to the travel path so that bicycle wheels cannot get caught. However, it is also important to ensure that the inlet allows for typical amounts of debris to drop through without clogging the inlet – this debris would not only impede the draining function of the inlet for future water runoff, but it could also become another obstacle for bicyclists to avoid.