Figure 10-4 illustrates a typical grate inlet. Water falls into the inlet through a grate instead of an opening in the curb. Designers use many variations of this inlet type, and the format of the grate itself varies widely as each foundry may have its own series of standard fabrication molds.

For the most part, grate inlets are used in sag configurations in gutters, adjacent to concrete traffic barriers or rails (where curb inlets would not be practicable), V-shaped gutters with no curb or barrier, and ditches. Grate inlets may also be used at on-grade situations combined with curb inlets.

Grate inlets adapt to urban roadway features such as driveways, street intersections, and medians. When grate inlets are specified, the grate configuration and orientation should be compatible with bicycle and wheelchair safety.

Access to the storm drain system through a grate inlet is excellent in that, usually, the grate is removable. On the other hand, maintenance of grate inlets can be a continuing problem during the life of the facility; the propensity to collect debris makes grate inlets a constant object of maintenance attention. As such debris accumulates it obstructs the flow of surface water into the inlet. Grate inlets also present potential interference with bicycles and wheelchairs.