Curb Opening Inlets
Figure 10‑2 illustrates a generic example of a typical curb opening inlet. Curb inlets are used in urban sections of roadway along the curb line.
Figure 10-5. Curb Opening Inlet
Most curb opening inlets depend heavily upon an adjacent depression in the gutter for effective flow interception (see
). Greater interception rates result in shorter (and probably, more economical) inlet lengths. However, a large gutter depression can be unsafe for traffic flow and bicycle operation near the gutter line. Therefore, a compromise is in order when selecting an appropriate value for the gutter depression. The depth of the gutter depression should be:
- 0 to 1 in. (0 to 25 mm) where the gutter is within the traffic lane
- 1 to 3 in. (25 to 75 mm) where the gutter is outside the traffic lane or in the parking lane
- 1 to 5 in. (25 to 125 mm) for lightly traveled city streets that are not on a highway route.
Figure 10-6. Curb Opening Inlet Depression
Some municipalities in the state prefer to recess curb inlets with significant depression to minimize interference with traffic flow. The inlet is recessed from the line of the curb and gutter such that the depression does not extend beyond the gutter line. This may improve driveability; however, the curb transition may pose a hazard to traffic.
Curb opening inlets are useful in sag and on-grade situations because of their self-cleansing abilities and hydraulic efficiency. Additionally, they are often preferred over grate inlets because the inlet is placed outside the travel way and poses less of a risk to motorists and bicycle traffic.
A drawback of curb opening inlets is that the flowline of the opening is fixed and not readily adaptable to changing pavement levels as occur in surface treatment overlays. Successive overlays can gradually reduce or even eliminate the original opening available for water removal, unless the pavement edge is tapered to the original gutter line.