The accumulation of debris at the curb is caused by the design of the street and vehicular movement. Streets are designed with a crown in the middle sloping toward the sides. Water and debris move toward the curb and gutter areas. Vehicle movement scatters debris to the edges of traffic lanes. Streets with no curbs are affected by the same factors as curbed streets, but with no curb the debris is dispersed onto areas adjacent to the paved surfaces.
Uncurbed streets are, in effect, self-cleaning.
The policy recommendation of the study was that no residential or arterial blockface be swept with a street sweeper unless a minimum of 75 percent of its length is curbed.