Concrete curbs or combined curbs and gutters serve several important functions.
Curbs collect water from crowned pavements and convey it to points of collection, thus reducing the amount of water that gets under the pavement.
They outline the edges of pavements and provide easily definable borders between traveled and untraveled surfaces.
They confine pavement structures, especially if the pavements are composed of layers of materials that must be compacted in-place.
Curbs help contain low speed traffic within the edges of pavements.