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Making a road concave increases its water capture and drainage capacity. Combined with a pavement (sidewalk) and a slightly raised floor level in the homes built alongside it, this can prevent flooding in the homes.
Hollow roads or sunken channels can hold and drain much more water than gutters. Slopes are often less of an obstacle for covering larger distances than for a fluted gutter of which the maximum length is 50 metres, because the distance to buildings is often greater, and therefore the channel level can be varied. But bikes, cars, etc. also use these channels when it rains; this can be a nuisance due to splashing water. For this and other reasons sunken channels are not applicable in all situations.