Means the clear average width of the existing carriage way and footpaths only on which the building or plot line abuts. The average width shall be computed by taking length of street between two extreme points on building unit abutting the street at right angles to the direction of such streets excluding the steps projections, forecourts, open areas of other spaces in front of the building erected or intended to be erected. However in case where a regular line of street is prescribed by the Competent Authority, such width shall be considered for the purpose of computing building height.