Section 54(1)(b) in West Bengal Municipal (Building) Rules, 2007
(b)The minimum width of such internal roads shall be 3.50 metres. Where internal road of 3.50 metres in width is not possible to be provided due to an existing building constructed prior to the enforcement of these rules, a building of not more than 7.0 metres in height may be allowed, provided that the width of the internal road shall not be less than 1.20 metres.