There shall be adequate provision for ingress and egress to all parking spaces. Where a lot does not abut on a public or private alley or easement of access, there shall be provided an access drive not less than eight feet in width in the case of a dwelling, and not less than eighteen feet in width in all other cases, leading to the parking or storage areas or loading or unloading spaces required hereunder in such manner as to secure the most appropriate development of the property in question, but, except where provided in connection with a use permitted in an R District such easement of access or access drive shall not be located in any R District.