(1) Where a sign prohibits parking the operator of a passenger vehicle may nevertheless stop on the right side of any two-way street, or either side of any one-way street, for the purpose of loading or unloading passengers, and further, such a sign shall not prohibit the operator of a commercial vehicle from loading or unloading.

(2) Operators of commercial vehicles shall be permitted an additional period of 20 minutes after loading or unloading to transact business incidental to such loading or unloading.

(3) The operator of a passenger vehicle may stop temporarily in a curb loading zone for the purpose of the expeditious loading or unloading of passengers when such stopping does not interfere with any commercial vehicle about to enter such zone.