I can only give you my opinion: the Start/Stop feature is exactly for this type of usage. Gas mileage is lowest when stop/starting a great deal- the S/S feature assists the owner of the vehicle to counteract poor gas mileage.
2013 BMW X3 28i - Deep Sea Blue Metallic, Sand Beige Nevada Leather, Fineline Sienna Wood Trim, High-Gloss Roof Rails, and BMW Apps. Goodyear Eagle LS 2 All Season Tires.
Packages: Cold Weather, Convenience, Dynamic Handling, M Sport, Premium, Premium Sound with XM Sirius, and Technology.