You mention Costco as an example and claim that the return is (on average?) 30 feet away from your vehicle? Did you mean meters? Either way quite an underestimation. At our local meglo market (owned by Kroger) there isn't a return for every parking aisle. The distance and exposure to traffic to use a return is quite variable and can be significant. My local store is large enough that they have a cart returner as a dedicated position.