The city's transportation department has noticed that the city's extensive public bus system generally runs behind schedule on days when traffic is heavier in the city. The transportation commissioner concluded that the traffic prevents the buses from reaching their stops on time, despite the existence of a number of bus-only lanes throughout the city. He has therefore proposed creating additional bus-only lanes on city streets to allow more buses to bypass traffic.
The success of the commissioner's proposal depends on which of the following assumptions?