I suppose this subthread is complete, because you have now completely agreed with my original statement: you'll have to leave earlier for your trip to visit your friend, and delivery trucks will have to allocate more time (routes, trucks, drivers, etc.) for their deliveries. Alternatively, freight trucks might make fewer mostly-empty trips. Note that these two examples clearly match the characterization I provided: both may be accomplished at lower speed, with sufficient planning. This will be the "cost" of safe driving.