The traditional approach to roadway network planning has been to undertake a travel demand model analysis, identify the links that are predicted to experience congestion, and widen them to increase their capacity. While this may improve the operation of the section of road that is being widened, the release of that bottleneck frequently attracts more traffic to the area. As a consequence, other parts of the corridor or connecting roads, which may otherwise be expected to operate well, may become congested themselves.
Where roadway improvements lead to an increase in network efficiency, drivers may simply choose to commute further instead of banking the travel time savings. This effect actually increases the overall demand on the network in terms of vehicle kilometres travelled, which may negate some or all of the benefits achieved from the roadway improvements.
Efficient use of the limited funds available for roadway improvements means encouraging more efficient use of the network itself. The majority of vehicles on the road have only one occupant, and each driver requires much more road space than they would if they were sitting on a bus or riding a bike. Transit and active transportation also have wider benefits in creating more livable, healthier and more sustainable communities. When deciding which sections of roadway to improve, potential enhancements for these non-auto modes should be considered.
It is also important to remember that roads are conduits for the transfer of freight. Congested or otherwise inadequate goods movement corridors increase the overheads incurred in bringing products to stores and supermarkets, and this is often reflected in higher prices for the consumer. The direct cost of roadway improvements, in both financial and environmental terms, should be considered, too.