Smart Traffic Congestion Reductions

Conventional transport planning tends to assume that any increase in per capita motor vehicle travel is desirable, economic theory recognises that too much vehicle travel is as harmful as too little since vehicle travel and the facilities they require are costly. Figure ‘Optimal Vehicle Travel and Road Supply’ illustrates this concept. As a transport system increasingly becomes totally car-free (no automobiles at all) it leads to significant benefits, but beyond an optimal point, benefits decline and become negative.

As a result, developing countries benefit from planning practices that support transport system diversity, efficient pricing, and accessible land use development. Although many developing countries can justify roadway improvements to accommodate growing traffic volumes, these should consist of paving local roads and building intercity highways. It is ineffective and inefficient to try to reduce urban traffic congestion by expanding unpriced roads. Developing countries will be better off by implementing a combination of improvements to alternative modes and pricing reforms.

Course of action

Conventional transport planning tends to consider traffic congestion a major cost and congestion reduction a primary planning objective. It often evaluates transport system performance based largely on congestion indicators such as roadway Level Of Service and the Travel Time Index. This tends to justify congestion reduction over other planning objectives and roadway expansion over other congestion reduction strategies.

But congestion cost and congestion reduction benefit estimates are sensitive to the evaluation methods used. Current planning practices tend to exaggerate congestion costs and roadway expansion benefits in various ways. More comprehensive and objective analysis indicates that traffic congestion is actually a moderate transport cost overall, and roadway expansion is generally less effective and beneficial than other congestion reduction strategies.

Chronic traffic congestion can be considered a symptom of more fundamental transport system problems such as inadequate mobility options that force people to drive for every trip, and dispersed land use patterns that increase travel distances. Failing to efficiently price road use is a market distortion that results in economically excessive motor vehicle travel. Roadway expansion under such circumstances tends to do little to reduce long term congestion and increases other transport problems.

Excessive estimates of congestion costs and congestion reduction benefits tend to contradict transport equity objectives: They favour motorists over non-motorists and reduce the quality of transport options available to people who are physically, economically and socially disadvantaged. Congestion reduction strategies can be designed to support transport equity objectives by improving affordable modes, progressive pricing, and more affordable housing in accessible, multi-modal locations.

Comprehensive congestion analysis is particularly important in developing countries where vehicle travel is growing rapidly. Although many countries are at a point in their development in which travel demand is growing and roadway improvements are cost effective, it is important that they use comprehensive analysis when evaluating congestion reduction options. In most cases, a combination of alternative mode improvements, pricing reforms and smart growth policies will be more cost effective, beneficial and equitable than expanding unpriced urban roadways.

This is not to suggest that driving is bad or that highways should never be improved. However, when all impacts and options are considered, highway expansion is significantly more costly than advocates claim and provides less overall benefit than many alternative policies and programmes. It is important that decision makers and the general public understand the omissions and biases.

(Todd Litman has worked on numerous studies that evaluate transportation costs and innovations. He has worked as a research and planning consultant in more than two dozen countries.)