Transport planners have an instinctive tendency to assume that since traffic growth has accompanied economic growth in the past, it follows that supporting economic growth requires more road capacity to support future traffic growth. However, it is a fact that the rate of traffic growth in most countries exceeds the rate of economic growth, suggesting that something else is causing the change in travel patterns.
Curiously, we don't bother to ask ourselves why traffic is growing faster than the economy, and whether the economy would suffer if we didn't build roads to accommodate the historic rate of traffic growth. In fact, in many cities, road capacity has not expanded at the same rate as traffic has grown, and yet the economy is growing well. South Africa's three biggest cities are a case in point.
Isn't it possible that the increase in traffic is not so much a result of economic growth, but a consequence of having enough available capacity for more people to drive at the same time? In many cases delays from congestion are increasing, so there could be other reasons, such as changes in the nature of the economy, or more families with two cars, or changed urban spatial patterns, or inadequate public transport. I don't claim to know the reasons - my concern is that decisions to spend billions to add road capacity are based on a limited assessment of what is really needed for the transport system (and the economy) as a whole.
Social commentator Jane Jacobs posed the question in Dark Age Ahead: if building more roads results in more traffic, isn't it logical that building fewer roads would result in less? WorldChanging reports on how shutting down lanes of Interstate 5 through Seattle has not brought traffic to a standstill. This is an unintentional experiment in using congestion to manage traffic. Usually, the problem with congesion is that it is unpredictable, often the result of traffic accidents or other unplanned incidents, so drivers don't have forewarning or access to information to enable them to make alternative arrangements. But in this case, all the hype beforehand gave people an opportunity to change - and it seems that this is exactly what they did.
The issue is an important one for sustainability. The general approach to transport planning is based on, and reinforces, the dominant trends in travel patterns. If historic trends are not necessarily critical to economic and social wellbeing, then we should take a good look at why they are being supported. It is quite possible that money could be more effectively spent elsewhere to improve alternative modes of travel and reduce the negative impacts of road traffic.
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