Traffic

The "less space equals more traffic" theory, known as level of service, was once the established rule of traffic engineering, but it has long been discredited. To show how traffic really works, we need to look at a different supply and demand concept, called induced demand, which simply means the more you increase the supply of something, in this instance roads, the more people use it. This is because when you expand a road, travelling by car becomes quicker and easier in the short term. And this makes travelling by car more attractive, and so more people are more likely to use their cars than usual. More car trips equals more cars on the road, and all that extra space quickly disappears. Now there is a limit to all of this. If you make a 10-lane motorway into 100 lanes, you could travel without seeing another car for miles. But we're not talking about a mathematical principal, we're talking about human behavior, which is often influenced by a whole host of different factors. Something which the level of service argument cannot account for. So what impact does the introduction of new bike lanes have? Well the induced demand effect also works in reverse, which means when you reduce road capacity, by introducing new bike lanes for instance, again there is an immediate impact, but this time car travel becomes slower and more congested in the short term. This then discourages road use and as a result congestion will largely go back to similar levels as it was before and in some cases go down. It's called traffic evaporation.