‘Induced Demand’

The common wisdom when faced with traffic congestion seems to be that just adding more lanes will sort everything. It won’t.

Whilst it may initially relieve some pressure, it won’t be long before more traffic arrives to fill the space.

Just as with the Katy Freeway expansion, adding new roadway capacity also creates new demand for those lanes or roads, maintaining a similar rate of congestion, if not worsening it. Economists call this phenomenon induced demand: When you provide more of something, or provide it for a cheaper price, people are more likely to use it. Rather than thinking of traffic as a liquid, which requires a certain volume of space to pass through at a given rate, induced demand demonstrates that traffic is more like a gas, expanding to fill up all the space it is allowed.

via Traffic Jam? Blame ‘Induced Demand.’ – CityLab

Before thinking that more roads; bigger roads; wider roads; faster roads is the answer to our problems, we should look to America. The land of the 22-lane motorways. The i10 in Florida for example, has an average of 22 lanes, occasionally increasing to 26 in places, yet it still gets clogged up at rush hour.

If you make motoring easier, more people will choose motoring. As they put it:

Initially, faster travel times (or the perception of faster travel times) encourage behavioral changes among drivers. An individual may choose to take the new highway to a more distant grocery store that has cheaper prices. Trips that may have been accomplished by bike or public transportation might now be more attractive by car.

Sadly, the cost of building more roads is rarely just financial. It’s in the habitats and communities that are bulldozed to make way where the long-term effects are felt.

Fortunately, this phenomena isn’t confined solely to car traffic. By installing cycle lanes in London, Manhattan and numerous other places around the world, people started to cycle. Combined with the congestion charge, London’s traffic has shifted.

He added: “The new protected cycle lanes that opened last year in London can move five times as many people per hour as a main carriageway lane in the most congested parts of our city. At peak times, the new cycling infrastructure moves an average of 46% of people along the route despite occupying only 30% of the equivalent road space.

“Just two weeks after opening, the east-west and north-south cycle superhighway roads were moving 5% more people per hour than they could without cycle lanes – and that number is increasing as more cyclists are attracted to the routes.

via London’s cycle lanes ease congestion, rather than cause it as cycling keeps growing in capital | road.cc

Cities need to decide what sort of traffic they want, then plan and build for it. Prioritising more efficient modes of travel to the detriment of more inefficient modes can change a city for the better.

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