Here in Cardiff we are a few weeks away from seeing the removal of tolls on the Severn Bridge, potentially adding to the traffic woes experienced around Newport.
However, the common wisdom seems to be that just adding more lanes, or a relief road will sort everything. It won’t.
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.
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.