Because North Carolina is widening the southern stretch of I-40 that runs to Cary, we wondered: will adding more lanes reduce traffic?
This is important because the population of the Raleigh-Durham-Cary area is expected to double in the next 10 years. Many people say that the only way to handle that traffic is to add more lanes to our highways.
WIRED magazine wrote the best article on this
If you Google “does adding more lanes reduce traffic,” many of the articles that pop up reference a 2009 University of Toronto study by Gilles Duranton and Matthew Turner.
A piece by WIRED magazine is the only article that goes beyond repeating what Duranton and Turner found, and contributes some reporting of its own.
The reason the Toronto study is so widely cited is that it found that adding more lanes increased the amount of miles driven by local residents. In other words, rather than easing traffic congestion, adding more lanes only induces people to drive even more.
People see a wider freeway and think of all the places they can go. Businesses see a new method of attracting customers who used to be far away. Governments see a new multi-million road expansion needs to be paid for.
If adding lanes is bad, is reducing lanes good?
In 1989, San Francisco replaced its Central Freeway, which carried 100,000 cars per day, with a smaller boulevard that could only handle 45,000 cars per day. Instead of doubling the congestion, the new boulevard hums along with normal amounts of traffic.
People found other routes to take. Traffic was distributed across other sources, and the city didn’t have to take on a years-long expansion project. Pollution also declined because cars kept moving on other roads instead of sitting idle on the Central Freeway.
Iowa is another good example
Iowa is in the same boat as Raleigh as it thinks about expanding I-380 between Cedar Rapids and Iowa City to accommodate commuters.
An increasing population and lack of bus or train options has city planners looking at ways to reduce traffic for people shuttling back and forth across the main highway.
A book called, “Traffic: Why We Drive the Way We Do” is stressing many points to Iowans similar to the WIRED magazine piece. Bigger roads will mean more drivers, which will mean more traffic. Local budgets will be responsible for maintaining more miles of road, and ultimately taxpayers—whether they commute or not—will be expected to pay the increased cost of maintenance.
Bigger roads also induce people to drive faster and take more chances since the increase in space gives the illusion of more time to react. In reality, the slower speeds of smaller roads keep people from driving recklessly and therefore reduce collision rates. It’s a classic example of our eyes tricking our brains.
What’s the solution?
The data indicate that smaller roads are better for traffic, not bigger ones. It’s counterintuitive and will take some getting used to, but it’s better to make decisions based on data instead of the gut.
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