Most likely, it won't work, and will come at a heavy cost, both direct and indirect.
In transportation-planning speak, the reason road widenings rarely alleviate traffic congestion comes down to two words: induced demand. Think of traffic less like a constant flow of vehicles, and more like a gas which expands to fill its container. If you create more road space, it "induces demand" for more driving. Some people will drive who otherwise would have skipped the trip or taken a different route. Some will drive at rush hour who otherwise would have chosen a less-busy time of day. Over time, more homes and businesses will locate farther apart from each other, to take advantage of the increased road capacity. Congestion will soon return to previous levels.
Want evidence to further understand this phenomenon or to help you convince others?
- Here's a Strong Towns article about why road widening doesn't work (and the converse: removing or narrowing roads does work) with case studies from four cities: Houston, Dallas, Louisville, and Rochester.
- Here's another Strong Towns article on why urban freeway expansion is futile, with more of an engineering bent.
- In 2016, we profiled and shared a study by the Frontier Group on the high costs of highway boondoggles.
- Our friends at City Observatory did an in-depth look at Houston's Katy Freeway, one of the widest in the world, which was expanded to 23 lanes at a cost of $2.8 billion. In the three years following the project, PM rush hour travel times actually increased by over 50%.
- An academic study in 2009 demonstrated the induced demand effect for urban freeways.
Large infrastructure projects like highway widenings are often accompanied by studies that purport to show great economic benefit. These studies are in fact misleading and pseudoscientific, and show vastly inflated, illusory benefits. These links explain why.
The downsides of widening a highway are many: a wider road means increased pollution, a more formidable barrier between neighborhoods, and of course the direct expense of maintaining and eventually replacing the roadway.
