Traffic Is Water, and Other Bad Assumptions in Transportation Planning

Here’s a question for you to consider: if a road is congested, should it be widened? If you answered yes, can you name a major urban highway widening project that didn’t revert within five years to the same average traffic speed as before the expansion?

Widening a road to alleviate congestion is an intuitively obvious solution to most Americans.  Generations of planners reinforced this thinking when they told Americans that traffic is like water: if you have too much flowing in a channel, you need to widen it. 

You can see this attitude in play all over the US. Whenever a road gets busy, planners and commuters look for ways to widen it, no matter what the effect may be on communities abutting the road. Arlington, Virginia homeowners along Interstate 66 near Washington are constantly under threat of a major widening because commuters further out think a wider road will speed up their drive times.

Too bad it wouldn’t work. Atlanta widened the Downtown Connector (I-75/85 from just north of downtown to just north of Atlanta Airport) from six lanes to twelve lanes in the 1980s. HOV lanes were added in the 1990s. Guess how much faster traffic goes today versus the 1980s? If you answered “no faster”, pat yourself on the back and send your resume to your nearest DOT. 

The ever-expanding Downtown Connector in Atlanta, GA. Look, in the distance you can see it growing AGAIN! Photo courtesy of Connor Carey/Wikipedia.

Need another example? Try this: a project infamous for its $15 billion cost is The Big Dig, or Central Artery Project, in Boston. The Big Dig’s main source of fame is the removal of an ugly elevated highway that divided the city, but it’s also supposed to provide some congestion relief. However, the Boston Globe reports that commutes are actually worse than ever with travel times actually doubling several years after completion. Removing one traffic bottleneck, as in this case, does no good for the bottlenecks that remain and may exacerbate the problem by tempting more drivers onto the roads. 

One of the tunnels built for the Big Dig in Boston, MA. Photo courtesy of Rene Schwietzke/Wikipedia

This demonstrates the basic fallacy with the traffic-as-water theory: water is not a rational actor. Water can’t be tempted. Likewise, if water’s flow is too great, it can’t opt to move its source closer to its destination. Nor, for that matter, can it move its destination closer to its source. 

Human beings do this all the time. That’s why home prices in close-in, walkable neighborhoods around large urban centers throughout the US held steady or increased in recent years, while prices in far-flung neighborhoods melted down faster than a Japanese nuclear power plant. 

In the Washington, DC area, home foreclosures in the suburbs form what some real estate experts describe as a “ring of fire”. The center is nice and cool---at least, the fires of foreclosure don’t rage there. But in the outer counties such as Loudoun in northern Virginia, empty McMansions abound. Derelict subdivisions are seldom viewed by young buyers as great places to bring up families. 

The inner suburbs and downtown areas were already enjoying resurgence thanks to their vastly shorter commute times, so their vibrancy was a natural lure to these new homeowners. Why live in a depressed area a long drive from work when you can live in a fun place that allows you a multitude of commuting options?

So, the debate is settled: there’s no more need to expand transportation options to the suburbs because they are emptying out, right? Well, not everyone agrees with that assessment. Kenneth Johnson, senior demographer at the Carsey Institute at the University of New Hampshire, thinks that the migration into the cities could reverse once the economy recovers. The flight to the suburbs that outweighed central city growth in every decade since the 1920s would restart once mortgages became obtainable.

As a result, some planners think we should expend resources expanding suburban commuter options just as we did in the past, even if the assumptions behind that decision appear uncertain. But is it smart to spend billions of dollars on a scenario that, while once was almost a certainty, seems to be fading into history?

If we look to other developed nations, such as those in the European Union or Japan, where do we see the most expensive real estate? Inevitably, it’s in the urban core where transport links are the most robust. The low-income residential areas are located on the distant periphery. 

Perhaps that’s the hidden story here: America’s urban development isn’t taking a pause from its normal pattern of urban rot and suburban boom. It’s resetting to what is the normal global pattern: popular cores with declining demand further out. If so, America’s planning meme is in need of a reboot, or else a lot of money will be wasted.