What's the Deal: Making Roads Bigger Actually Makes Traffic Worse

Induced demand is the term used by economists to describe how increasing the supply of something (such as roads) makes people want it even more. Though some traffic engineers noticed this phenomena as early as the 1960s, it wasn't until recently that social scientists gathered enough data to illustrate how it happens almost every time we create a new route.

I grew up in Los Angeles, the seaside city beside the freeway. And if there's one thing I've learned since I was old enough to sit up in my car seat, it's that traffic can happen at any time of day. Yes, rush hour is the worst, but I've driven on the 405 at 2 a.m. and encountered dead-stop bumper-to-bumper traffic.

I used to ask my parents why they couldn't just create extra lanes on the highway when I was a youngster. Maybe turn them all into double-decker freeways, with cars whizzing by on both floors. But, as it turns out, that's not going to work. Because if traffic engineers have learned anything in the last few decades, it's that you can't build your way out of a jam. Traffic is caused by the roads themselves.

Induced demand is the term used by economists to describe how increasing the supply of something (such as roads) makes people want it even more. Though some traffic engineers noticed this phenomena as early as the 1960s, it wasn't until recently that social scientists gathered enough data to illustrate how it happens almost every time we create a new route. These findings suggest that the standard methods for reducing traffic congestion are largely ineffective, and that if we could all simply be a little more logical, we'd all be spending a lot less time stuck in traffic.

But, before we get to the remedies, we need to examine the situation more closely. Two economists, Matthew Turner of the University of Toronto and Gilles Duranton of the University of Pennsylvania, decided to compare the amount of new roads and highways built in different U.S. cities between 1980 and 2000 with the total number of miles driven in those cities during the same period in 2009.

"We discovered this ideal one-to-one relationship," Turner added.

Between 1980 and 1990, if a city improved its road capacity by 10%, the amount of driving in that city grew by 10%. If the number of roadways in a certain city increased by 11% between 1990 and 2000, the total number of miles driven increased by 11%. It's as if the two figures were moving in unison, altering at the same precise rate.

Now, correlation does not necessarily imply causality. Perhaps traffic experts in American cities have figured out exactly how many roads to build to meet demand. However, Turner and Duranton believe this is implausible. The contemporary interstate system mostly matches the federal government's 1947 design, and it seems amazingly coincidental that road architects at the time could successfully estimate driving demand more than half a century in the future.

According to Turner and Duranton, a more likely explanation is what they call the fundamental law of road congestion: additional roadways will attract new drivers, resulting in the same level of traffic congestion.

Intuitively, I believe that expanding a road network is similar to replacing a tiny pipe with a larger one, allowing water (or cars) to flow more freely. Instead, it appears that the larger pipe is sucking in more water. The first question that comes to mind is where all these extra drivers are coming from. I mean, do they just appear out of nowhere as engineers construct new roads?

The solution relates to what roads enable people to do: travel around. Humans, it turns out, enjoy moving about. People will travel more if their ability to travel is increased, as they will be forced to drive into town if they live further away from where they work. Making driving easy encourages people to take more road trips than they would otherwise. Finally, companies that rely on roads will swoop into cities with a large number of them, bringing truckers and shipping with them. The difficulty is that all of these factors combine to degrade any extra capacity you've added into your street network, resulting in relatively constant traffic levels. People have an almost limitless urge to use roads as long as driving is simple and inexpensive.

You might imagine that putting more money into public transportation will help to solve the problem. Many railway and bus projects are promoted on this premise, with politicians guaranteeing that as passengers grows, traffic will reduce. However, the statistics revealed that even in cities that increased public transportation, traffic congestion remained unchanged. Some drivers will convert to public transportation if a new subway line is added. However, fresh drivers will take their place. It has the same impact as adding a new lane to a highway: traffic stays the same. (This isn't to suggest that public transportation isn't useful; it allows more people to get about.) According to Turner and Duranton, these initiatives should not be marketed as traffic relievers.)

Surprisingly, the impact also operates in reverse. When a city considers removing lanes from a road, locals shout that it will result in a massive traffic jam. However, the data indicates that nothing absolutely dreadful occurs. The volume of traffic on the route merely adapts, and the total level of congestion does not rise.

For example, in recent decades, Paris has maintained a consistent strategy of drastically shrinking and reducing roadways. "Driving in Paris used to be a nightmare," Duranton added. "It's not much worse, but it's just as horrible."

A freeway interchange in Los Angeles.

A freeway interchange in Los Angeles.

USGS
So, what happened to the other drivers? Many of them turned to public transportation, which has grown by 20% in Paris during the last two decades. Other trips were either avoided or completed on foot. Europeans aren't the only ones who want to get out of their cars. In 1989, San Francisco decommissioned the Central Freeway, which handled roughly 100,000 cars every day. The boulevard that replaced it today carries just about 45,000 daily cars, but they are still moving. (Yes, I've been stuck in traffic on Octavia Boulevard, but you don't always get through.) Perhaps the most notable success story occurred in Seoul, South Korea, where the city demolished a highway that carried 168,000 cars per day and was deemed a key traffic route. Traffic did not worsen once cars were replaced with a river, parkland, and a few smaller roads, and many other factors, including pollution, improved.

There is, however, a limit to all of this. If you reduce a 10-lane motorway to a single lane, traffic may come to a halt. If you double the length of the same 10-lane highway to 100 lanes, you might never see another car (or your city). While Turner and Duranton claim to have discovered a fundamental rule, it isn't the same as Newton's universal law of gravity.

Turner explained, "We can only assert that this is a rule within the spectrum of facts we can detect."

So, what can be done in this situation? How can we alleviate traffic congestion in the real world? Turner compared the way we currently use highways to the Soviet Union's manner of distributing bread. Goods were distributed equally to everybody under the communist administration, with a central authority establishing the price for each commodity. Because that price was frequently significantly less than what people were prepared to pay for that commodity, comrades would line up around the block to purchase it.

The United States government is also in the business of giving people with something they desperately need: roads. Uncle Sam, like the old Soviets, is giving this stuff away for pennies on the dollar. Is it thus necessary to privatize all roads? Unless you live in some sort of libertarian utopia. Congestion pricing is what Turner and Duranton (and many others who want to see more reasonable transportation policy) urge.

When demand is high, this means rising the cost of driving on a road. Drivers would have to pay a fee to utilize the most crowded roadways during rush hour. A few people will be put off by the cost and say to themselves, "I don't need to make this trip right now; I'll go later." Your city's roads have a lot of capacity that isn't being utilised. Consider how vacant they are in the early afternoon, late evening, and at night. We could better utilize the road's capacity if we gave vehicles an extra incentive to avoid the most crowded hours. The higher cost of driving would make public transportation a more appealing choice, encouraging more people to use it.
Congestion pricing has proven to be effective in cities like as London, Stockholm, and Singapore. Other cities are beginning to consider it as a viable option. In 2008, New York legislators rejected a plan for congestion pricing in the city, while San Francisco has flirted with the idea in the past. What is the issue? Voters. Even if it is in their best interests, no one wants to pay for something that was previously free.

If congestion pricing isn't an option, Duranton believes a more rational approach to parking could be a smart next step in reducing congestion. In most places, parking is significantly less expensive than it should be, and it is far too frequently free.

"Because it's free, people will abuse it, and it'll always be full," Duranton said. Drivers looking for parking are a major contributor to traffic congestion. "Some estimates claim that up to 30% of driving in the center portion of cities is people just cruising around for parking," Duranton remarked.

When demand for a parking area is high, raising the price will encourage individuals to depart sooner, allowing more people to park in the same spot during the day. Starting in 2011, San Francisco did just that, and the results have been a windfall to businesses because more customers can park in front of their stores. The initiative has actually saved motorists money since prices drop when demand is low. The city undertook a recent parking census in an effort to spread the meters outside of downtown and a few other districts, and discovered that it had more than 440,000 public parking spots, which would stretch longer than California's entire coastline if lined up end to end. Try bringing up that interesting information at your next cocktail gathering with city planners and traffic engineers.

Remember that the reason you're stopped in traffic isn't because of all the jerks who don't know how to drive around you; it's because of the road you're all on.
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