The Antiplanner’s Library: Traffic

The Antiplanner finally picked up a copy of Traffic: Why We Drive the Way We Do (and What It Says About Us), a popular book by journalist Tom Vanderbilt (whose web site, How We Drive, seems to be down at the moment). Vanderbilt interviewed numerous people (including several of the Antiplanner’s friends) to learn about the psychology and physics of driving.

Vanderbilt explains that the word “traffic” doesn’t mean “congestion” but simply “movement.” Appropriately, the book focuses at least as much on safety as on congestion. Vanderbilt is an entertaining writer who manages to present a balanced view of many controversial issues.

For example, one chapter is titled “Why More Roads Lead to More Traffic.” He explains that, in many urban areas, congestion has led to a “latent demand” for more travel: that is, people would drive more if the areas were less congested. So, when new roads are built, they soon fill up. That doesn’t mean that new roads would get congested if they were built in an area that didn’t suffer from so much congestion that there was a significant amount of latent demand.

“Latent demand is often described by another phrase, ‘induced travel,’ which is really just a twist on the same thing,” Vanderbilt adds. “There is a huge and enervating literature about this, which I heartily do not recommend” (pp. 154-155). The Antiplanner would add that induced travel is a spin term designed to make us think that such travel is frivolous or (even more irrationally) that new roads really do increase travel demand (just like new cell towers lead to more phone calls and new hotels lead to more adultery). But Vanderbilt, perhaps wisely, avoids this issue.

I have a few minor quibbles with Vanderbilt’s book; perhaps the biggest one has to do with congestion pricing. Vanderbilt makes the common mistake — one sometimes made even by advocates of congestion pricing — of suggesting that the goal of congestion pricing is to reduce auto driving. “Congestion pricing can help reverse a long-standing vicious cycle of traffic,” says Vanderbilt, “one that removes the incentives to take public transportation” (p. 167). In other words, congestion pricing can get more people to ride transit.

It sounds so elementary, but it’s worth a shot. cialis soft http://www.opacc.cv/documentos/listas/B%20O%20n%2013_II%20Serie_2014-Lista_Nacional_Contabilistas_Auditores_Certificados_AUTORIZADOS.pdf Individual results might vary depending upon a lot of other conditions also. view this link order viagra professional The studies showed the herb Eclipta cialis 5 mg in natural methods to prevent underweight problem appears to inhibit viral replications due to the presence of bioactive photochemical. They levitra professional followed the routine mentioned by the Righraj and she was finally pregnant. In fact, the real goal of congestion pricing is to increase traffic flows and allow more people, not less, to drive during rush hours. As Vanderbilt himself notes, when freeway speeds are 55 mph, a single lane can move as many as 2,400 cars per hour. But at 35 miles per hour, the same lane can move only 1,700 cars per hour (p. 121). If there are 2,000 cars per hour trying to get through the lane and one of the slows to 35, even for an instant, suddenly the lane’s capacity is below the demand and speeds will remain at or below 35 until the demand falls below the new capacity. (Traffic engineers call this “level of service F.”)

The purpose of congestion pricing is to make sure that volumes remain low enough that “incidents” (such as one car slowing down) do not cause capacities to fall below demand. A well-designed congestion pricing system can therefore maintain throughput at, say, 2,000 cars per hour instead of the much lower throughputs that would result if speeds fell to 20 or 30 mph. Potentially, then, congestion pricing can effectively double rush-hour highway capacities.

Maybe if we did a better job of explaining how congestion pricing will increase, not decrease, people’s mobility, there would be less opposition to the idea. Unfortunately, some people do want to use congestion pricing to reduce driving (not necessarily including Vanderbilt), which means they would charge much higher rates than needed to keep traffic flowing so that they can divert the funds to expensive rail transit projects.

Congestion pricing isn’t the only tool that can maintain traffic flows. Another is adaptive cruise control, available on on the top-of-the-line Prius as well as many more expensive cars. This technology combines lasers or radar to detect a car in front of your car with electronic acceleration and braking to keep your car a fixed distance from the car ahead.

Vanderbilt explains that a lot of congestion takes place because cars run in “platoons.” If the lead car in a platoon slows, all the cars behind it must slow a little more because of people’s slow reaction times. Eventually, if the platoon is long enough, one car and all the cars behind it grind to a halt, leading to a stop-and-go traffic situation even though no one who has to drive through it ever knows what caused the slowdown in the first place.

Adaptive cruise control can prevent this from happening. As Vanderbilt notes, simulations have found that if “as few as two in ten drivers” use adaptive cruise control, many traffic jams “could be avoided altogether” (Vanderbilt’s emphasis, p. 129). So one alternative to congestion pricing might be to accelerate the introduction of adaptive cruise control on more affordable cars.

Still, Vanderbilt’s book is less about solving congestion than helping people understand their personal driving habits. It is very good at doing so, but those who want a book that focuses on reducing congestion will have to look elsewhere.

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About The Antiplanner

The Antiplanner is a forester and economist with more than fifty years of experience critiquing government land-use and transportation plans.

3 Responses to The Antiplanner’s Library: Traffic

  1. the highwayman says:

    Congestion pricing doesn’t decrease peoples automobility, it just put’s a price on it.

    So with price signals, some people will change when they drive or change modes of traveling.

    Though there are groups against such things. http://www.notolls.org.uk/

  2. Mike says:

    THWM:

    1. Learn how to use the apostrophe.

    2. Yeah, essentially. Heck, I wouldn’t take transit if it weren’t a cheaper option than driving. It sure does take longer, so something has to balance out that shortcoming.

  3. Francis King says:

    Antiplanner wrote:

    “he Antiplanner would add that induced travel is a spin term designed to make us think that such travel is frivolous or (even more irrationally) that new roads really do increase travel demand (just like new cell towers lead to more phone calls and new hotels lead to more adultery).”

    No, ‘induced traffic’ is the correct technical term, whereby a reduction in generalised cost leads to an increase in vehicle miles.

    Most of the increase in traffic tends to be a) traffic diverting from more congested roads and b) new development, which can now be justified due to the reduction in congestion due to the new roads being built – ironically. A classic example of this is the Newbury Bypass, which locked solid after only a few years.

    Antiplanner wrote:

    “In fact, the real goal of congestion pricing is to increase traffic flows and allow more people, not less, to drive during rush hours. As Vanderbilt himself notes, when freeway speeds are 55 mph, a single lane can move as many as 2,400 cars per hour. But at 35 miles per hour, the same lane can move only 1,700 cars per hour (p. 121). If there are 2,000 cars per hour trying to get through the lane and one of the slows to 35, even for an instant, suddenly the lane’s capacity is below the demand and speeds will remain at or below 35 until the demand falls below the new capacity. (Traffic engineers call this “level of service F.”)
    The purpose of congestion pricing is to make sure that volumes remain low enough that “incidents” (such as one car slowing down) do not cause capacities to fall below demand. A well-designed congestion pricing system can therefore maintain throughput at, say, 2,000 cars per hour instead of the much lower throughputs that would result if speeds fell to 20 or 30 mph. Potentially, then, congestion pricing can effectively double rush-hour highway capacities.
    Maybe if we did a better job of explaining how congestion pricing will increase, not decrease, people’s mobility, there would be less opposition to the idea. Unfortunately, some people do want to use congestion pricing to reduce driving (not necessarily including Vanderbilt), which means they would charge much higher rates than needed to keep traffic flowing so that they can divert the funds to expensive rail transit projects.”

    I have no idea what this is about. Road pricing is an attempt to reduce the flow of traffic at certain times of day, by pricing them off the road – or in the modern spin, ‘sending them pricing signals’. The saturation flow of a 30mph road should be north of 1900 cars per hour. I don’t know where he got 1700 from. Saturation flows on motorways are better (closer to his figure) because the lanes are wider, the roads are wider, offside lanes do better, and car drivers are more aggressive.

    In the UK, motorway speeds are often reduced to 50mph, not because the capacity is higher or lower, but to reduce the effect where one driver brakes slightly, and the effect is amplified as the braking moves down the road, until some vehicles have to stop altogether. This is known as a ‘shockwave’, and is prevalent on high speed roads at high flow densities, and often where motorways merge.

    No matter how much spin is put on it, road pricing is about pricing poorer car drivers off the road. These people can just about afford to keep a car on the road, until the congestion pricing mob take the car off them. For the car driver’s own good.

    Mike wrote:

    “Heck, I wouldn’t take transit if it weren’t a cheaper option than driving. It sure does take longer, so something has to balance out that shortcoming.”

    That’s about building transit as a complete solution, wrapped up in a ribbon – electronic ticketing, real-time information, separating transit from the car flows (and the associated congestion). This all costs money – particularly where rail is used. Usually, transit is put forwards as a poverty-specced thing for people who can’t afford cars, generally using crude diesel buses. And then, to some people’s great surprise, car drivers don’t use transit.

    In Leeds, they use bus gates. As the bus approaches the junction, down the median, it is detected, and traffic lights automatically hold cars back away from the junction, allowing the bus to slip out onto the main road, and quickly through the junction. In some cases, a signalised pedestrian crossing is used to stop the traffic, and the buses moves round behind it. Result – a massive increase in bus use, at a time when bus usage is generally falling.

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