Friday, January 29, 2010
 

Tysons Neighborhood Traffic Impact Study

The Neighborhood Traffic Impact Study developed by Fairfax Dept. of Transportation, was conducted to assess the impact of future development in Tysons Corner on neighboring communities. These are the communities where using a bicycle to get into and around Tysons should be a viable option for many short, local trips.

As with many "traffic" studies, there is no mention of bicycling and walking. The contractor selected 19 intersections for analysis, using two levels of future density in Tysons and looking at the modeled impact of that development on traffic delay (Level of Service or LOS). Where intersections "fail" with a low LOS, mitigation measures, such as added through or turn lanes, are recommended. The impact of these "improvements" on pedestrian and bicycle levels of service isn't considered.

As Greater Greater Washington explains in The only thing we have to fear is fear of traffic, this narrow view of how the world works isn't very effective when it comes to analyzing how cities work:
The math seems simple. If you build new houses, stores or offices, they will generate a certain number of trips. Roads have set capacities. The added trips will therefore increase congestion and decrease Level of Service (LOS). To avoid congestion, many areas have Adequate Public Facilities ordinances requiring developers to widen the roads.

That's a straightforward formula for adding suburban sprawl. It's the system that built Tysons Corner. But strangely, when a plan comes up for building a real city, people balk. It could never work. It'd generate way too much traffic.
Despite increased growth in the Ballston Corridor, traffic congestion has not increased; people live in mixed-use communities near transit and they walk, bike, and take transit. These factors are often not properly handled with current traffic models.

See a related post at SF.Streetsblog, Paradise LOSt (Part I): How Long Will the City Keep Us Stuck in Our Cars?.

[It should be noted that despite the above rant on LOS, the conclusion of the Traffic Impact Study was that: "revising the existing Comprehensive Plan by considering the GMU High Land Use Alternative will not cause any significant traffic impacts in the study area."]

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Sunday, November 15, 2009
 

Traffic notes, part 2

Earlier we posted some quotes from the book Traffic: Why we drive the way we do (and what it says about us). It's an excellent book with many insights into what happens when people get behind the wheel. Here are a few more quotes from the book:
Car companies would rightly be castigated if they advertised the joys of drinking and driving. But as a survey of North American car commercials by a group of Canadian researchers showed, it is quite acceptable to show cars being driven, soberly, in ways that a panel of viewers labeled "hazardours." Nearly half of the more than two hundred ads screened (always carrying careful, if duplicitous, disclaimers) were considered by the majority of the panel to contain an "unsafe driving sequence," usually marked by high speeds. pp. 66, 67

"Baker's law," named after crash reconstructionist J. Stannard Baker, notes that drivers "tend to explain their traffic accidents by reporting circumstances of lowest culpability with credibility" —that is, the most believable story they can get away with. p. 72

"If you're limited in how many things you can pay attention to, and attention is a gateway to consciousness, then you can only be aware of a limited subset of what's out there." Inattention blindness, it has been suggested, is behind an entire category of crashes in traffic, those known as "looked but did not see accidents." p. 83

This attention disorder could also help explain the "safety in numbers" phenomenon of traffic, as described by Peter Lyndon Jacobsen, a public-health consultant in California. You might think that as there are more pedestrians or cyclists on a street, the more chances there are for them to be hit. You are right. More pedestrians are killed by cars in New York, City than anywhere else in the United States. But as Jacobsen found, these relationships are not linear. In other words, as the number of pedestrians or cyclists increases, the fatality rates per capita begin to drop.

It is the behavior of drivers that changes. They are suddenly seeing pedestrians everywhere. The more they see, typically, the slower they drive; and, in a neatly perpetuating cycle, the more slowly they drive, the more pedestrians they effectually see because those pedestrians stay within sight for a longer period. p. 85

Dutch cyclists are safer simply because there are more of them, and thus Dutch drivers are more used to seeing them. ...Gainesville, a college town with the highest cycling rate in the state, is in fact the safest place to be a cyclist. p. 86

Studies have shown that drivers seated at higher eye heights but not shown a speedometer will drive faster than those at lower heights. p. 94

We "overdrive" our headlights, moving at speeds that would not allow us to stop in time for something we saw in the range of our lights. p. 98

Studies have shown that pedestrians think drivers can see them up to twice as far away as drivers actually do. According to one expert, if we were to drive at night in a way that ensured we could see every potential hazard in time to stop-what is legally called the "assured clear distance"-we would have to drive 20 miles per hour. p. 99

The "slower is faster" idea shows up often in traffic. The classic example concerns roundabouts. Many people are under the mistaken impression that roundabouts cause congestion. But a properly designed roundabout can reduce delays by up to 65 percent over an intersection with traffic signals or stop signs. p. 124

One of the curious laws of traffic is that most people, the world over, spend roughly the same amount of time each day getting to where they need to go. Whether the setting is an African village or an American city, the daily round-trip commute clocks in at about 1.1 hours. p. 131

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Saturday, September 26, 2009
 

Traffic notes, part 1

Based on hearing a good review from a fellow FABB member, I've just finished reading an excellent book, Traffic: Why we drive the way we do (and what it says about us) by Tom Vanderbilt. There's a lot of good information about bicycling in the book, along with many other useful and interesting facts about traffic around the world. I found myself underlining many passages and writing notes in the margin, so I thought I would occasionally pass on some of the better points on the FABB blog.

Henry Barnes, the legendary traffic commissioner of New York City in the 1960's, reflecting on his long career in his charmingly titeld memoir The Man with the Red and Green Eyes, observed that "traffic was as much an emotional problem as it was a physical and mechanical one." People, he concluded, were tougher to crack than cars. "As time goes on the technical problems become more automatic, while the people problems become more surrealistic." That "surrealistic" side of traffic will be the focus of this book. p. 13

The average American, as of 2005, spent thirty-eight hours annually stuck in traffic. In 1969, nearly half of American children walked or biked to school; now just 16 percent do. From 1977 to 1995, the number of trips people made on foot dropped by nearly half. This has given rise to a joke: In America, a pedestrian is someone who has just parked their car. p. 16

Fast-food restaurants now clock as much as 70 percent of their sales at drive-through windows. An estimated 22 percent of all restaurant meals are ordered through a car window in America. Starbucks, which initially resisted the drive-through for its fast-food connotations, now has drive-throughs at more than half of its new company-owned stores. p. 16

When bicyclists violate a traffic law, research has showed it is because, in the eyes of drivers, they are reckless anarchists; drivers, meanwhile, are more likely to view the violation of a traffic law by another driver as somehow being required by the circumstances. pp. 23, 24
Vanderbilt also maintains a good blog about traffic, How We Drive.

He also writes a column in Slate. His latest is entitled iTransport: Could iPhone apps change the way we travel? Among the topics covered are Car apps, Public Transit apps, Bicycle apps, and Walking apps. "I've particularly enjoyed B.iCycle's app, which tracks variables like average speed and altitude climbed, then sends an e-mail report at the trip's conclusion. REI's BikeYourDrive features a nice twist on the concept, showing the advantage in cost, carbon emissions, and calories of a particular bike trip versus the automotive alternative."

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