Archive for the ‘Street Design’ Category

Counter-intuitive traffic

July 20, 2009

Perhaps the most confusing element in convincing the public about certain traffic improvements is the fact that traffic often behaves counter-intuitively.  We often think of traffic like water – if you remove some capacity from a stream, that water has to go somewhere.   In fact, traffic often behaves more like a gas – it expands to fill the volume given.  Conversely, when space is restricted, the same amount of gas will still fill that volume.

Obviously, this is a gross oversimplifaction of things.  The context of each situation matters a great deal, but for the most part, traffic fills the space available to it.

With that in mind, there are a couple of nice pieces circulating about traffic and how we deal with it:

Streetfilms visits the closures of Broadway at Herald Square in New York, noting how this particular closure has both increased available pedestrian space as well as improved traffic flow by vastly simplifying complex turning movements.

In a similar vein, Tom Vanderbilt (of Traffic fame) has a great piece up at Slate concerning the rise of the roundabout and some of the counter-intuitive effects they have.  Vanderbilt notes the disconnect between our common perceptions about roundabouts and the reality.  For example, we think they’re unsafe when they’re actually more safe.  We also think they’re slow (which they often are) yet they manage to move more traffic through the intersection in the same period of time – slower top speed, but faster average speed.

Ryan Avent has a couple of interesting posts on the potential for charging for roads based on vehicle miles traveled, rather than gallons of gas consumed.

The first concerns tolling technology.  The University of Minnesota has a cheap and easily installed device that could track miles traveled using mostly existing technology from on board car computers and SMS text messaging – thus using cell phone services rather than GPS based technology.  Such a device would seem to be both more cost-effective than GPS based systems and would also ameliorate some of the big brother privacy concerns with a VMT tax.

Discussion in the comments quickly returned to the idea of why a VMT tax is even necessary – why not just increase the gas tax? Avent’s second post takes this question on:

Several things to note. First, as I mentioned in the original post, this technology might also make it easier to do congestion tolling, which would be of enormous economic and environmental benefit. Second, I think we should increase the gas tax, whether or not we adopt a VMT. Oil dependency is pretty obviously a nefarious economic force, and I think it’s worth encouraging drivers to get off the black stuff. I’m also clearly in favor of carbon pricing, which would have a small but positive impact on gas prices.

Third, increasing gas taxes isn’t a very good way to pay for long-term infrastructure expenses, because higher gas taxes make people use less gas. So you increase the tax, and then people substitute away from the tax, reducing revenue, and then you can increase the tax again, and consumers will substitute away even more and revenues fall again, and so on. Higher taxes encourage efficiency, then a move to hybrids, and then a move to electrics, at which point you no longer have any tax revenue.

All good points.  Raising the gas tax now will help bridge the gap we have in transportation financing, as well as provide some much needed incentives to continue the shift towards both driving less and doing so in more fuel-efficient vehicles.  But this obviously is not a long term solution, and that’s where a VMT tax comes into play.

The devil, of course, is in the details.  Using VMT as a revenue stream is a great idea in the abstract, but that presumes heavier, road-damaging trucks will be taxed more than light cars.  As Ryan notes, linking such a mechanism with the ability to charge tolls is also an intruiging idea, as not every vehicle mile is equal.

Nevertheless, this will be the front line for the new transportation bill.  Without a stable funding source, financing infrastructure improvements will be difficult.

Also on the Avent watch – Ryan has a nice smackdown at Streetsblog of some conservative think tank dreck on the transportation front.

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