Slower can be Faster
January 9, 2013 | ∞ Kenneth Small and Chen Feng Ng have a radical idea: slow roads can provide faster travel. From their report:
Older urban parkways, such as the Baltimore-Washington Parkway, the Arroyo Seco Parkway in Los Angeles, and an extensive parkway system on Long Island, feature architecturally interesting structures, attractive landscaping, and designs that fit into the surrounding landscape. They also provide ample capacity and are much cheaper than modern Interstates. Such designs are still possible…
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The choice of lane width leads to a tradeoff between free-flow speed and capacity, but the tradeoff is not symmetric. We find that squeezing more lanes into a given road width produces large time savings during congested peak periods. By contrast, wider lanes and shoulders offer only slightly higher off-peak speeds. Thus, the compact design with higher capacity often results in shorter total travel times. Furthermore, people find congested travel especially onerous, making it even more likely that a system of urban roads carrying people at modest speeds will make travel more pleasant.
Compact roads also have considerable environmental advantages. They integrate better into urban landscapes because they accommodate tighter curves and steeper grades. They require smaller structures and less earth moving. Neighborhoods suffer less disruption, an advantage accentuated by the lower free-flow speeds. Therefore, urban residents are likely to benefit from the smaller environmental footprint of these roads as well as from their superior ability to carry high-peak traffic flows.
The key is factoring in congestion. A 3 lane road designed for 60 mph peak speeds will accommodate more traffic in less time than a 2 lane road designed for 65 mph peak speeds using the same pavement width. The slower roads will be more pleasant as well as they can be made to more closely follow the natural contours of the landscape. Of course, making better performing roads is only part of the picture. Connecting two productive places with an efficient and effective road is great, but we must also ensure that the places on either end are productive as well. The most productive places tend to also be the neighborhoods where the automobile has been tamed such that the neighborhood can operate at the human scale rather than the scale of the machine.
Reader Comments (3)
On one level I can appreciate what they are saying. The George Washington Parkway along the Potomac in Virginia is one of the most beautiful roads I've driven on, and I will always support more beauty than less beauty, but I have a problem with the capacity argument, and context would help, but I just don't have the patience to click the link.
If they're talking about new roads to new developments, fine. But if part of the argument is retrofitting or new highways in existing cities I don't think I can get behind that, outside of the beauty aspect. When friends talk about new highway plans or complain about traffic and say the road should be widened, I have often said, "how many lanes of congestion do you want?" If you want 8 lanes of traffic and congestion, build 8 lanes, but don't fool yourself into thinking a new lane or a new highway will reduce congestion. It might for a while, but after a few years that new capacity is taken up with more cars and you're back where you started. I am always very skeptical of any plans to reduce congestion. This is true of transit as well. Don't let anyone tell you a new light rail line will ease congestion on existing roads - a lot of transit lines are sold as a solution to congestion. When the public decides that the transit line doesn't produce the benefits it was sold on, public opinion will be soured on transit, which might be worse than not having the line at all. Once we acknowledge that, we have to think harder about the honest reasons and real consequences of planning decisions.
Isaac - Your comments are all very insightful and I completely agree. I particularly agree that the report misses all discussion on the role of induced demand as it relates to capacity and congestion and, by its very nature, is overly focused on making things better for the car. I linked to it for three reasons:
1) I like the counterintuitive nature of their discussion with actual data that demonstrates that a slower three lane road using the same ROW as a faster two lane road actually facilitates faster travel times for most people do to better being able to handle congestion (better capacity). Transportation planning tends to be counterintuitive and I like to point that out.
2) I like the idea that building in a gentler way (not relying on brute force) can give us a better experience for less money. I think this concept can be extended to apply to the role of the car as well.
3) Any data that calls into question the city destroying "standards" of typical highway design is a step in the right direction. Conventional wisdom needs to be questioned sometimes. I like the idea that the rural parkway is the ideal highway.
That being said, I completely agree that more capacity is rarely what our cities need. I tried to mention that caveat by focusing on roads that connect places but I probably was not explicit enough.
I agree man, we need to question the standards that are so unbending. It's good to see some people thinking outside the box.
On a somewhat related note, thinking of rural areas and edges of cities, I have said for a long time that I wish we would build less of the mega highways that seem to be the default answer to every question and more of the medium capacity roads. I also wish we would embrace roundabouts like they do in Australia. They're stating to be popular here, at least in Maryland, but not for the same purpose. Instead of an expensive highway interchange where two highways meet they just stamp a big roundabout in the intersection and it's done - not for the major freeways, just the minor highways, but it's so amazingly simple and cheap. You get nearly the same capacity for a fraction of the cost.