Speedbumps and the city’s carbon footprint?
We have a mail list for the back channel at InBerkeley.com, and from time to time a question comes up that requires research. If the question is interesting, my first impulse is: Write It Up!
Now, this is the result of 12-plus years as a blogger. I know my community loves interesting questions, and we have an informal approach on Scripting News that I’d like to port to InBerkeley.com.
So, in that spirit — here’s a question posed by my colleague Mark Haas.
Do Berkeley’s infamous speed bumps, traffic diverters and other traffic-related policies, like politically-motivated, too-low speed limits raise the city’s carbon footprint?
We just need a qualified author. Anyone know any traffic engineers, or perhaps someone at the UC Berkeley Institute for Transportation Studies? Other experts?
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http://www.bromleytransport.org.uk/Speed_Humps_USA.htm
Funds allocated for a traffic calming experiment by the Congestion Mitigation and Air Quality (CMAQ) Program to the City of Portland, ME were rescinded when it was shown that the project of humps increased emissions by 48% without taking into consideration increased emissions from braking and acceleration required to negotiate the devices. The State of Maine has been ordered under the federal Clean Air Act to show evidence of compliance in reducing pollutants. Section 113, “Federal Enforcement,” states fines including imprisonment will be levied against entities responsible for knowingly increasing the release of pollutants into the air in cities on federal notice to improve air quality. The experiment has not been removed.
An Austrian study, in 1994, using a mobile exhaust fume measuring-device registered an increase in vehicle emissions of ten times on streets with speed humps.
The Transport Research Laboratory (TRL), a research agency of the Department ofTransportation in the United Kingdom, conducted emissions tests in 1997 on streets with road humps and found the following results as reported in TRL Report 307:
“Schemes with a 75 metre hump spacing . . . showed increases in CO and HC of around 70 – 80% and 70 – 100% respectively, and an increase in CO2 of around 50-60%. Nox emissions were predicted to be about 0-20% lower after calming.”
To calculate the possible effect of smoother driving after the installation of humps (without braking and acceleration) the TRL measured the change in emissions associated with moving from a constant speed of 30 mph to a constant speed of 20 mph and found the following results:
CO and HC increased by 40 – 80%, CO2 by 30 – 40% and NOx by 20 – 30 %.
A more recent study by the TRL, Report 482 in 2001, registered increases in all emission pollutants after traffic calming:
For petrol catalyst vehicles: CO 59%, HC 54%, NO2, 8%, CO2 26%
The study states that speed humps created the largest increase in pollutants of all calming devices tested.
And lastly:
The UK’s AA [Automobile Association] did a bit of research on fuel consumption for cars at the Millbrook Proving Ground and found that a typical mid-size car running at a constant 50kmh did 4.7L/100km. However when the same car had to slow down and speed up at speed bumps, it only managed 9.11L/100km.
Put that into carbon figures and you get 113 g/km of CO2 at a constant 50kmh, or 211 g/km over speed bumps.
So a kilometre of road with speed bumps creates an extra 0.1kg of CO2 for every car that uses it.
Hmm. Won’t that be an essentially impossible question for even an expert to answer? Honestly, by what methodology do you expect an answer to be derived?
Traffic calming systems likely do, as the previous comment says, increase the emissions of individual cars which travel over them. Here in Berkeley, though, we have a grid system of roads in the flats, with several non-calmed major corridors. Anecdotally, I observe that the calming features tend to direct traffic to those major, higher-speed corridors. At the same time, they encourage much greater use of bicycles. So, while an individual car going over speed bumps might double its emissions, it’s harder to say how many fewer car trips are taken because of the bump or how many car trips stick to faster corridors with no bumps and fewer stop signs or lights.
Berkeley’s typically 25MPH and some places 15MPH speed limit is, indeed, politically motivated. Here on my block the street acts as a playground, pretty much all day during the summer. Basketball, bike riding, scooter riding, skateboard riding, general horsing around — kids ranging in age from about 4 on up. The lower speed limit helps to keep those kids safe. I would not say the limit is “too low” – it’s about right or perhaps even slightly too high for safe driving on this block. To be sure, this is pure politics. “Kid safety first” (and safety for commuters on bikes, for that matter) are not goals that everyone automatically agrees with. It’s just meddling do-gooders with their annoying “pro kid” and “pro cyclist” agendas. No doubt we abuse the political system by imposing our views on others but, hey, we can slug that one out at the ballot box if you have a problem with it.
The real problem that contributes the most to emissions from cars? People rely on them too much and tend to use them in horribly inefficient ways (such as single occupancy). That, not speed bumps, is the big problem to fix.
-t
Mark needs to learn something about posing research questions, namely that there should be a least some semblance of objectivity in their framing. It’s pretty clear that he already has come to the conclusion that Berkeley’s speed limits are too low and that any infrastructure that acts to slow down or otherwise inconvenience cars is undesirable. He is now looking for arguments to support that conclusion.
A better, less leading question might be, “What research exists on the relationship between various traffic policies and carbon emissions?”
While I’m willing to believe that speed humps increase emissions, I do know that the inconvenience of driving in Berkeley leads me and many others to bike or ride public transit instead. Perhaps the streets with speed humps should be closed to cars entirely, or only open to emergency and delivery vehicles.
As for the speed limits, I find that I get the best mileage when I stick strictly to Berkeley’s posted speed limits. Plus I get the added pleasure of pissing off the Type-A drivers behind me who consider 30MPH an affront to their personal freedom.
As stated, it seems Mark is more concerned about driving slow than he is about the environment or the safety of pedestrians and pets. Not to mention the peace of mind of home and shop owners who occupy those roads.
We’ve been requesting speed calming devices from our city for over 3 years now to help with the dangers of speed in our neighborhood. You should consider yourself lucky to have such devices in place.
The emissions problem needs to be solved at the source (the car), not at the safety measures that aid vehicle & pedestrian movement.