green speed bumps and other insanities

The debate around traffic calming is a difficult one, and communities get emotionally charged about the pros and cons of speed humps, four-way stops and other mechanisms to reduce traffic speeds and volumes. In many cases, the need to retrofit calming devices is a result of design failure. The focus on efficient vehicular movement tends to dominate road planning decisions, so that municipalities can get the most out of their investment in road infrastructure and drivers can get where they want to go as smoothly as possible; and this results in more cars and higher speeds, resulting in calls for speed reduction measures.

There is a case to be made for efficient movement to reduce emissions - if you assume that cars are going to be on the roads anyway. Slowing cars down with speed humps increases emissions and noise pollution and vehicle wear and tear. But there are other ways. Driver behaviour is influenced by the width of lanes, the road alignment, whether there are trees and bushes at the side, and other cues that make high speeds comfortable or uncomfortable. It's not just about the pavement; it's an urban design issue. Smooth flow at a reasonable speed is actually best for emissions AND efficiency, and with a bit of design effort this can be achieved.

The bigger picture is that we should be providing more viable alternatives to driving, but if we leave that aside for a moment, and assume that there are places where speed bumps are the only viable solution to resolve existing traffic problems, here's an interesting twist: speed bumps that use the energy from cars to generate electricity.

The speed bump in a large shopping mall can potentially generate 1 megawatt of electricity per day, which in turn can supply electricity to many stores and residential homes. In then near future, shopping malls can generate millions of dollars in clean, free energy.

Actually, there's a flaw in this argument. The energy is not clean - it comes from the car's kinetic energy, which (generally) comes from fossil fuels. So what's really happening here is that we are using petroleum to generate electricity. The cars that contribute to this effort have to use extra energy to recover the momentum lost at the speed bump, so the drivers are paying for the energy that powers the stores or homes through the speed bump. Free energy? I don't think so.

Imagine this on a bigger scale. What if the highways authorities installed devices to harness the gravitational potential energy of cars as they rolled down hills? You pay for the gas to drive up one side of a hill, and give that energy back to the authority by pushing a boom on the way down. The opposite of a ski lift. Just hook yourself in and enjoy the ride. This could be a financial alternative to the toll road, and we might not even complain, since we have to pay for the fuel anyway. And what if our cars are pure electric vehicles, recharged from renewable energy sources? Welcome to the carbon neutral highway.

the bell tolls

People are willing to adopt the "pay-as-you-go" model for all kinds of services and infrastructure, from the telephone to parking lots. But for using roads? Political opposition to road tolls is strong in many countries, but commentators are starting to think that a begrudging acceptance of congestion pricing in some quarters may indicate acceptance - finally - that it's futile to try to keep building our way out of gridlock.

Washington has allocated funds to help states and cities develop congestion pricing systems, and may even apply the same concept to airlines: charge users more to travel in congested corridors, encouraging them to change their route or time of travel.

community pressure for stop signs may be misguided

According to a report prepared by consulting firm Totten Sims Hubicki Associates (City of Oshawa Neighbourhood Traffic Management Guide, March 2002), stop signs are not all they are cracked up to be. This report is not available online, so here are the facts:

"Many people perceive stop signs as the panacea or 'cure-all' to all community traffic problems. However, stop signs result in drivers accelerating and braking, leading to greater fuel consumption, increased air and noise pollution, and higher mid-block speeds. In fact, on a roadway carrying 4,000 vehicles per day, over 15,000 litres of extra fuel would be consumed and over 2,500 kg of extra carbon monoxide would be emitted annually, due to each additional stop sign. (Calculations based on the Canadian Capacity Guide for Signalized Intersections, 2nd Edition, Institute of Transportation Engineers, 1995.) In addition to the environmental effects, City staff are concerned with increased mid-block speed and the potential of non-compliance, which in the long term compromises vehicular and pedestrian safety."

Other studies (Beaubien, Richard F., "Stop Signs for Speed Control?", Traffic Engineering, November 1976.) reinforce the consultant's conclusion that stop signs should not be used as a form of traffic calming. Where they are not warranted for other reasons, all-way stop signs can also result in poor levels of driver compliance (traffic rarely comes to a full stop), with increased conflict and safety hazards. (See also Pennsylvania's Traffic Calming Handbook, Pennsylvania Department of Transportation, Publication No. 383, January 2001.)

Residents may be satisfied that motorists at least slow down at stop-controlled intersections, but drivers tend to increase their speed between stop signs to make up for lost time. The consultant report cautions that, over time, regular users of the intersection will take more and more risks, thus increasing the potential for collisions.