By Dom Nozzi
Many of us who seek to make our world more conducive to happy people rather than happy cars are adamant about the importance of slowing car speeds in communities.
Residential streets typically do not promote the problem of high-speed, free-flowing traffic, but sometimes they do act in such a way when they are used for “cut-through” trips or if they are relatively large neighborhood streets which “collect” traffic fed from smaller streets in the neighborhood (usually called “collector” streets).
Lowering the average motorist speed is one of the most essential ways I can think of to improve quality of life. And the most effective way to do that is through calming strategies which design the street to force slow car travel. It is critical that we LOWER THE EXPECTATION of motorists to be driving at high speeds. High speed car travel in a community should not be considered the “default” way for a motorist to travel.
Tragically, conventional traffic engineers have designed our streets for the past 100 years to promote high-speed travel – even on what should be quiet, low-speed streets. The result is that too many motorists now believe that relatively high-speed driving is the norm.
If we instead start designing our communities so that, eventually, most streets in a community are designed for slow car travel, general expectations will evolve so that a motorist realizes that the normal manner of driving is to drive slow (except on interstate highways, of course). With such an expectation, there will be significantly less road rage (and related hostile driving) in calmed areas, because the motorist EXPECTS to drive slow.
Designing streets for slow speeds is particularly important on residential streets, because such streets are the places where we most expect children and seniors to be, and where people are in homes and bothered by the noise of high-speed car travel. We also need to slow cars on the BIG roads in our community to ensure we solidify a general motorist expectation that they are driving in a slow speed community.
“Road rage” and fast driving are NOT genetically programmed into humans. A slow-speed community is NOT unrealistic.
In a discussion about slower car speeds, it is important to note that speed limit signs have little or no impact on how fast a motorist drives. Average driving speed on a street is dictated by the “design speed” of the street. The conventional traffic engineering philosophy is to assume that safety is best achieved by designing the “forgiving” street. That is, to design the street so that the motorist is “forgiven” if they, say, drive too fast and lose control of their car.
What this means is that the street is made wide and obstructions are kept away from the shoulders so that a fast, out-of-control motorist will not smash into anything.
Unfortunately, this fails to take into account the motorist psychology. If you design a street for safe driving at 40 mph, the average motorist will drive 40 mph, even if the posted speed limit signs say 30 mph, because average driving speed is determined by the maximum speed a motorist feels comfortable driving.
Typically, this philosophy means that a street with a speed limit of 30 mph has been designed with a “design speed” of 40 mph. We should not be surprised when a large number of motorists drive 40 mph on such streets. Enforcement is nearly impossible, short of a police state.
Therefore, in my opinion, the “forgiving street” philosophy gives us LESS safety due to higher speed (and more inattentive) driving.
The effective solution for slowing cars is to “retrofit” our streets (including residential streets) with calming designs that force cars to slow down (which is why things like speed humps are often called “sleeping policemen”).
However, “vertical” treatments like humps are almost never, if ever, appropriate for streets (including residential streets) – particularly those that are on designated emergency vehicle routes (where calming needs to be carefully designed to not excessively impede such vehicles).
In the case of such routes, “horizontal” calming is usually called for. Horizontal treatments include such things as curb extensions or other forms of street narrowing, as opposed to “vertical” calming like humps.
Does Traffic Calming Increase Air Pollution?
A common objection to traffic calming is that air emissions will increase due to “stop and go” traffic that is induced by calming. But this concern makes the mistake of being overly reductionist. Peter Newman and Jeffrey Kenworthy effectively point out why reductionism in this case leads to erroneous conclusions. Newman and Kenworthy correctly point out that those who fear higher emissions due to calming forget about changes in motorist behavior that occur with calming. Reductionist thinking in this case only looks at what is coming out of a tailpipe of individual cars.
But Newman and Kenworthy, take a broader and more accurate view by pointing out that changes in travel behavior (caused by higher development densities, shorter travel distances, congestion, calming, etc.) completely swamp any air pollution gains that can be realized from individual cars that have less stop-and-go travel.
I will grant that it is possible there will be “micro-level” increases in air pollution levels due to calming. But at the “macro” (community) level, I’m convinced there is a net reduction in air pollution. That is, there is LESS air pollution at the community level.