Saturday, April 16

New study sheds light on roadway safety for all

Traffic safety has been one of those long-standing fault lines in the purported war between cars and pedestrians. In the one corner, we have traffic engineers who are given the task of designing roadways to maximize speed and capacity, while maintaining what is considered an acceptable level of safety for motorists. You do this by making the roadway as forgiving as possible with wider lanes, longer sight distances, and nothing to crash into along the side of the road. In the other corner, pedestrian advocates have insisted on slowing cars down with traffic calming, on-street parking, pedestrian signal prioritization and lots of other strategies to look after their own safety. As the story goes, each side is locked in a shouting match over whose safety is the most important.

Design Solutions for Balancing Traffic Conflicts and Speed. Source: Dumbaugh et. al.
But a new study that appears in the Journal of the American Planning Association sheds more light than heat on the subject. Eric Dumbaugh and Wenhau Li found that designs that make the travel safer for any road user make travel safer for every road user. Really, there is no zero sum game. We don’t have to pick one team. Thankfully.

The researchers looked at almost 300,000 crashes in the San Antonio area and considered all of the details of where the crash happened, not just how many cars use the road or how wide the lanes are. They asked: Is this a pedestrian-scaled “Main Street” or is it an arterial lined with strip malls? Are there big box stores around? How many intersections are in the area, and how many people live nearby? Then they considered who was involved in the crash. Two vehicles? A vehicle and cyclist? A vehicle and a tree? With all of these variables in mind, they determined which factors were better correlated with a safer environment … and for whom.

The results may not entirely satisfy either side, but they make sense. Freeways turn out to be pretty safe, showing a relatively small proportion of crashes. This probably has more to do with the lack intersections on highways, than it does the opulent shoulders and smooth grades. With access limited to a few exits and entrances, there are just fewer chances to collide with an oncoming vehicle. But just as the highway engineers may consider theories are vindicated, the research shows that places on the opposite end of the spectrum are just as safe.
The presence of pedestrian-scaled retail uses, on the other hand, was associated with significant reductions in multiple-vehicle, parked-car, fixed-object, and pedestrian crashes. We attribute this to reduced vehicle speeds. Street oriented buildings create a sense of visual enclosure of the street, communicating to the driver that greater caution is warranted, and resulting in reductions in both vehicle speed and crash incidence.”
Consider all of the chaos of a Main Street scene. A driver is trying to parallel park while a cyclist dodges the opening door. Pedestrians are crossing at will, and delivery trucks are backing into their spaces.  Visual stimulation is everywhere. The old engineering models would take all of these inputs and calculate a daily bloodbath, but nothing of the sort is happening. It’s a highly functional environment. The key here is that both the Main Street and the Freeway are relatively safe for all road users, motorists and pedestrians alike (although let’s admit that pedestrian safety on the freeway is purely a function of their non-existence).

The absolute worst places for everyone were the ones that fell between the cracks of the two paradigms. There’s one of these in your town. The wide highway with a traffic light every few hundred feet leading into strip shopping centers. They are designed to be Freeway-esque with plenty of room for you to veer out of your lane, yet with all of the conflicts of cars pulling in and out still there. These precautions are just a cruel trick, inducing drivers to take on more speed than they really should to their own detriment. Pedestrians are caught in the cross-fire with no armor, and before you judge them for having the audacity just to be there, remember that many service-sector workers have no choice. In the twentieth century we dreamed of the best of both words for our roadways – access and speed! - but ended up with the worst of both worlds.

Freeways will still be utilized for those long-distance trips between cities, at least while gas is still relatively inexpensive. They should continue to be designed to handle the high speeds they command, to allow drivers to travel safely. But within highly-concentrated urban areas, mindlessly applying these same standards wrecks havoc. In these cases, a design approach that takes into account the whole context of the street yields a much safer result for pedestrians and motorists alike.


BobandSusie said...

Hi Daniel,

Interesting post, thank you for the information.

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