Safer Streets Require Less Traffic Engineering, Not More

by James A. Bacon

A week or two ago, I lamented the disparity between the high cost of traffic accidents in Virginia and the paltry resources devoted to reducing their number. But to say that insufficient attention is being paid to the issue is not to say that no attention is being paid. According to Virginia’s 2012-2015 Strategic Highway Safety Plan, traffic deaths in the state fell 23% between 2006 and 2010. We are making progress.

Since my blog post, the Hampton Roads Transportation Planning Organization (HRPTO) published its own regional safety study. The HRPTO did a number of worthy things. It mapped the location of accidents across the region and honed in on the worst freeways and intersections that offered the best prospects for improvement. The planners asked a critical question: Which improvements offer the best benefit/cost ratio? As Brian Chenault with the HRPTO summarizes the range of possible solutions: “Recommendations run anywhere from restriping pavement, bicycle and pedestrian improvements, optimizing signal timing, adding additional lanes, trimming vegetation, reducing speed limits, adding extra signage/signals, etc.”

As untutored as I am in the arcana of traffic engineering, it strikes me that the HRTPO has identified a number of projects that will provide considerable bang for the buck, at least as measured by traditional traffic-engineering criteria. Some of the tactics it advances are ideas that I have championed, such as making better use of roundabouts and traffic light synchronization. Its recommendations undoubtedly would amount to a net positive for the people of Hampton Roads — and I hope readers will view it in that light even as I discuss its shortcomings.

The problem with the study is that the authors approach the safety issue from a traffic-engineering perspective. Not surprisingly, every traffic-engineering challenge has a traffic-engineering solution. Indeed, for some safety problems, traffic-engineering solutions are entirely appropriate. But for many, they are not. In many instances, the best solution is precisely the opposite of what traffic engineers recommend.

For purposes of illustration, let us look at the intersection of Mercury Boulevard and Power Plant Parkway, as shown above. (Click for larger image.) This particular intersection averaged 43 crashes per year between 2009 and 2012, the second most of any intersection studied. The HRTPO’s analysis attributes the high accident rate to a variety of micro-factors, which can be summed up by noting that the traffic patterns here are highly complex, leading to a high number of rear-end crashes and side-swipes. The report makes three recommendations:

  • Add a painted triangle yield line with YIELD pavement markings
  • Relocate stop bars
  • Add a flashing “signal ahead” sign
  • Add a pedestrian signal and crosswalk with ladder striping

What’s the common denominator here? It’s the expectation that more signage and clearer road markings will induce drivers to drive more safely.

Now, let’s take a radical leap. At the 2014 Congress for the New Urbanism conference last week, Ben Hamilton-Baillie, an English consultant who specializes in reconciling traffic movement with quality public spaces, showed a clip of San Francisco street traffic filmed days before the 1906 earthquake. There were no marked lanes. There were no turn arrows. There were no traffic lights. There were no street signs. Pedestrians, trolleys, horses, horse-drawn carriages, bicycles, pull-carts and automobiles shared the street. At first view, it seemed like chaos. People were jay walking and standing around in the middle of the street. Cars weaved between lanes. Vehicles made U-turns. It was a traffic engineer’s nightmare. But no one — at least not in this 12-minute film clip — experienced a mishap. Watch the clip. It’s mesmerizing.

Undoubtedly, some accidents did occur in those days and people did get hurt. Such incidents provided the pretext for the traffic engineers to step in. In the 1920s and 1930s, they segregated vehicular traffic from pedestrian traffic — roads became the domain of cars, and people were relegated to the sidewalks. Not only would this arrangement create safer streets, it was thought, keeping people off streets would allow cars to travel faster, thus increasing the carrying capacity of streets and reducing congestion. That is the path cities have traveled for some 80 years now, with the result that contemporary Americans cannot imagine any other way of doing things. Today, the traffic-engineering solution to every problem is more signs, more lane markings, more signals, more information overload.

improve_pavement_markingThe logical result is something like the intersection shown at left, which is pulled from the HRTPO’s list of crash counter-measures under the tactic of “improve pavement markings.” I would argue that the intersection is so complex that there is no way to improve pavement markings. Motorists will be confused regardless. Drivers encountering the intersection for the first time will be befuddled, as will elderly drivers with slower cognitive functioning, as will distracted drivers tweeting on their cell phones. As for marking the crosswalks with ladder striping, that will only confuse drivers all the more while doing little to encourage pedestrians to brave the inhospitable intersection and cross seven to eight lanes of traffic.

What would happen if someone removed all the traffic lights, lane markings and street signs? Would the street devolve into chaos? Some cities in Germany and the Netherlands have experimented with that approach quite successfully. That’s fine for smaller communities with low traffic volumes in isolated locations, one could argue, but is it practical elsewhere?

Hamilton-Baillie helped re-engineer a major intersection in the center of the English town of Poynton where there was both heavy pedestrian traffic and vehicular traffic, including heavy trucks. The roads had been engineered to maximize traffic flow at the expense of walkability. The town ended up with the worst of both worlds: the traffic back-ups were terrible while the shops and businesses in the enter of town went into decline. In desperation, the city shifted to a system of shared space, lower traffic speeds and less signage — the antithesis of the traffic-engineering solution. The result? Watch the video below.

Spoiler: The Poynton redesign was hailed as a success. Pedestrian traffic revived. And, despite the slower speeds, the continuous flow of traffic increased the capacity of the streets. Although they drove more slowly, trucks and cars moved more continuously.

The problem with conventional traffic engineering, according to Hamilton-Baillie, is that traffic engineers don’t take human nature into account. “In the absence of controls, it isn’t as if we don’t know how to behave,” he said. Bringing down speeds to a level where drivers and pedestrians can see each others’ faces changes the dynamic of driving behavior. When they perceive pedestrians as people, not obstacles, motorists drive much more cautiously. “Social protocols are more powerful than traffic regulations.”

In the traffic-engineering paradign, roads are sluiceways in which cars alternate between sitting behind stop lights and driving at 45 miles per gallon in a stop-and-go pattern. You couldn’t design a system more likely to create read-end accidents. Frustratingly, the ubiquity of stoplights means that cars never reach high average speeds. But when you slow down the speeds and introduce bicycles and pedestrians into the equation, the dynamic changes. Drivers become far more cautious, accidents are far less injurious when they do occur, street life is revitalized… and drivers cover just as much ground.

Bacon’s bottom line: We can’t leave traffic safety to the traffic engineers. While an engineering approach like the state highway safety plan and HRTPO study can make roads marginally safer, there are inherent limits to what the traffic-engineering methodology can accomplish. We should look to our own past, or to contemporary Europe, for alternative ways of organizing our streets.