Can Roads Control Your Driving? The answer is YES

 
Where I live, we like our roads WIDE and FAST. Take, for example, the road pictured above -- posted at 25 mph and four lanes. Perhaps 30 cars per day travel on this road. Do you think they see the speed limit sign or the myriad factors that make this road feel ripe for 50-60 mph?

That's design speed - a concept, I was surprised to learn, that a 17-year Plan Commission member in my city was unaware existed.

Yes, POSTED SPEED and DESIGN SPEED are indeed two completely different things. If you live in a suburb, try driving the POSTED SPEED for a while and see how long it takes for cars to stack up behind you. And start using their horns.

Forward-looking communities understand and control DESIGN SPEED, defined by the AASHTO Green Book as "the maximum safe speed that can be maintained over a specified section of highway when conditions are so favorable that the design features of the highway govern." In other words, it's the speed at which you feel safe driving on a given road due to it's width, sight-lines, lack of turns, etc.

Unfortunately, the winding, wide roads in residential subdivisions encourage high-speed driving. And an enormously hazardous environment for kids and non-vehicular traffic (walkers and bikers).

The new goal is to create roads that enforce a lower design speed. Toward that end, it's time to make sure local Plan Commissioners -- even multi-decade veterans who can quote the UDO from memory -- are made aware of the concept and begin to make recommendations to developers (like insisting on buildings close to the street when possible) that are consistent with the goal.

The Infrastructuralist has a great piece on new research that shows safety-enhancing road design works:

New research from the University of Connecticut suggests that minor reductions in vehicle speed are possible through changes in the street environment. Through the use of roadside parking, tighter building setbacks, and more commercial land uses, road designers can make drivers  subconsciously drive more slowly, according to a study of hundreds of roads in Connecticut. It’s a revelatory demonstration of the power of design to change the way people interact with transportation.

For years, the Dutch have been telling us about “self-explaining” roads. According to experiments conducted in the Netherlands, drivers are more likely to follow cues like narrow lanes and street trees than they are to respond to decreases in speed limits. The implementation of these self-explaining streets across that Northern European country has resulted in a significant reduction in automobile collisions, to a point where Dutch drivers are less than half as likely as their American counterparts to die in a road accident. (For a closer look at auto accidents around the world, click here.)

Nevertheless, U.S. transportation engineers have generally ignored this European experience, focusing instead on “forgiving highways” that overcompensate for drivers’ mistakes through generous curve radii and wide lanes.

Unfortunately, while these efforts have been successful in reducing fatalities on the high-speed Interstate system, they’re far less effective for urban situations, where they generally encourage drivers to go faster, putting more drivers, as well as bikers and pedestrians, in danger. Lowering the speed limit has rarely worked to reduce drivers’ speeds, especially for chronic speeders.

And the suburbs do indeed spawn faster drivers:

The study also demonstrated conclusively that, compared to urban and other commercial environments, suburban neighborhoods had higher driving speeds — likely because of fewer distractions for drivers. Similar data showed that the further buildings were set back from the roadways, the faster drivers moved. In other words, the more built-up the environs of a road, the slower drivers went.

So the conclusion is this: People can be induced to reduce their driving speeds when cars are parked along the roadways, when buildings are close to the street, and when those buildings include commercial rather than residential activity.

via www.infrastructurist.com

Comments

[Andrew W]

You're right, it's surprising this isn't obvious to suburban planners. It reminds me of The Design of Everyday Things, where Donald Norman introduced the term "affordances". A wide, long road with no sidewalks affords for high-speed driving. A narrow road with marked intersections, parked cars, and sidewalks, where the presence of empty cars and chatty walkers signals a need for a little more caution, doesn't afford for high-speed driving.

As Norman famously described, a raised bar across a door affords for pushing, even if there's a big sign saying "PULL". Planners shouldn't be surprised when they offer a race track and get racers.

[John Michlig]

That's a very good point: We make things, and then those things often make US.

It's doubtful that most city engineers (never mind Plan Commission members) are students of the sorts of disciplines Donald Norman describes. On the Plan Commission, especially, there are rampant "seat of the pants" assumptions made as though they have some basis in measurable reality.

[Carry Bacot]

It's all about having a proper mindset, indeed. It can be hard to think of caution when the road beckons with big spaces. Road makers must aim for efficiency in this case. Areas high in population must have indicators that safe driving is vital.