How to design streets for calm driving

Some streets need to be engineered for slow motoring. Believe it or not, there are many "industry approved" ways to make it happen.

A house limits your ability to run. You walk from the bedroom to the kitchen. Guests visit, and they walk around and sit down. 

An open field gives you space to go as fast as your body motor allows. Friends and strangers can run with you, or in different directions. 

Some streets need to be engineered for slow driving. Some parts of the neighborhood are intended to be a living room, not an open field. 

You might think enforcing speed limit signs is the only practical solution, and focusing on street design is an expensive alternative. After all, "It's not like engineers purposefully design streets for speeding." But that's exactly what they do. 

It's common for streets to be engineered for people to comfortably drive 10 mph over the legal speed limit. I do it all the time. Sometimes I use cruise control because normal arterials are just so easy to speed on. "They were speeding, but it wasn't dangerous speeding" is a mainstream health hazard of polite society. Speed kills. 

AASHTO says what your local transportation or public works department avoids admitting:

Speed reduces the visual field, restricts peripheral vision, and limits the time available for drivers to receive and process information.

Modern streets are engineered to comfortably speed. Nevermind the law’s posted speed limit, the road itself encourages bad behavior. Civil engineers are allowed to use good judgment, but they need to be reminded. Even the much-hated-by-urbanists AASHTO Green Book allows for safe street design. (It costs a fortune, so find a library copy.)

Engineers who read the Green Book will find this reminder about using judgment that goes beyond tables or graphs (emphasis mine):

Design speed is a selected speed used to determine the various geometric design features of the roadway. The selected design speed should be a logical one with respect to the anticipated operating speed, topography, the adjacent land use, and the functional classification of the highway. In selection of design speed, every effort should be made to attain a desired combination of safety, mobility, and efficiency within the constraints of environmental quality, economics, aesthetics, and social or political impacts.

It’s still a highway-minded narrative, but there’s flexibility in the language. You can’t possibly measure social impacts from Table 2.7 or Figure 4.1. So when professional engineers blame AASHTO for not implementing traffic calming measures, you know better. AASHTO expects licensed professionals to be conscientious problem solvers, not automated copy/pasters. 

One last Green Book gem:

It is desirable that the running speed of a large proportion of drivers be lower than the design speed.

If civil engineers had to pay a percent of speeding fines issued on their streets, they’d immediately change their office behavior to calm our driving behavior. In the meantime, it’ll take some effort on our part to remind the professionals about their industry-approved traffic calming techniques. 

• Narrow lanes. 10-ft instead of 12-ft, even on the busy streets. Restriping is cheap and effective.

• Fewer lanes / road diet. Safer for people behind the wheel and people walking.

• Wide sidewalks. Most standard sidewalks aren’t even wide enough for two people to comfortably pass each other.

• Textured stripes / rumble strips. Used to transition from high-speed to low-speed areas.

• Textured pavement. Cobblestones aren’t your only option in the 21st century.

• Diverters. Popular on bike boulevards to prevent drivers from going straight across an intersection.

• Midblock crossings. Break up “super blocks” with flashing beacons for pedestrians.

• On-street parking. But it better be replacing car storage, not adding more!

• Chicanes. The s-curve feel that makes driving slightly uncomfortable.

• Trees. Along the sides and in the center of traffic circles and roundabouts.

• Roundabouts. Or traffic circles, depending on the type of intersection.

• Bump-outs / chokers. They’ll show tire marks from all the rubs, but that’s progress. Use at intersections or midblock.

• Bollards. For endless smiles, follow World Bollard Association on Twitter.

• Tight corners. 90 degrees if you please. No swooping curves. 

• Street furniture. Benches, lights, trash cans, restaurant signs, bike racks, etc.

• Raised intersection. Pricey but effective way to put pedestrians on a pedestal.

• Raised crosswalk. Like a speed hump wide enough for people to walk across.

Here are some resources to get you familiar with traffic calming:

1. FHWA

2. AASHTO

3. ITE

4. NACTO

5. Global Designing Cities Initiative