Visiting scholar shares how driveways can be made safe for all users
By one count, nearly one in five crashes on city streets is related to driveways. Despite this, driveway design has attracted little attention in transportation circles until recently.
While the needs of different road users sometimes conflict, a smart design often can accommodate all users without much, or any, inconvenience. “If you look to design guidelines years ago, they were assessed solely from the needs of automobile drivers,” Gattis said. “But pedestrians and bicyclists also have to cross driveways. And pedestrians with disabilities of sight, or who are in wheelchairs, have their own problems, many of which can be easily remedied with alternative practices that are no more onerous to design or construct.”
No one sets out to design a bad driveway. “I would guess that somebody just didn’t think about it; it didn’t cross anyone’s mind,” Gattis said. "Design practices that make the roadway easier for drivers, bicyclists and pedestrians to navigate fall into the category of observing how traffic operates and applying common sense to it.”
Gattis himself hadn’t always considered driveways so closely. A practicing design engineer before he returned to school for his doctorate degree, Gattis brought that experience to his studies of access management, the regulation of access to roadways.
“The more I learned about access management, the more I realized how many of the traffic problems I encountered arose from a lack of access management.”
Limiting the number of places vehicles can turn left can, for example, annoy business owners who want to be accessible. But framing the debate as a between safety and convenience is too simplistic, Gattis said. “If you’re the one whose car is getting rear-ended, I’d say that’s pretty inconvenient.”
For safety data, Gattis looked at studies that showed between 11 and 15 percent of urban collisions were related to driveways. Then he took a closer look, finding the role of driveways often overlooked in crash reports. He came up with 19 percent of crashes related to driveways. “The inference is that perhaps driveway-related collisions are underreported in the summary data.”
While safety around driveways is a big problem, solving it isn’t a mystery. “When you control the number of driveways, and the spacing of driveways,” Gattis said, “study after study found that the crash frequency goes down.”
Gattis is co-investigator on an OTREC project with Karen Dixon of Oregon State University exploring how drivers respond to roadways with various driveway access points. The presentations in Corvallis May 16 and Portland May 17 will share lessons from his National Cooperative Highway Research Program project “Geometric Design of Driveways.”
Gattis explores both the spacing of access points and their design. The shape of curbs and driveway connections affect different users differently. For example, an abrupt driveway can be easy for a pedestrian to process but hard for a turning driver. A curved approach, however, stands out well for both drivers and pedestrians.
Too often, Gattis said, these considerations go out the window and developers just select the easiest option to build. “It’s like wearing blinders on a horse if you’re ignoring other factors just for the ease of construction.
“It might be very easy to construct, but for the next 50 years you have to live with something that doesn’t serve users as well.”