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City of Seattle

Public health effects of center turn lane projects

Center turn lane projects – sometimes called a “road diet” or “rechannelization” – convert four-lane undivided roads into three-lane roads featuring a center turn lane, bicycle lanes, sidewalks, and/or street parking. Center turn lane projects improve the safety and efficiency of roadways, while also improving the health and quality of life of roadway users and neighborhood residents. How do these changes occur? They happen through two primary means: prevention of unintentional injuries and creation of an environment that makes physical activity an easier choice.

Center turn lane projects decrease the rate of motor vehicle collisions, which are the fourth leading cause of injury-related death in King County. Fewer lanes mean fewer lane changes for drivers, fewer lanes for pedestrians to cross, and lower overall driving speeds. Encouraging drivers to follow the speed limit is no small matter – consider that excessive speed is a factor in almost one-third of fatal crashes and that pedestrians hit at 40 miles per hour have only a 15% chance of survival.

The traffic on NE 125th paints a concerning picture for public health and safety. For the three year period between January 2007 and April 2010, there were 153 collisions on this road, and people were injured in more than half of the collisions, far more than the rate of injury on similar arterials. Sixteen of these collisions involved pedestrians and bicycles – in fact, 3 were hit and runs. A rechannelization project here would reduce speeding along the corridor and improve overall safety.

Other center turn lane projects in Seattle have lead to significant safety improvements. After the 2007-2008 Stone Way rechannelization, there were 14% fewer overall crashes, 33% fewer crash injuries, and fewer bicycle collisions per trip. Collisions involving pedestrians have been reduced by 80%! Roadway speed is also closer to the posted speed limit. Even with all these safety improvements, the corridor capacity remains the same and traffic on adjacent streets did not increase.

Center turn lane projects also help resident’s live active, healthier lives. Center turn lane projects often include improvements to sidewalks, crosswalks, and bike lanes to encourage walking and biking. And giving people the option for physical activity can help combat obesity and associated conditions such as heart disease and diabetes. It’s also good for kids’ health. Parents who perceive local traffic as dense and dangerous are less likely to let their children walk or bike, so it comes as no surprise that children who live in areas with sidewalks and controlled crossings are more likely to walk or bike to school.

Despite their clear benefits in many circumstances, center turn lane projects aren’t always the best solution. On busy roads that are at capacity, they may lead to stop and go traffic which increased emissions. Center turn lane projects also don’t work in areas like industrial and warehousing districts where narrow roads may cause problems for freight mobility.

But the center turn lane project on NE 125th is important to the safety of commuters and area residents, and with careful evaluation and planning, it will create an environment that works for drivers, bikers, and walkers alike.

Tony Gomez
Manager, Violence and Injury Prevention
Public Health-Seattle & King County

Posted by: Robert Cruickshank

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