What driver hasn’t impatiently waited to make a left-hand turn, while anxiously anticipating a quick dash between two oncoming cars? It’s a dangerous move that the National Highway Traffic Safety Administration (NHTSA) says is involved in 61 percent of crashes that take place while turning.
A study by New York’s transportation planners also concluded that left-hand turns were three times as likely to kill pedestrians as right-hand turns, and 36 percent of fatal accidents involving a motorcycle involve a left-hand turn in front of the motorcycle.
Even when there is a left-turn lane and traffic signal, if your judgement is off or visibility is poor you are risking a collision. AAA advises drivers to signal a left-hand turn at least 150 feet in advance of the intersection, and yield the right of way to other traffic. To safely complete a left-hand turn, you must consider:
- The speed of oncoming traffic
- The time involved to complete the turn before the light changes
- Whether or not there are other vehicles, bicycles, motorcycles or pedestrians in the path
Whenever possible, it is always better to avoid a left-hand turn by using a different route.
UPS Finds a Way to Eliminate Left-Hand Turns
While considering the danger of left-hand turns, United Parcel Service also was concerned about the time its drivers spent at each left-hand turn intersection. Because idling and waiting to turn left takes time and uses fuel, in 2004 UPS began to require that its drivers avoid turning left whenever possible.
The company later added to its trucks an onboard GPS navigation system called ORION (On-Road Integrated Optimization and Navigation), that tells drivers the best route to take using right turns. By choosing driver routes that minimize and sometimes eliminate left-hand turns, UPS has been able to save millions of gallons of fuel and decrease driver time in making deliveries.
How do UPS drivers do it? Instead of waiting to make a left turn, a driver continues ahead to the next intersection, turns right, and then makes two more right turns around the block, using the traffic light to go straight across the intersection. While some left-hand turns are unavoidable or not always necessary, such as in residential neighborhoods where traffic is low, when possible this maneuver can help any driver avoid accidents, while saving time and fuel.
Left-hand Turns on and off Highways Are Especially Dangerous
Higher speed limits on many highways across Central and Eastern Oregon went into effect in 2016, pushing the maximum allowable speed limit to 65 mph on U.S. Highway 20, which was a contributing factor in this accident.
On March 24, 2017, Oregon State Police Troopers and emergency personnel responded to a report of a fatal two-vehicle crash on U.S. Highway 20E in Brothers, Oregon. An investigation of the accident revealed that a 2005 Nissan Altima, while traveling westbound, was struck by an eastbound 2010 Toyota Rav4 attempting to make a left-hand turn into the Brothers Rest Area. The Toyota’s front passenger side corner impacted the front of the Nissan, causing extensive damage. One of the passengers suffered fatal injuries as a result of the collision.
Diverging Diamond Interchange Replaces Left-hand Turns
In 2009, the State of Missouri constructed the first Diverging Diamond Interchange (DDI), also called the Double Crossover Diamond Interchange (DCD) to solve the problem of dangerous freeway left-hand turns. Since then, more than 80 have been built in the U.S. Due to its safety, efficiency, and cost-effectiveness, the DDI has become a popular choice for upgrades to high volume intersections.
A traditional left-turn intersection uses a 3-phase traffic signal with a separate left turn phase and 26 points of conflict between vehicles. With a Diverging Diamond Interchange, through traffic and left turns happen at the same time, eliminating the need for a separate left turn phase, and reducing conflict points to 14, to reduce collisions by 50% and minimize their severity.
A DDI is more efficient with fewer signal cycles and less chance for conflict and accidents because it allows for free-flowing movements that aren’t conflicting with other traffic movements. One direction moves at a time, clearing out all the traffic, while avoiding wait time for a left-turn signal.
Washington State’s First DDI to Be Completed in 2018
Washington State Department of Transportation (WSDOT) plans to upgrade the existing Marvin Road interchange in the rapidly growing Hawks Prairie business district in Lacey to a Diverging Diamond Interchange. Signs and large, clearly marked lines, stripes, and lane arrows will direct traffic, guiding drivers through intersections, to increase safety and improve traffic flow. A DDI is also planned for the I-90/Highway 18 interchange, east of Issaquah.
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