Eliminating Left Hand Turns

Thesestudies will have areal impact on street design and planning.  The bottom line is that left hand turns are hugelyinefficient during periods of heavy traffic and need to be diverted into rightturn loops.  The saving on fuelexperienced by myth busters is actually a shocking result and informs us justhow much fuel is spent idling while waiting for a traffic signal.

Fundamentally we need to stopcatering to the left hand turn and spend of making the alternates work well.  This means improving the available right handturn corridors so that the traffic can use it smoothly.  It may seem an inconvenience to drivers whowant to go left but we now know better and should we think on it, idling in aleft hand turn lane while waiting for a traffic opening has always beenproblematic.

The direct saving in both fuelusage and accident rates provide a direct incentive to reengineer all such busystreets and theirs feeders.  I know fromexperience that there are plenty of locations were doing a right hand turn isnot particularly practical and this will take time to fix if it can be done.

Yet beginning with the easy oneswill allow us to educate the public.

Obviously this clearly applies to heavily traveled streets and not your typical residential street network.  however, fixing all this will impact on a lot of residential streets to some degree.

JANUARY 10, 2011

Superstreets are thoroughfares where the left-hand turns from sidestreets are re-routed, as is traffic from side streets that needs to cross thethoroughfare. In both instances, drivers are first required to make a rightturn and then make a U-turn around a broad median. While this may seemtime-consuming, the study shows that it actually results in a significant timesavings since drivers are not stuck waiting to make left-hand turns or fortraffic from cross-streets to go across the thoroughfare.

* a 20 percent overall reduction in travel time compared to similar intersections thatuse conventional traffic designs

* superstreet intersections experience an average of 46 percent fewer reported automobile collisions – and 63 percent fewer collisionsthat result in personal injury

US motor vehicle deaths by year

2005   43,443  
2006   42,642 
2007   41,059
2008   37,261 
2009   33,808  

About 90-115 people die every day in vehicle crashes in the United States

Worldwide an estimated 1.2 million people are killed in roadcrashes each year and as many as 50 million are injured. Projectionsindicate that these figures will increase by about 65% over the next 20 yearsunless there is new commitment to prevention.

There is the potential that widespread superstreet adoption would save severalthousand lives per year in the USA and a few hundred thousand lives worldwide.

The paper is called Operational Effects of Signalized Superstreets in North Carolina.

Mythbusters showed that only using right turns saves gas
The myth was setup from the perspective of a delivery truck driver.Several locations within the San Francisco area were setup as delivery points, then tworoutes were derived. The first route was a more “logical” route trying not tofavor right turns. This route had eight left turns, four right turns, and atotal distance of 5.2 miles. The second route tried to exclude as many leftturns as practical. The “right turn” route was 6.8 miles long, had one leftturn and twenty-three right turns. Each route visited each stop in the sameorder.

The MythBusters concluded that right turns were indeed more efficient in theirtest. While the route favoring right turns was a longer distance and took alonger amount of time, it used only 4.0 gallons of fuel compared to 6.8 gallonsof fuel on the “control” route.

No Left Turn: ‘Superstreet’ Traffic Design Improves Travel Time, Safety

Release Date: 01.10.2011

Filed under Releases

The so-called “superstreet” traffic design results in significantlyfaster travel times, and leads to a drastic reduction in automobile collisionsand injuries, according to North Carolina State University researchers who haveconducted the largest-ever study of superstreets and their impacts.

Superstreets are surface roads, not freeways.  It is defined as athoroughfare where the left-hand turns from side streets are re-routed, as istraffic from side streets that needs to cross the thoroughfare. In bothinstances, drivers are first required to make a right turn and then make a U-turnaround a broad median. While this may seem time-consuming, the study shows thatit actually results in a significant time savings since drivers are not stuckwaiting to make left-hand turns or for traffic from cross-streets to go acrossthe thoroughfare.

"Superstreet" traffic designs result in faster travel timesand significantly fewer accidents, according to the new study.
“The study shows a 20 percent overall reduction in travel time comparedto similar intersections that use conventional traffic designs,” says Dr. JoeHummer, professor of civil, construction and environmental engineering at NCState and one of the researchers who conducted the study. “We also found thatsuperstreet intersections experience an average of 46 percent fewer reportedautomobile collisions – and 63 percent fewer collisions that result in personalinjury.”

The researchers assessed travel time at superstreet intersections asthe amount of time it takes a vehicle to pass through an intersection from themoment it reaches the intersection – whether traveling left, right or straightahead. The travel-time data were collected from three superstreets located ineastern and central North Carolina,all of which have traffic signals. The superstreet collision data werecollected from 13 superstreets located across North Carolina, none of which have trafficsignals.

The superstreet concept has been around for over 20 years, but littleresearch had been done to assess its effectiveness under real-world conditions.The NC State study is the largest analysis ever performed of the impact ofsuperstreets in real traffic conditions.

A paper on the travel time research is being presented Jan. 24 at theTransportation Research Board Annual Meeting in Washington, D.C.The paper is co-authored by Hummer, former NC State graduate students RebeccaHaley and Sarah Ott, and three researchers from NC State’s Institute forTransportation Research and Education: Robert Foyle, associate director;Christopher Cunningham, senior research associate; and Bastian Schroeder,research associate.

The collision research was part of an overarching report of the studysubmitted to the North Carolina Department of Transportation (NCDOT) lastmonth, and is the subject of a forthcoming paper. The study was funded byNCDOT.

NC State’s Department of Civil, Construction and EnvironmentalEngineering is part of the university’s College of Engineering.

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