Rebecca Lynn Haley, author of the study, defines the concept:
"Superstreets, also known as the restricted crossing u-turn (RCUT) by the Federal Highway Administration (FHWA), works by redirecting the side street left turn and through movements to a downstream, one-way median opening. Left turns from the major road can be accommodated by a u-turn maneuver after the intersection or by a left turn crossover at the main intersection."
Randal O'Toole concludes, from reading the report, that "...this greatly reduces both the time required for traffic signals to cycle and the number of conflict points between the two streets."
Diagrams of the traffic flow are available at The Antiplanner.
Comments
Context matters
Superstreets improve flow for through traffic in motor vehicles, and so are best restricted to places where that is the only transportation function needed.
Jersey's experience with a superstreet isn't so great
I wonder if the authors of the study looked at Route 22 in Union County, New Jersey. It follows the design provided in the illustration, and it flows at parking lot speeds during the am and pm peak hours.
One of the aggravating factors is that there is dense commercial activity on either side of Route 22 and in the median. Theoretically, the design would move traffic well. But in practice, if there is enough traffic volume to consider a superstreet solution, there is probably going to be a strong demand for commercial activity along these roads. In most cities, especially in this economic climate, elected officials would be unlikely to leave developable land to lie fallow. The added density (and increased number of ingresses) would reduce the traffic flow benefits.
So you would have Route 22 in Union County, a superstreet that everybody hates to drive on, but feels they have to for the shopping.
Leonardo Vazquez, AICP/PP
Director, Professional Development Institute and The Leading Institute
Program Director for Professional and Executive Education
Edward J. Bloustein School of Planning and Public Policy
Rutgers, The State University of New Je
Randal should move to the Middle East
These superstreets abound in the region and are an abomination from both a planning and environmental standpoint.
In theory traffic should flow better, but like most supersized roadways, induced demand just rears it's ugly head and you end up with increased traffic loads that can't be handled by any amount of left turn crossovers.
Mr. O'Toole should spend a little time in Riyadh, Saudi Arabia to see just how poorly the system works during rush hour, and how incredibly soul deadening streets like these can make a city. In fact, we should take up a donation to move Randal to Riyadh on a full time basis, as it is just the kind of car dependent 'utopia' we would have if the Antiplanner had his druthers.
Secondly, the amount of wasted gas spent driving to the next major intersection (which in the case of Riyadh is usually closer to a 1/2 mile) cannot be ignored. Granted, idling at the left hand turn light can also be wasteful, but it beats the mile or so spent driving at highway speeds (or stuck in traffic) to the u-turn of crossover.