by Adolfo Pesquera
San Antonio (Bexar Co.) – It turns out you can’t see the bottleneck from space (we checked), but the Texas Department of Transportation claims to have solved the traffic jam at Bandera Road and West Loop 1604 North.
TxDOT and RPS Klotz Associates staff held a meet-and-greet with the public Thursday evening at O’Connor High School in Helotes to help decipher their drawings.
Their solution is based on something called the DLT (displaced left turn).
Without any claim as to who invented this design, here is an October 2009 definition from the Federal Highway Administration Research and Technology website:
The DLT interchange is a new interchange design that has similarities to both the at-grade DLT intersection and the double crossover diamond (DCD) interchange. The main feature of the DLT interchange is that left-turning traffic crosses over the opposing through lanes several hundred feet upstream of the main intersection and then proceeds on a new roadway situated between the opposing through lanes and a roadway that carries right-turning traffic from the ramp. From this new roadway, the left-turn traffic completes its maneuver onto the on-ramp.
A DLT interchange has four signalized junctions: two at the crossovers for the DLT movements and two at the ramp terminals of the interchange. The DLT interchange design reduces the number of phases at the signal-controlled ramp terminals within the interchange from three to two, thereby reducing delays to drivers, pedestrians, and bicyclists as they pass through the interchange area. To ensure the smooth progression of traffic, all four signalized junctions are operated in a coordinated system. A DLT interchange has the same number of conflict points as a conventional diamond interchange. However, fewer angle crashes may be anticipated in a DLT interchange compared with a conventional interchange because conflicts are more separated.
Was that helpful? No? Okay, let’s put it this way:
For those drivers that need to make a left turn at the intersection, two left turns are required instead of one. At the start of the first left turn, the motorist gets in a long line controlled by a traffic signal that, once passed, moves the motorist to the left of oncoming traffic–just like they drive in England (wrong.side.of.road).
The motorist is now in a second queue that can proceed unobstructed into the intersection and make the left turn without a second stop.
The displaced left turn design will be installed on Bandera Road, on both east and west approaches toward 1604. Construction is scheduled to begin in the fall of 2017 and end 12 months later. This is a $5.5 million project.
TxDOT predicts this fix will reduce vehicular delays caused by that intersection for 22 years (up until 2040).
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adolfo@virtualbx.com
