Is your city growing faster than your roads can sustain? Does your city have a busy intersection that backs up for blocks waiting for drivers wanting to take left turns?
Often, when an area grows faster than the roadways can support, intersections get backed up with drivers making left-hand turns filling up the turn lane and spilling out into through traffic. Drivers turning left have to wait for oncoming traffic. Drivers behind the queue of turning vehicles have to wait for it to clear before going through the intersection. This frequently happens around shopping center developments or businesses. In busy areas, this can create long backups and driver frustration.
In these situations, cities will often need to invest in updating the interchanges, which can be costly and take a long time to complete.
The continuous flow intersection (CFI), also called a cross-over displaced left turn (XDL or DLT intersection) is an intersection design that solves these issues with a unique, efficient design. It eliminates the congestion caused by drivers making left turns.
“The idea is to have left-turning drivers start their turn at a signal controlled intersection several hundred feet before the intersection,” says Paul Wells, SEH highway designer. “This allows left-turn movements to proceed simultaneously with the through traffic. People wanting to continue forward can stay in motion, instead of being stuck behind someone who can’t get through an intersection.”
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With this type of interchange, a single traffic signal that normally alternates between eight different movements at the intersection is replaced by three signals that only control two separate movements at each signal. There is the potential to stop three times: once at a midblock signal as you approach the intersection, once at the intersection and once at a midblock signal after leaving the intersection. However, with careful signal coordination, traffic can keep flowing significantly more efficiently, safely and smoothly without those potential stops.
“The reason congestion is growing at the Havana/Easter intersection in Centennial is twofold. First, the adjacent undeveloped land is filling in with commercial and office developments, and second, the major parallel roadway in the vicinity is over capacity and vehicles are diverting their routes through the Havana Street/Easter Avenue intersection,” said Jon Larson, SEH traffic engineer. “SEH performed a traffic study and came up with some different intersection options for the City to consider.”
Centennial ultimately chose the CFI to help alleviate the congestion and keep traffic flowing smoothly.
The design includes modifying the current four-way intersection into a three-way intersection, something Larson says will also cut down on congestion in the area.
The City of Centennial expects to bring the project to construction within the next five years, giving residents some much-needed relief to the congestion in the area.
“It’s been great being part of this process,” says Larson. “Even a few minutes less spent in traffic means even more time to spend with your family.”
Jon Larson, PE*, PTOE, is a traffic engineer and family man dedicated to helping cities solve traffic congestion problems. Contact Jon
Paul Wells, PE*, is a senior highway designer and champion of Colorado roadway solutions. Contact Paul
*Registered Professional Engineer in CO
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