Frequently Asked Questions regarding CFI
Continuous Flow Intersections
Continuous Flow Intersections are a new style of intersection, developed in Mexico. In the U.S., CFIs have been implemented in Louisiana, Maryland, Utah, Missouri, and New York.
What is a CFI?
How is this better than a traditional intersection?
How does this look and work?
Why does a CFI work better at Randall and
Algonquin?
There are a large number of signalized intersections
associated with this design, what happens if power goes out at this intersection?
Who do I contact for more information?
What is a CFI?
A continuous flow intersection has traffic turning left placed to the
left of oncoming traffic, opposite where it is normally. This removes
the conflict between on-coming traffic and traffic turning left. Vehicles
turning left access the lane a few hundred feet in front of the intersection.
How is this better than a traditional intersection?
Since left-turning traffic doesn't have to cross on-coming traffic, using
this type of intersection will increase the amount of "green" time
on the main-line route. At the intersection at Baton Rouge, Louisiana,
wait time was reduced from four minutes to less than a minute. This
type of intersection provides a comparable level of vehicle flow as
that on an interstate at a fraction of the cost, and is a dramatic
improvement over conventional intersections.
How does this look and work?
The attached animations should give a general idea of the difference
between a traditional and continuous flow intersection, as well as
how vehicles making left turns would travel:
- Traditional intersection (24.5 Mb)
- Continuous flow intersection (21.2 Mb)
- Making a left at a CFI (14.1 Mb)
Why does a CFI work better at Randall and Algonquin?
Under No Action conditions, the intersection of Randall Road and Algonquin
Road does not accommodate the projected 2030 peak hour volumes and
results in a failing level of service (LOS). Average delay at the intersection
would be almost eight minutes per vehicle. As a result, a conventional
signalized intersection (with dual-left turns) and a continuous flow
intersection were studied for their ability to accommodate the projected
2030 peak hour volumes. Both types of intersection configurations studied
(continuous flow, conventional intersection) will provide the necessary
capacity to accommodate the projected 2030 peak hour volumes. However,
the dual left-turn lane concept would operate at LOS F during peak
hours and vehicles would experience average delay of almost two minutes
(93 seconds), whereas the continuous flow intersection concept would
operate at LOS D during these hours and vehicles would experience less
than one minute of delay (36 seconds). Therefore, the latter configuration
would accommodate greater thru traffic volumes along Randall Road in
the future.
Since the Randall Road and Algonquin Road Intersection is a major intersection along the Randall Road corridor, it is important to ensure that the improvements at this intersection improve operations of the intersection and throughout the transportation network. Under No Action conditions, the total network delay along Randall Road between County Line Road and Ackman Road is over 16 minutes per vehicle. That means that the average driver will be delayed for 16 minutes while traveling from one end of the corridor to the other. In comparison, the conventional signalized intersection reduces this delay to approximately 3.4 minutes per vehicle and the continuous flow intersection reduces this delay to as little as 2.4 minutes per vehicle.
The implementation of a continuous flow intersection at the intersection of Randall Road and Algonquin Road results in operational improvements to the intersection as well as relief to the entire network from County Line Road to Ackman Road. The continuous flow intersection operates with less delay and shorter queue lengths than a conventional signalized intersection. Reduced vehicular delay is associated with reduced fuel consumption and fewer vehicle emissions. In addition, there are fewer conflict points with a continuous flow intersection than a conventional signal and the conflict between left-turning vehicles and oncoming traffic at the main intersection.
There are a large number of signalized intersections associated
with this design, what happens if power goes out at this intersection?
There are a large number of signals proposed with a CFI in addition to
several conflicting routes; any loss of electrical power has the potential
to cause serious problems at the intersection. A backup system will be
introduced at the intersection such as a generator or battery-powered
light emitting diode heads.
Who do I contact for more information?
For questions related to the information presented, contact the McHenry
County Division of Transportation:
Wally Dittrich
McHenry County Division of Transportation
16111 Nelson Road
Woodstock, IL 60098
Phone: 815.334.4980
Fax: 815.334.4989.