the iteris vantage vector solution to eliminate the ......a way to reduce rear end collisions is to...

The Iteris Vantage Vector® Solution to Eliminate the Dilemma Zone

White Paper

July 2016

Innovating Through Informatics™

White Paper: The Iteris Vantage Vector® Solution to Eliminate the Dilemma Zone

Background: The reason for traffic signals.Traffic signals are warranted for two basic reasons: First, efficiency. Traffic signal warrants mainly deal with traffic volume and this justification is purely about effectively moving vehicles. The second area of warrants has to do with safety. Its basis is how to reduce the number of right angle accidents. The problem is that while traffic signals reduce right angle accidents, they can actually increase the number of rear end accidents due to the phenomena of the dilemma zone.

The Dilemma: Should I stop or should I go?All drivers approaching a signalized intersection have at some time or other no doubt experienced that “should I stop or should I go?” feeling when the traffic signal changes from GREEN to YELLOW. The usual, panicked thought is “Oh no! I’m too close to stop without slamming on my brakes, but I don’t think I can get to at least the middle of the intersection before the light turns red.” This leads to some short period of indecision, during which your car keeps on going. When the decision is finally made (to stop or to go), you soon find out if you have chosen incorrectly. You have just experienced a Dilemma Zone. A way to reduce rear end collisions is to make sure that the green is not terminated when vehicles are in the dilemma zone.

There are actually two distinct types of dilemma zones that can be present on an approach to a signalized intersection. The first is a “physical” dilemma zone. When a vehicle is so close to the intersection that even a rapid deceleration

(something a little less than a ‘jamb on the brakes’ panic-stop skid) won’t stop the vehicle before the light changes from yellow to red, then that driver obviously makes the “go for it” decision. With the recommended YELLOW change interval, there are distances from the intersection where the driver cannot proceed and legally make it through the signal. For those drivers traveling at or below the speed limit, the physical dilemma zone is created solely by signal timing.

The second, and far more notorious, is a “decision-making” dilemma zone. In this case, a driver will have enough time to reach the intersection if the choice is to “go for it”. However, they also have sufficient distance to commence a rapid deceleration and stop before reaching the intersection. Therefore, this type of dilemma zone starts at that critical ‘rapid-deceleration-is achievable’ point, and stretches back some variable distance. That zone’s size is variable based on both the driver’s speed and the driver’s aggressive-versus-passive demeanor. It extends back from that critical point to another point where the “normal” driver will always choose not to “go for it”. It is precisely because of the range in drivers’ demeanors that an aggressive driver following a passive driver is a recipe for a rear-end crash. The solution to this dilemma zone is also in the controller timing, but in this case the accurate detection of the vehicles’ presence while in the decision-making dilemma zone is critical. If so, then extending that movement’s GREEN interval until the lead vehicle passes the critical ‘rapid-deceleration-is-achievable’ point is the necessary solution.


Historical Solutions: Loop BasedMany years of study, innovation and traffic engineering problem-solving effort have led to a steady progression of increasingly effective loop detector treatments that to deal with dilemma zones. The first solution was putting a loop detector at the back (far) end of the dilemma zone.

The controller’s gap (or extension) time for that movement was set long enough to get that car to the critical point, as mentioned above. This gap time was calculated based on the 10th percentile of the traffic stream’s speed continuum; only 1 vehicle in 10 would be going slower than that.

Figure 1 depicts this single-detector solution. The significant problem with this solution was that, although it did eliminate dilemma zones, it also set such a long extension time that the controller didn’t gap out when traffic flows were light, and should have done so. Extending GREEN times means that other movements’ red times were lengthened objectionably, creating excessive motorist delay at the signalized intersection. This single-detector solution also took care of only the worst case condition, that being the almost slowest car. Faster vehicles (expected on 9 cycles out of 10) were given much longer gap times than they required to exit the dilemma zone.

Figure 1: Traditional Single Point Detection for High Speed Approaches

The more recent and widely used treatment for dilemma zones is to use a series of loops, set at specific distances from the stop bar and specific spacing between detectors. The layout selected for a particular approach was again based on speed, but instead of the 10th percentile speed, the 90th percentile speed vehicle is used. This multiple loop deployment utilized a much shorter extension time. Drivers traveling at a particular speed would be able to cover the distance between detectors, and reset the controller’s gap timer, if they were located within “their” dilemma zone. This layout greatly improved the intersection efficiency, by allowing the controller to gap out much more easily when cars were approaching slower than the 90th percentile, but had some inherent issues with existing technology.


Figure 2: Loop Based Multipoint Dilemma Zone Detection

Figure 2 shows the layout choices for a multi-loop detector scheme, and the required extension time set to get 90th percentile speed car from each loop detector to the end of the dilemma zone.

Iteris Solution: Vantage Vector Hybrid SensorThe basic problem with all of the loop-based solutions is that the design, layout and/or extension timing was based on a single “special” vehicle’s speed. No matter how fine-tuned the multi-loop system was, it would always miss serving the needs of a small proportion of the traffic stream. What is needed to overcome this limitation is to be able to track each vehicle individually, and create a timing strategy that would move them through their own, “personal” dilemma zone before the traffic signal turns from GREEN to YELLOW. Advanced technology in the Intelligent Transportation Systems sector has finally delivered on this new, “personalized” mitigation strategy.

The two main problems with this solution were:

1. Picking the right layout meant picking the “right” speed. If the design engineer’s estimate of the 90th percentile speed was even five mph off, the layout might not eliminate the dilemma zone for a large enough proportion of the traffic stream. If the wrong speed was chosen, it is unlikely that the multiple loops would ever be reconstructed in the “correct” locations.

2. The cost of detection dramatically increased with the deployment and maintenance of the multiple loop detectors. Additionally, the controller cabinet became filled with detector channels. More devices to purchase also meant more infrastructure components to maintain and eventually replace.


Iteris Video & Radar Fusion Detection SystemThe Vector sensor is built around both a video detection camera for stop bar detection and a radar unit for advanced detection to detect approaching vehicles at over 500 feet from the sensor. Utilizing the advanced algorithms in the radar unit, the Vector tracks all approaching vehicles, providing extremely accurate range and speed data of each individual vehicle. As the vehicles pass through up to five user-configured areas-of-interest, or trip lines, the system provides enhanced precision throughout the radar unit’s detection area. Vehicles then enter the detection area of the video camera as they reach the stop bar, thus the Vector provides total coverage for all vehicles approaching the intersection.

The Vector provides the user with the ability to configure five trip lines within the radar detection zone at a specific distance from the stop bar, a minimum and maximum speed threshold, and a defined trip line width. Figure 3 on the following page, shows this in more detail.

As a vehicle enters each of the trip line areas, the Vector determines if that vehicle is within the configured speed threshold. If it is, then the vehicle is most likely within the dilemma zone criteria, and an output is sent to the controller with the required extension timing for that vehicle to reach the next trip line area. This continues through each trip line until the vehicle has slowed down and hasn’t reached the next trip line in the required time before the extension has run out, or the vehicle has gone fast enough to have made it through the yellow light before it turned red.

Figure 3 shows these extension time events as the red areas between the “zones”.

Combined with the video detection area at the stop bar, the use of the trip lines within the Vector allows the user to create total dilemma zone coverage to ensure that high speed vehicles are detected, and the proper outputs are sent to the controller, so that vehicles can get through the yellow light safely, or are ensured to stop in enough time.

Applications with VectorIn addition to Dilemma Zone crash reduction, the Vector sensor provides many other applications that are extremely useful for today’s traffic engineering community:

• Collision Avoidance• Adaptive System Functionality• Bicycle Detection and Differentiation• Turning Movement Counts• Advance Data Collection


Figure 3: Vector Trip Line Example

1. Collision Avoidance with Siemens Red Protect Function Vector can be configured to provide an output to specific input of a Siemens traffic controller to delay the start of the green on the following phase if a vehicle is intelligently detected and predicted to run the red light. The Vector is ideally suited to deliver this intelligent detection by utilizing the radar component of the Vector, and its ability to very accurately detect the speed and distance of the vehicle approaching the intersection. Figure 4 on the following page shows a diagram of this.

2. Adaptive System Functionality Many adaptive control systems require the use of advance detection zones in conjunction with stop bar presence zones to provide proper functionality for the adaptive system to work effectively. An agency can save a significant amount of up-front installation cost and on-going maintenance costs by utilizing the Vector as a single-sensor for both detection functions.

Additionally, there are a number of adaptive control systems on the market today that can benefit from a sensor that can count the number of vehicles approaching the stop bar.


Figure 4: Vantage Vector Tripline Mode - Red Protect

The Vector provides a grouping function that will output a call anytime the total number of vehicles detected by the radar meets the programmed threshold. An example of this would be when using an Adaptive System and 8 vehicles are arriving on the minor street and you do not want them to be counted or to place a call in the advance area you would set this value to 9.

3. Bicycle Detection and DifferentiationAs with all Iteris video cameras, there are algorithms embedded in the software to accurately detect, and differentiate, bicycles approaching the stop bar. The Vector has this functionality embedded within the processor, and allows agencies to perform this detection simultaneously with vehicles. By providing the ability to differentiate bicycles, agencies can program the signal timing for accommodation of the slower moving bicycles to get through the intersection before the phase changes, ensuring a safer passage.


4. Turning Movement CountsProviding the ability to count vehicles moving through the intersection has long been a standard feature on all Iteris video cameras. This “free” counting feature gives a traffic engineer very accurate counts of all turning movements throughout the intersection in a very easy-to-use interface. By including this feature with Vector and all Iteris camera systems, the agency can save a significant amount of money by not having to perform manual counts, and the data can be utilized by the planning department for all intersections utilizing video detection.

5. Advance Data CollectionIn many cases, advanced detection systems are used to extend the through movement’s green phase. These advanced detector sensors can have placements of 50 to 350 feet from the stop bar. The Vector sensor

can supply these advance zones without the need for additional sensors, saving the agency substantial costs by not having to install or maintain additional sensors. Additionally, advanced detection also incorporates system detectors and speed detectors. The radar sensor within Vector provides high accuracy speed detection over other traditional detectors on the market today.

SummaryThe Vector Hybrid Sensor from Iteris is truly a one-of-a-kind product that can perform many simultaneous applications that improve intersection safety, reduce cost, and provide additional engineering features that can be utilized for enhancing intersection efficiency. Please visit www.iteris.com for more information on Vantage Vector and the complete line of Iteris detection systems.

the iteris vantage vector solution to eliminate the ......a way to reduce rear end collisions is to...

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