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Publication Number:  FHWA-HRT-16-035    Date:  June 2016
Publication Number: FHWA-HRT-16-035
Date: June 2016

 

Safety Evaluation of Intersection Conflict Warning Systems

Appendix B: Additional Installation Details

The following appendix presents additional details provided by Minnesota, Missouri, and North Carolina. States were asked to provide responses to the following questions:

  1. How were treatment signs, messages, and approaches selected for treatment? For example, how were sites selected to have treatment on the major or minor approaches only, or how were sites selected to be treated on BOTH the major and minor routes?

  2. How were signs and messages selected (e.g., visual display versus message, “When Flashing” versus no message, or overhead versus post-mounted)?

  3. Do you know if other geometric changes or countermeasures (e.g., addition of turn lanes) were implemented concurrently with the ICWS?

  4. We would like to provide a summary of the ICWS characteristics below. Do you have any standard drawings that applied to the treatment sites considered by the study?

    1. Location of sign on major approach and/or minor approaches.

    2. Location/type of detection on major and/or minor approaches.

    3. Messages on the signs.

    4. Sign size.

    5. Detector timing parameters.

  5. Was crash history the major criteria for site selection? Were any specific crash types targeted? Please specify any criteria.

  6. Were there any requirements for ICWS implementation (e.g., minimum major/minor route volumes, minimum/maximum speed limits)?

  7. Please describe any notable challenges related to ICWS installation and how you overcame them.

  8. Please describe any notable challenges related to ICWS maintenance and how you overcame them.

  9. What lessons learned or recommendations would you share with another State interested in the application of ICWS?

  10. Can you provide any estimates on cost of ICWS operation and maintenance for intersections with installations only on minor approaches, only on major approaches, or on both the major and minor approaches? Are there any noted differences for overhead versus post-mounted installations?

Responses from Minnesota

Minnesota responded to all 10 questions. Their responses are listed in numeric order. The responses are listed separately for cooperative intersection collision avoidance system (CICAS) sites and for ICWS sites.

The following responses were received regarding CICAS installations:

  1. The locations for the CICAS system were selected based on their crash history.These were locations with a documented crash history of angle crashes at expressway intersections.Only the minor approach received treatment via the CMS that was installed at the intersection.A report describing the location selection and the preliminary candidate message types can be found at http://www.dot.state.mn.us/guidestar/ 2001_2005/ids/2007_33.pdf.

  2. Details on the various signs and messages where researched over a several year period.Details on these studies can be found at http://www.dot.state.mn.us/guidestar/ 2006_2010/cicas.html. Ultimately, the design that was implemented was informed by this research as well as feasibility aspects brought forward by the University.

  3. No additional geometric changes were incorporated into the deployment of the CICAS system.

  4. Additional details are discoverable but would require some effort (detector parameters, etc.) or may be included in reports published at the hyperlink in A2. See page 13/27 of the report found at http://www.dot.state.mn.us/guidestar/2001_2005/ids/2007_33.pdf.

  5. The TH 52/CSAH 9 intersection had a known crash history of high speed right-angle crashes and that brought the project to its location.While there was no specific site criteria that was used to identify site selection factors used for other locations the following factors were used to identify the other deployment sites:number and severity of right-angle crashes (looking for high frequency and high severity in terms of fatal and serious injury crashes) and expressway intersections with stop control. A report describing the location selection can be found at http://www.dot.state.mn.us/guidestar/ 2001_2005/ids/2007_33.pdf.

  6. No. There was concern about higher volume roads where the system would be frequently showing a no movement recommendation due to smaller gaps based on the traffic composition. This pushed the system out of “super” high volume expressways in urban areas to more rural environments where the demand was not as consistent throughout the day.

  7. The installation was fairly straight forward but there were some challenges with post design and guardrail requirements for the system. Engineering judgment was used to move forward with an acceptable layout.

  8. Since this system was a prototype keeping the system operational 24/7 was a challenge. This was confounded by having remote locations not near the university staff office facilities. Diagnostics could be done remotely to check system status but diagnosing repairs required a site visit and potentially ordering replacement parts. It should also be noted that the vendor for the signs at one of the locations went out of business, making it difficult to repair the signs and get parts. Also, electricity for the large DMS signs was very expensive.

  9. A plethora of information was used to develop and design this new elaborate system.Substantial information was gathered at the locations that provided details on drivers and their gap acceptance. In the end, drivers still made bad choices at intersections and crashes occurred even after the system was installed. Every crash that occurred after the system was installed had the correct message displayed, indicating that no movement was advised. A system with lower installation and maintenance cost would be more likely to be built.

  10. Due to the prototype nature of this project we are not able to provide any meaningful costs on the installation and operation of this system. The project costs were high due to the research and development that went into the system, the goal was that someone would commercialize the product with standard detection and logic in the future based on the results of this research.

The following responses were received regarding the ICWS installations:

  1. The locations for the [rural intersection conflict warning system] RICWS system were selected based on their crash history and local input into intersections to test this new technology—these locations in general were not considered black spots. The default system design was to employ warning signs for all approaches to the intersection

  2. The goal was to provide a system that leveraged off the shelf technology so the project looked to leverage existing signs (MUTCD compliant) and compliment them with technology to flash when conditions warranted.

  3. No additional geometric changes were incorporated into the deployment of the RICWS system.

  4. Attached are files that contain some of the information requested in the above bullets.

  5. The locations selected were based on a variety of factors including the perception of a crash problem (i.e., lots of near misses, less than standard site distance, limited crash history). Angle crashes were the focus of this intersection treatment.

  6. No.

  7. The installation was fairly straight forward but there were some challenges keeping the system operational 100% of the time.

  8. Since this system was a prototype keeping the system operational 24/7 was a challenge.This was confounded by not having an easy way to diagnose whether the system was operational or not.

  9. While this system is relatively simple to design and install substantial effort was focused on keeping the system operational throughout the deployment.A system with lower installation and maintenance cost would be more desirable in the future.

  10. Due to the prototype nature of this project we are not able to provide any meaningful costs on the installation and operation of this system. The project costs were high due to the research and development that went into the system, the goal was that someone would commercialize the product with standard detection and logic in the future based on the results of this research. A new system has been designed and deployed based on the lessons learned from this system, however the costs are well in excess of $50k per intersection.

Responses from Missouri

Missouri provided responses to four of the questions.

Response to question 2: For the message, we have a couple that have been used, but it seems like the “traffic approaching when flashing” is being taken out of service due to litigation concerns (may not always flash).

Response to question 5. These locations were driven by crash issues.

Response to question 9. If we see a continued trend in angle collisions after installation, we may decide to modify the access and potentially install a j-turn design (RCUT).

Response to question 10. I am confident we are hoping to get a 10 year plus lifespan out of the locations we have installed this countermeasure.

Responses from North Carolina

North Carolina responded to all 10 questions. Its responses are listed in numeric order. Figure 17 and Figure 18 provide the pre- and post-2012 crash reduction factors used by NCDOT. Figure 19 through figure 21 present example diagrams of ICWS applications in North Carolina.

  1. Treatment sites were selected by the local traffic engineering staff, for the most part based on an observed crash experience. The decision of where to place signs (overhead in the intersection or in advance of the intersection, an on which approaches) likely depended upon:

    1. Whether there was an existing standard overall flasher in the intersection.

      1. At some of the locations, a standard overhead flasher was already in place (likely as a safety treatment that hadn’t worked well). If there was an existing overhead flasher, the ICWS likely replaced the standard flasher in the same spot.

    2. Whether there were site distance issues at the intersection.

      1. In some cases, if the intersection was located in a curve, the flashers may be placed in advance of the intersection on the major road so that drivers could better see the warning.

    3. The personal preference of the local Division/Regional traffic engineers in the area where it was placed (this may be the biggest reasoning behind the design at each site).

  2. The decision on which messages to use also depended upon the preference of the local traffic engineering staff. Some feel more comfortable adding the “When Flashing” to the message than others due to potential/perceived liability issues.

  3. The ICWS should be the only change made to the sites during the study periods.

  4. See the attached drawings of the countermeasures for examples (Examples 1–3).[See figure 19 through figure 21.]

  5. Yes, most of the sites were selected based on an existing crash pattern. The number of total crashes in the before period at each site varies from 0 crashes to 9.5 crashes per year, with an average of 3.7 crashes per year at 74 sites. Note, there was only 1 site with 0 crashes in the before period. Target crashes were frontal impact, specifically angle crash types where a vehicle pulled out from the stop-controlled leg. The number of target crashes in the before period at each site varied from 0 crashes per year to 8.5 crashes per year, with an average of 3.0 crashes per year at 74 sites. Many of the sites were funded through the Spot Safety program, where they competed with other safety projects based on the B/C ratio, among other items. A site with a strong pattern of crashes, including some high severity crashes, may be more likely to be funded depending upon the total cost of the project.

  6. There were not volume or speed thresholds. Intersection AADTs ranged from approximately 3,000 to 30,000, with an average of 7,300 at 74 sites. Major road speed limits ranged from 35 to 55 mph, although a majority of sites were located on high-speed facilities.

  7. We have no notable challenges related to ICWS installation to report. We have been installing these countermeasures since 1997, so there may have been some installation issues to overcome initially, but we do not have a record of those items.

  8. We also do not have any notable challenges related to ICWS maintenance. We have been installing these countermeasures since 1997, so there may have been some maintenance issues to overcome initially, but we do not have a record of those items.

  9. In our experience, ICWS may work best when signs are posted on the major road in advance of the intersection. A combination of signs (i.e., minor road signs with major road signs in advance of the intersection) may be most effective. Also, ICWS appears to be more effective when the major road is a two-lane cross-section as opposed to a four-lane divided cross-section. Probably the biggest thing we learned was the crash reduction factor estimates we used for this type of project pre-2012 to post-2012 in our B/C process within our Spot Safety program. Since there was no good crash reduction factor research available prior to 2012, we decided to use a 25 percent reduction in total crashes for these types of countermeasures. After our evaluation of the sites we shared, we adjusted our crash reduction factor estimates to match the data results our analysis provided. Based on the new information, I believe there were a lot of sites we would have never installed this countermeasure; those with a low opportunity for same improvements (see values for Post-2012 below).

    Figure 17. Graphic. North Carolina pre-2012 crash reduction factor. This graphic shows that the expected percent reduction for the countermeasure “Upgrade Overhead Warning Flasher Actuated Vehicles Entering is 25 percent for total crashes.

    © NCDOT.

    Figure 17. Graphic. North Carolina pre-2012 crash reduction factor.

    Figure 18. Graphic. North Carolina post-2012 crash reduction factor. This graphic shows expected crash reductions for total crashes for differing countermeasures. For an actuated vehicle entering when flashing (two-lane at two-lane intersections), expect a 6-percent increase in total crashes for a site with overhead signs and flashers on the major road and a loop on the minor road; expect a 5 percent decrease in total crashes for a site with overhead signs and flashers on the minor road and a loop on the major road; expect a 32-percent reduction in total crashes for a site with post-mounted signs and flashers on the major road and a loop on the minor road; and expect a 25-percent reduction in total crashes for a site with a combination of signs and flashers on the major/minor roads and loops on major/minor roads. For four-lane at two-lane intersections, all potential countermeasure scenarios, expect a 7-percent increase in total crashes.

    © NCDOT.

    Figure 18. Graphic. North Carolina post-2012 crash reduction factor.



  10. We are currently using $500 for the annual maintenance costs and $125 for the annual utility costs in our B/C process within our Spot Safety program. We do not differentiate the costs between the following four categories:

    • Overhead signs and flashers on major, loop in minor.

    • Overhead signs and flashers on minor, loop on major.

    • Post mounted signs and flashers on major, loop on minor.

    • Combination of signs and flashers on major/minor, loops on major/minor.

Figure 19. Diagram. Example 1—overhead sign on major route. This diagram presents an example of the design of an intersection with an overhead sign on the major route.

© NCDOT.

Figure 19. Diagram. Example 1—overhead sign on major route.

Figure 20. Diagram. Example 2—overhead sign on minor route. This diagram presents an example of the design of an intersection with an overhead sign on the minor route.

© NCDOT.

Figure 20. Diagram. Example 2—overhead sign on minor route.

Figure 21. Diagram. Example 3—post-mounted sign on major route. This diagram presents an example of the design of an intersection with a post-mounted sign on the major approach.

© NCDOT.

Figure 21. Diagram. Example 3—post-mounted sign on major approach.

 

 

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