System Requirements - MnDOT

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System Requirementsprepared forMinnesota Department of Transportation(MnDOT)forRural Intersection Conflict Warning Systems IIDeploymentFebruary 2, 2015

AcknowledgementsThese system requirements were originally developed by MnDOT for the statewide Rural IntersectionConflict Warning System (RICWS) project in October 2012. Carver County asked SRF Consulting Group torevise this document to incorporate lessons learned from the RICWS project to enable the installation ofadditional Intersection Conflict Warning Systems (ICWS) on T.H. 212 in Carver County. MnDOTparticipated in the development of this project and the associated systems engineering documents.These systems requirements were then revised by SRF Consulting Group for use on MnDOT’s seconddeployment Rural Intersections Conflict Warning Systems II (RICWS II).IntroductionThe primary goal of an ICWS system is to reduce right angle crashes at a stop-controlled intersection.These systems address crashes at stop-controlled intersections by providing drivers with a dynamicwarning of other vehicles approaching or entering the intersection. ICWS typically consist of staticsigning, detection and dynamic elements as illustrated in Figure 1.Figure 1 Intersection Conflict Warning System ConceptAs they are currently conceived, ICWS fit within Minnesota’s ITS architecture under the AdvancedVehicle Safety Systems market packages AVSS05-Intersection Safety Warning and AVSS10-IntersectionCollision Avoidance.February 2, 2015Page 1

This document presents detailed system requirements for ICWS systems. These requirements are basedon MnDOT experience to-date with ICWS and they will evolve as more is learned.DefinitionsIntersection – as defined in the MUTCD, Part 1. General, Section 1A.13 Definitions of Headings, Words,and Phrases in this Manual:a) The area embraced within the prolongation or connection of the lateral curb lines, or if not, thelateral boundary lines of the roadways of two highways that join one another at, orapproximately at, right angles or the area within which vehicles traveling on different highwaysthat join at any other angle might come into conflict.b) The junction of an alley or driveway with a roadway or highway shall not constitute anintersection, unless the roadway or highway at said junction is controlled by a traffic controldevice.c) If a highway includes two roadways that are 30 feet or more apart (see definition of median),then every crossing of each roadway of such divided highway by an intersection highway shallbe a separate intersection.d) If both intersecting highways include two roadways that are 30 feet or more apart, then everycrossing of any two roadways of such highway shall be a separate intersection.Approaching Vehicle – a motor vehicle that is approaching the intersection which is on:a) The minor road and at some point was more than time “t” from the intersection.b) The major road and at some point was more than the major road lag time from the intersection.Entering Vehicle – a motor vehicle that turns onto the minor road less than the time “t” from theintersection or a motor vehicle that enters the major road less than the major road lag time from theintersection.Operational Malfunction – component failures and malfunctions of otherwise functional hardware andsoftware that prevents the RICWS system from displaying alerts to any approaching vehicle withinparameters defined in these system requirements.System Availability – is the design life of the system divided by the design life plus the average repairtime per year (Design Life/(Design Life (Repair Time*Average Failures per Year). See Appendix B forsystem availability discussion.System Repair Time – is defined as a 72 hour allowable window for response to a reported operationalmalfunction.February 2, 2015Page 2

Time “t” – a single constant for the intersection and is the largest time computed based on the majorroad vehicle lag time from 2.5 seconds in advance of the major road warning sign to the intersection atthe posted speed limit.User – Refers to Contractor or Agency field personnel on site.User-configurable - is the parameter that allows engineering judgment of how best to establishdetection and alert activation parameters based on traffic characteristics (gap selection, sight distance,and speed of each approaching vehicle) at a given intersection.Vehicles – For the purpose of these requirements the term vehicles shall mean motor vehicles asdefined in Minnesota Statutes and the Minnesota Manual on Uniform Traffic Control Devices.Major Road Lag time - the portion of the gap which remains from the major road vehicle to the minorroad vehicle at the stop line. This is further defined in NCHRP Report 383, Intersection Sight Distance.February 2, 2015Page 3

System RequirementsSystem requirements are verifiable details that define what the intersection conflict warning system will do. They address either functional orperformance/operational aspects of the system and are noted as such in the following table. Each of the high level requirements below wasoriginally translated from stakeholder needs identified in the project Concept of Operations. The number references allow for traceability backto those needs and forward to the detailed system requirements. The first number refers to one of three stakeholder need categories – DriverAlerts, Traffic Control or Assessment and Evaluation. The second number refers to the stakeholder needs as they were presented in the Conceptof Operations. The third number is used to track high level requirements and the final reference number relates to detailed systemrequirements, where applicable. Some reference numbers may also be out of sequence because the stakeholder needs that originally promptedthem were performance or operationally oriented and therefore more appropriately addressed in project contract documents rather thanfunctional requirements.NumberHigh Level Requirements11.1.1Driver AlertsICWS shall detect vehicles approaching and waitingat the stop or yield signs on the minor road.Number1. shall display alerts to major road driverswhenever a vehicle is approaching or waiting at thestop or yield sign on the minor road. 2, 2015Detailed System RequirementsICWS shall detect approaching vehicles from both directions on theminor road as they are approaching the intersection less than time t,from the intersection.ICWS shall detect any vehicle on the minor road that is waiting at thestop or yield sign on the minor road.ICWS shall be capable of detecting all entering vehicles on the minorroad as they turn onto the minor road. Design considerations forincluding this detection at specific sites are included in the attachedDesign Guidelines.ICWS alert shall be active on the major road whenever anyapproaching vehicle on the minor road is less than time “t” awayfrom the stop sign.ICWS alert shall be active on the major road whenever any vehicleon the minor road is waiting at the stop or yield sign.Page 4

NumberHigh Level RequirementsNumber1.1.2.3ICWS alert shall be active on the major road whenever any vehiclefrom the minor road is within the intersection. alert shall be active on the major road whenever any vehicleon the minor road is waiting at the median yield sign.ICWS alert shall be inactive on the major road whenever: there are no approaching vehicles on the minor road lessthan time “t” away from the intersection; there are no vehicles waiting at the stop sign; there are no minor road vehicles within the intersection; and there are no vehicles waiting at the median yield sign.System activation and de-activation based on time “t” shall be within 0.5 seconds of time “t”.ICWS shall respond with at least 99.95% accuracy for major roadalerts.No further detail required. may display an alert for major road driverseven if no major road vehicles are present.ICWS alerts shall be visible to major road drivers ata distance that allows them to take correctiveaction.ICWS shall detect all vehicles as they approach theintersection on the major road.February 2, 2015Detailed System Requirements1.2.1.1ICWS alerts shall be visible from any approach lanes on the majorroad. alerts shall be placed on the major road according to MNMUTCD Part 2C. Warning Signs and Object Markers, Section 2C.05Placement of Warning Signs, and using Table 2C-4. Guidelines forAdvance Placement of Warning Signs.ICWS shall detect any approaching vehicle from both directions, inall lanes, as they are approaching the intersection within a userconfigurable lag time on the major road. 5

NumberHigh Level RequirementsNumber1. shall display alerts to minor road driverswhenever vehicles approach the intersection on themajor .2.6February 2, 2015Detailed System RequirementsICWS shall be capable of detecting all entering vehicles on the majorroad as they enter the major road. Design considerations forincluding this detection at specific sites are included in the attachedDesign Guidelines.ICWS alert shall be active on the minor road whenever anyapproaching vehicle on the major road is less than a userconfigurable lag time away from the intersection.ICWS alert shall be active on the minor road whenever any majorroad approaching vehicle is within the intersection.ICWS alert shall be inactive on the minor road whenever there areno approaching vehicles less than a user-configurable lag time awayfrom the intersection on the major road.ICWS alert shall allow a user-configurable lag time between 4 and7.5 seconds, in increments of 0.1 seconds, for any approachingvehicle on the major road. The lag time will define active/inactiveparameters for the minor road alert.ICWS alert lag-time shall allow for user configuration of lag time onthe major road by changing parameters within the system softwareand without changes to detector placement, hardware, orfirmware/software programingICWS shall meet requirements for user-configurable active andinactive lag timing whenever any approaching vehicle speed iswithin 12 MPH of the posted speed on the major road; excludingvehicles that may be decelerating to execute a turn at theintersection.System activation and de-activation based on user configurable lagtime shall be within /- 0.5 seconds of the lag time the user hasconfigured.Page 6

Number1. Level RequirementsICWS may display an alert for minor road driverseven if no minor road vehicles are present.ICWS shall display alerts at a location visible tominor road drivers waiting at the stop sign.ICWS design shall include dynamic alerts.To the extent possible, ICWS shall followrecommended design practices described in “Designand Evaluation Guidance for Intersection ConflictWarning Systems” authored by the ENTERPRISETransportation Pooled Fund program.ICWS shall have similar placement, signcombinations and message sets at each deploymentsite in Minnesota.Number1.3.1.2ICWS shall respond with at least 99.95% accuracy for minor roadalerts.No further detail required. alert shall be placed on far right corner of intersection, acrossfrom the stop sign, where intersection geometry permits. For thoseintersections with restricted geometry, ICWS alert may be placed onfar left corner of intersection, across from the stop sign.No further detail required.ICWS shall be designed using the placement, sign combinations andmessage sets described for Major and Minor Road Alert for 2Lane/2-Lane (or Multi-Lane) Intersection or for a major road alertonly. alerts shall be conspicuous.February 2, 2015Detailed System Requirements1.8.1.1ICWS alert shall use TRAFFIC APPROACHING WHEN FLASHING (W3X8b) sign(s) on the minor roadway. The ICWS alert shall use eitherENTERING TRAFFIC WHEN FLASHING (W3-X8a and W3-X8aP) ontwo-lane two-way major roadway or ENTERING TRAFFIC WHENFLASHING (W3-X8) on multi-lane divided major roadway.The TRAFFIC APPROACHING WHEN FLASHING (W3-X8b) sign(s) onthe minor roadway shall be a blank out sign allowing the sign to bede-energized by the control system or user. This allows amalfunctioning system to appear different than an inactive system.ICWS alert shall conform to MN MUTCD 2A.7 Retroreflectivity andIllumination, MN MUTCD 2L.4 Design Characteristics of ChangeableMessage Signs, and TEM 6-4.05.05 Retroreflective Sheeting Policyfor sign sheeting materials and LED brightness.Page 7

Number22. Level RequirementsNumberDetailed System RequirementsTraffic ControlICWS shall function as a warning sign as defined inMN MUTCD 2C.1-2C.2.ICWS shall operate continuously 24x7, 365 days peryear, with minimal service interruption.No further detail 2, 2015The system shall operate continuously 24 hours per day, 365 daysper year during its design life of 10 years (87,600 hours) without theneed for restarts, re-initializations for other external interventions.The system shall have availability over its design life greater than99.9% as defined in these requirements.ICWS components shall conform to NEMA TS 2-2003 environmentalrequirements.ICWS alert shall conform to NEMA TS 4-2005 standards for thehardware and functional characteristics of electronically controlleddynamic message signs, if used.ICWS shall be connected to utility power service.ICWS shall detect any detection component malfunction.ICWS system communication components shall comply with FCCemission requirements. The system shall be able to meet neededFCC approvals when design is complete.ICWS Control Cabinet shall meet the requirements of UL 508“Standard for Industrial Control Equipment”, January 28th 1999Edition, and the requirements of the current edition of the NationalElectrical Code by either being listed by a Nationally RecognizedTesting