Mississippi DOT Smart Work Zone Systems Performance Measures

Editor's Notes

• #4 MDOT uses Smart Work Zone Systems to accomplish its missison statement of making the Highways safer for users.Improve safety, by reducing accidents. Alert drivers to slowing or stopped traffic, and clear accidents more quickly.Reduce congestion by monitoring travel times, alert drivers to delays before decision points so alternate routes are available.Evaluate for the future: demo products, gather and study traffic flow against base line traffic, virtual modeling future projects with previous SWZS traffic data, benefit cost analysis by assiging costs to delay safety vehicle operating costs, ect.
• #7 Fast tracked funding – interstate widening, split diamond interchange, head to head traffic flowContractor designed vsmdot designed (like a traffic control plan)Minimum details for this project due to fast tracked funding, mainly detailed in specifications and notice to bidders for a contractor designed systemBidding involved a lump sum bid item for the “SWZ system” that provides full payment for the SWZS. A per each pay item for additional field devices was included should the project engineer request them during construction. System monitoring is a lump sum bid item pay for on a daily basis for resetting devices, web services and ongoing maintenance
• #8 By addendum we were able to sneak a SWZS specification into the plans and a cooresponding notice to bidders for TMC modifications that sets up an RSS feed to the statewide MDOT TMC in Jackson.These are all portable trailer mounted, cell phone comm, solar powered devices. All data recorded will be provided in polling increments to the State Agency. A minimum of 10 PCMS boards were requested with 8 in the field, 2 for backup/spares. A minimum of 20 radar units were requested.Typical sign messages were given based on speed threasholds.
• #9 The contractor, Mississippi Based Hill Brothers Const. used ASTI as a sub contractor. The system they proposed to MDOT essentially spread the devices out farther both North and South of the work zone from around a 5 mile footprint discussed in the bid documents to a 13 miles footprint. They used 10 signs (5 north and 5 south) in the field as opposed to the 8 recommended and also used 20 data collectors. They did not place any devices within the 2 mile temporary head to head traffic arrangement.
• #10 ASTI Website developed Real-Time traffic countsDatabase for Speed, Volume OccupancyDatabase of PCMS MessagesASTI maintains the website icons and updates all information
• #11 Establishing and monitoring performance is a way of determining the usefulness of a system to the agency, to the contractor, and to the public travelling through the work zone. It is important for agencies to track performance measures in order to justify the additional cost to the project of utilizing ITS technologies as weighed against the benefits the system provides. Care should betaken to conduct any analysis in such a way that the affects can be attributed to the application being studied and not to any other measures. The specific measures tracked should be aligned with the goals of the particular application(s) used, but typically, metrics of a work zone ITS application can be categorized as follows:MobilitySafetyTraveler informationSystem performance
• #12 Although mobility is one of the key benefits of using smart work zones, it is often the mostdifficult benefit to quantify. The primary metrics used to evaluate work zone ITS deploymentsin t4rms of how well they improve mobility include:Rate of diversion (traffic volumes on mainline and alternate routes)DelaySpeedsWork zone throughputTravel timeReduced demandUser surveysIncidents within the work zone and at the approachesMaximum queue lengthsExtensive coverage of detector and surveillance equipment to collect data is not always availablein a work zone. Before and after studies can be used to determine the affects if the system isdeployed some time after the work activity has already commenced. Many agencies use thechange in traffic volumes on alternate routes as a proxy to measure how effective work zoneATIS is in changing driver behavior. It appears that the most widely used method of measuringthe effectiveness of work zones equipped with ITS in improving mobility is through driversurveys.
• #13 Deploying agencies are sometimes reluctant to quantify specific crash reduction goals in workzones, and the data is not always available in a comprehensive and timely enough manner foranalysis. It is also often difficult to determine whether or not a particular crash was caused bythe work zone, or if the contributing factors would have led to the crash without it. The obviousdifficulty of quantifying how many crashes were avoided is evident. The metrics which can beused to evaluate safety include:Number of crashesCrash rateCrash severityCitationsReduction in observed aggressive maneuvers and forced mergesMany agencies have begun using the reduction of aggressive behavior as a safety metric. Thiscan be a rather subjective measure, but can be estimated by simulation modeling, or quantifiedby personal observation or review of recorded video data from before and after deployment ofthe system.
• #14 The effectiveness of information dissemination from a smart work zone is an important measure and one that correlates closely with the degree of customer satisfaction achieved from the system. How many drivers are getting the information, how useful it is to them, and how much impact their use of the information has on the safety and mobility of the work zone can often be measured by customer surveys. Survey questions can be asked of motorists on-site at locations near the work zone, such as nearby rest areas or truck stops, by telephone, mail or e-mail. Surveys can be targeted at specific groups, such as private citizens or commercial vehicleoperators. Useful information can also be gathered from observation, and from law enforcement, contractor, and construction management interviews.Example questions, such as the following from the I-30 Little Rock to Benton Construction Zone Survey, can be used to assess the effectiveness of information dissemination:17 Have you ever read the electronic message signs?Rate your level of agreement/disagreement with the following statements about the electronicmessage signs:  The messages are EASY to understand. The messages are ACCURATE. The messages are DETAILED enough to help me make decisions about my route The signs are located in the right places to help me make decisions about my route. Because of the info on the signs, I am better prepared to react to slow or stopped traffic. I feel safer traveling through this construction zone because of the information on the signs. Just having the information makes me feel less bothered by the delays in the constructionzone.Have you ever tuned into the highway advisory radio? The radio broadcast quality is too poor to hear properly. The messages are USEFUL. The messages are ACCURATE. The messages are updated frequently enough. The messages are DETAILED enough to help me make decisions about my route.Visits to project websites can be counted to track the number of unique visitors, the number ofreturn visitors, the types of information they are accessing, and the days and times they areusing the website. An on-line survey can also be included on the project website. Thesemethods can all be used to determine what information is deemed the most useful by the public.
• #15 System performance is a measure of how well the system operates during its deployment. If thesystem is not working properly, its effectiveness in improving safety and mobility through thework zone is compromised. Ease of installation and maintenance, and the lack of unplannedoutages can be measure by:Error logsMissing dataDown timeProductivityWorkers’ exposure to hazardsConstruction efficiencyUser perspectives on system performance, functionality, and benefits to motorists.
• #16 Sample report data: This table lists speed data in the southbound direction at data collector #9 just south of Hwy 463 on I55. A report was ran Monday morning from 6am to 8am