Institute for Transportation

About the research

Back-of-queue crashes are a significant safety hazard in highway work zones—especially those with intermittent congestion. A number of intelligent transportation systems (ITS) have been developed to provide queue warning, but historically the cost and complexity of these systems have limited their use.

The objective of this project was to design a low-cost queue warning system (QWS) to reduce costs, simplify deployment, and test in the field. The developed low-cost QWS could allow back-of-queue warning signs to be installed wherever queuing is anticipated (even for short-term projects). Modular design of the low-cost QWS will allow the system to be extended as far upstream as necessary to provide ample driver notification in high-, medium-, and low-demand situations.

The sign support system for a low-cost QWS went through several iterations of design in order to find a design that has been crash tested and approved to the Manual for Assessing Safety Hardware (MASH) standards. The final design of the sign support system is based on a non-proprietary support system crash tested by the Texas A&M Transportation Institute. The proposed sign support design for the low-cost QWS has not been able to be field tested for several reasons. The most notable reason is highway agencies are strongly encouraged for safety and liability reasons to only use hardware systems that have successfully completed crash-testing protocols in accordance to the safety standards in the MASH. To date, only a select few sign support systems have been crash tested to MASH criteria, and none with the type of low-cost QWS hardware required for this prototype.

The second reason was the inability to find field test sites on conventional two-lane highways with 55 mph speed limits and the requirement that the equipment be located outside of a clear zone or shielded by protective barriers. Expressway and freeway facilities can’t be used for testing for this design because the Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD) requires larger size signs and font letter sizes for the message required on these types of facilities. Therefore, before field testing can be undertaken on highways open to traffic, an investment in funding for crash testing is strongly recommended.

About the research

The objective of this research project was to design, develop, and deploy the Smart Work Zone Activity app (SWiZAPP), which is a cross-platform mobile application for collecting, reporting, and posting accurate, real-time, work-zone activity information and status. The app is enabled with functionalities for managing an unlimited number of construction work zones due to its scalable, cloud-based design architecture. It supports work-zone geolocation and mapping via on-board GPS sensors and Google Maps, respectively. Users of the app can post live activities from construction sites by taking snapshots and uploading images, utilizing buttons within the app’s interface to indicate traffic conditions and lane activities, or text messaging via the app. SWiZAPP also enables its users to view both real-time and historical activities of all work zones in the SWZDI states.

This document includes a user manual, as an appendix, to access and use SWiZAPP for work-zone activity monitoring. The user-friendly interface includes standard work-zone procedures and is suitable for use by both department of transportation (DOT) staff and contractors.

The benefits from the successful deployment of SWiZAPP include more accurate and timely work-zone information for work-zone management, traveler information, inspections, contract monitoring, safety analysis, and project coordination.

About the research

Each year, billions of dollars are spent by public agencies, utilities, and private developers for projects that affect pedestrian safety and mobility during construction. A systematic literature review was conducted to identify previous research related to work zone pedestrian safety and mobility deficiencies and potential solutions. Studies published between 2004 and mid-2021 (17½ years) were eligible for inclusion. Only nine studies meeting the inclusion criteria were found. One study summarized research conducted prior to 2006, five discussed physical design and traffic management for temporary pedestrian facilities, and three discussed electronic mobility aids for visually impaired pedestrians. None of the identified studies provided quantitative evaluations of the effectiveness of proposed design solutions. The qualitative findings described in the studies are often subjective, and the study designs have significant risk of bias.

A supplemental literature review compared the work zone design guidance issued by state departments of transportation (DOTs). The guidelines ranged widely in scope and specificity. The most detailed guidance tended to be issued by more urbanized states and was mainly derived from a temporary pedestrian access handbook prepared by the Minnesota DOT around 2011.

Several research needs related to pedestrian safety and mobility in work zones were identified. For example, there is currently virtually no information on positive or negative effects of relaxing design standards when a pedestrian facility will be used for only a short duration. In addition, current design guidance for temporary facilities is not tied to objective criteria such as pedestrian traffic volume, motor vehicle traffic volume, traffic speeds, facility type, or work duration.

A Pedestrian Test Track is proposed as a potential method for gathering information about user acceptance of proposed design solutions.

About the research

Engineering practitioners must balance safety and mobility when evaluating different construction phasing alternatives for highway work zones. There is a need for practitioner guidance and practical tools to assess work zone safety impacts as such resources are currently lacking. The objective of the study was to extend a structured safety assessment tool that was previously developed for freeways, expressways, and rural two-lane highways to include other facilities such as arterials, signalized intersections, unsignalized intersections, multi-lane highways, and ramps. Using Missouri data, this study introduces five new crash prediction models for work zones on urban multi-lane highways, arterials, ramps, signalized intersections, and unsignalized intersections. All the work zone models in this report are proposed for the first time. These work zone models are implemented in a user-friendly spreadsheet tool that automatically selects the appropriate model based on user input. The tool predicts crashes by severity, and computes the crash costs for each construction phasing alternative.

About the research

This project validated the Highway Capacity Manual (HCM) work zone capacity methodology for urban and rural freeways and provides recommendations for a more accurate estimation of work zone capacity. This study collected data from 16 work zone sites across Iowa in 2018 and 2019. The free flow speeds (FFSs), capacities, and queue discharge rates (QDRs) at these work zones were calculated using the HCM method and compared to field measurements.

For the work zones considered in this study, the key findings are as follows:

• FFSs estimated using the HCM method had a greater variance than the field-measured values. Under free flowing conditions, Iowans generally drove around the work zone speed limits, while the HCM method predicted a wide range of FFSs.
• The field-measured prebreakdown capacities and QDRs were significantly lower than the values computed using the HCM method, indicating that traffic breakdown could happen at a much lower flow level than the capacity predicted by the HCM method.
• With complex work zone configurations, such as narrow lanes, lane shifts, and crossovers, the observed FFS and prebreakdown capacity were significantly lower than typical work zone configurations.

About the research

Travel time reliability studies have garnered interest in recent years with researchers and practitioners recognizing reliability as a trait of significant importance to commuters. Presence of work zones can significantly impact the capacity and speeds at the location and consequently impact travel time reliability. This study built a framework for studying impacts of work zone on travel time reliability. The framework covers aspects of work zone selection, evaluation of work zones, derivation of travel time distributions for each work zone, and developing a predictive model for work zone impact on travel time reliability. Work zone and travel time data were collected from 19 freeway and highway work zones across the state of Wisconsin. Supporting hourly traffic counts were collected for the work zones where available. Average travel time trends through a day, travel time distribution, and reliability metrics were studied at each candidate location individually to observe the impacts of the work zone. Reliability measures from across all work zones were combined to study discernible relationships between the change in reliability measures caused due to the work zone and a variety of work zone properties, and predictive regression models were developed to estimate work zone impact on reliability. Due to limitations in the quality and quantity of data available, the regression modeling yielded moderate goodness of fits. A larger dataset and/or availability of detailed work zone information might result in better travel time reliability models. The report presents limitations and findings from the study and informs on quality of data that needs to be collected for future studies on work zone travel time reliability.

About the research

Roadway lanes are often repositioned to accommodate highway work operations, resulting in a need to alter pavement markings. Even the most effective methods for removing old pavement markings sometimes leave “ghost” markings at the old lane line locations. The ghosts can be quite conspicuous under certain lighting conditions and viewing angles. To address this issue, some international jurisdictions use a special marking color (orange or yellow) to increase the salience of temporary lane lines; this practice appears to have originated in Germany in the 1980s and is now routine in several European countries and the Canadian province of Ontario. Special-color markings have also been used experimentally in Australia, New Zealand, and Quebec. In some jurisdictions the special-color markings override existing markings (such that the old markings are left in place), while other jurisdictions use special-color temporary marking but also attempt to remove old lane lines. The Wisconsin Department of Transportation (WisDOT) experimented with orange work zone marking on a high-volume long-term freeway-to-freeway interchange reconstruction project in Milwaukee; surveys indicate good driver acceptance, but the complex traffic flow characteristics and frequent configuration changes at the site make it difficult to separate the effects of the orange markings from other aspects of the work zone management strategy. To assess the driver behavior aspects of orange markings in a simpler environment, a matched-pair study was conducted on two bridge re-decking projects on I-94 near Oconomowoc, Wisconsin. Evaluation of vehicle positioning and speed data indicated very similar driver behavior with the two colors. Driver surveys and interviews with project field engineers indicated a preference for the orange marking when lateral lane shifts are required. Perhaps the most pragmatic approach is to reserve orange as an emphasis color for specific work zone locations that require difficult driving maneuvers.

About the research

The Highway Safety Manual (HSM) is the compilation of national safety research that provides quantitative methods for analyzing highway safety. The HSM presents crash modification functions related to freeway work zone characteristics such as work zone duration and length. These crash modification functions were based on freeway work zones with high traffic volumes in California.
When the HSM-referenced model was calibrated for Missouri, the value was 3.78, which is not ideal since it is significantly larger than 1. Therefore, new models were developed in this study using Missouri data to capture geographical, driver behavior, and other factors in the Midwest. Also, new models for expressway and rural two-lane work zones that barely were studied in the literature were developed.

A large sample of 20,837 freeway, 8,993 expressway, and 64,476 rural two-lane work zones in Missouri was analyzed to derive 15 work zone crash prediction models. The most appropriate samples of 1,546 freeway, 1,189 expressway, and 6,095 rural two-lane work zones longer than 0.1 mile and with a duration of greater than 10 days were used to make eight, four, and three models, respectively.

A challenging question for practitioners is always how to use crash prediction models to make the best estimation of work zone crash count. To solve this problem, a user-friendly software tool was developed in a spreadsheet format to predict work zone crashes based on work zone characteristics. This software selects the best model, estimates the work zone crashes by severity, and converts them to monetary values using standard crash estimates.

This study also included a survey of departments of transportation (DOTs), Federal Highway Administration (FHWA) representatives, and contractors to assess the current state of the practice regarding work zone safety. The survey results indicate that many agencies look at work zone safety informally using engineering judgment. Respondents indicated that they would like a tool that could help them to balance work zone safety across projects by looking at crashes and user costs.

About the research

Several work-zone traffic control devices have not yet been evaluated to the American Association of State Highway and Transportation Officials’ (AASHTO’s) Manual for Assessing Safety Hardware, Second Edition (MASH 2016) safety performance criteria. Devices commonly used by Smart Work Zone Deployment Initiative state sponsors were summarized. A non-proprietary Type III barricade was selected for testing, as no non-proprietary barricades had been evaluated to MASH 2016. The Type III barricade had 8-ft (2.4-m) long plastic barricade panels, a 30-in. x 48-in. (762-mm x 1,219-mm) aluminum sign attached to the top two plastic barricade panels. The 2-in. (51-mm) square legs and 1¾-in. (44-mm) square uprights were 14-gauge perforated square steel tube. The barricade also had two warning lights attached at the top of each upright. The Type III barricade was tested to MASH 2016 test designation no. 3-71 with a 2,426-lb (1,100-kg) small car. One barricade was impacted at a speed of 64.7 mph (104.1 km/h) and at an impact angle of 90 degrees, and the other barricade was impacted at a speed of 61.2 mph (98.5 km/h) and an impact angle of 0 degrees. Both tests successfully met all evaluation criteria in MASH 2016 for test designation no. 3-71.

About the research

The main objective of this synthesis was to identify and summarize how agencies collect, analyze, and report different work-zone traffic-performance measures, which include exposure, mobility, and safety measures. The researchers also examined communicating performance to the public. This toolbox provides knowledge to help state departments of transportation (DOTs), as well as counties and cities, to better address reporting of work-zone performance.