Researchers
John Shaw
About the research
Rear-end collisions in work zones, induced primarily by speeding and tailgating, are a predominant concern for roadway safety. Although considerable research has shed light on the dangers and implications of speeding within these zones, there exists a conspicuous research gap on tailgating behaviors.
To address this gap, the present project was conducted in two main phases. In the first phase, a message design and comprehension test involved the development of graphics and messages tailored for both fixed signs and dynamic message signs (DMS). These messages were constructed to ensure not only that drivers understood them with ease but also that the messages emotionally resonated with drivers and conveyed positive sentiments. In the subsequent field test phase, the designed signs were installed in work zones to evaluate their effectiveness in real-world settings. Two key performance metrics, namely, the average vehicle headway and the probability of tailgating occurrences, were used for this evaluation.
Preliminary surveys among potential users indicated a strong inclination towards messages with a positive tone and without numerical specifics, underscoring the importance of the messages’ lucidity and favorable reception. Field evaluations carried out at single-lane closure and shoulder closure construction sites demonstrated the efficacy of the signs evaluated in the surveys. There was an increase in average vehicle headway and a reduction in the probability of tailgating occurrences at both sites. Collectively, this research provides meaningful insights into tailgating behaviors in work zones, bridging the knowledge gap and laying a foundation for work zone safety strategies.
Researchers
John Shaw
About the research
Highway work zones often have major safety and mobility impacts, which are made worse when travelers are unaware that they are approaching a work zone. To monitor and mitigate the mobility and safety impacts of road construction, transportation agencies, first responders, and the public require accurate information about the location, extent, and timing of construction-related closures.
This project reviewed various stakeholders’ current needs for pre-construction, real-time, and post-construction work zone information and compared these needs to the available work zone data sources and standards. The analysis identified a substantial mismatch between the roadway and lane closure data currently available and the data required to manage work zone traffic impacts effectively. To address this gap, the project developed a conceptual prototype for a tool that would facilitate self-reporting of closure details by contractors and maintenance crews.
Researchers
About the research
Rear-end crashes are one of the primary crash types in work zones and frequently occur at the back-of-queue (BOQ). Some agencies have utilized back-of-queue warning systems (QWSs), where real-time sensors are located upstream of stopped or slowed traffic, either to actually detect BOQs or monitor conditions to predict BOQ locations. QWSs then provide notifications of traffic conditions to drivers, which ideally lead to lower speeds and drivers being prepared to react to the BOQ, resulting in fewer crashes and conflicts. However, a driver needs to be properly monitoring the roadway environment to receive the warning and, then, needs to be prepared to take the appropriate actions when necessary. In many cases, drivers are distracted and fail to recognize warnings, or they receive the warning but fail to comply with appropriate speeds. As a result, one of the main needs to address BOQ situations is to understand what drivers are doing so that a QWS can get a driver’s attention. Additionally, driver behavior may indicate that other countermeasures, such as speed management, may be as effective as formal QWSs. The research described in this report aims to address this knowledge gap through the following objectives:
- Identify common types of QWSs
- Summarize QWSs used in Smart Work Zone Deployment Initiative (SWZDI) states
- Identify driver behaviors in BOQ scenarios
- Make recommendations
- Summarize needs for connected vehicle applications
Safety critical events (SCEs) were evaluated for back-of-queue situations using two different datasets. The first was a set of BOQ SCEs that were reduced from camera image captures at BOQ locations in work zones in Iowa during the 2019 construction season. Analysis of these data indicated speeding, following too closely, and forced merges were the primary characteristics associated with BOQ. The second dataset was an analysis of BOQ events in the second Strategic Highway Research Program (SHRP2) Naturalistic Driving Study (NDS). Analysis of these data indicated that following too closely and glances away from the roadway task of 1 or more seconds were statistically significant.
Researchers
John Shaw
About the research
In the Work Zone Activity Data Logging Phase I project, state transportation agencies in the SWZDI states and beyond expressed a strong need for better information about the location, extent, and timing of lane closures. More than a dozen use cases for detailed lane closure data were identified and prioritized, such as helping first-responders avoid closures, providing more accurate public information about closure locations and timing, and more efficiently conducing post-construction work zone traffic management effectiveness reviews. Phase I affirmed that the vast majority of state DOTs currently lack the ability to track lane closures at the level of temporal and spatial detail required for these uses. Among the very few agencies that have the technical ability to record this information, the data lacks reliability. Closures on county and municipal routes were seldom, if ever, tracked.
Phase I showed that existing data sources are not sufficient to support the high-priority use cases. For example, although underperforming work zones sometimes show up in traffic management center (TMC) delay data, it is difficult to distinguish work zone delays from delays caused by traffic crashes. Since the exact closure location, timing, and extent are seldom recorded, even agencies with lane closure permitting systems are experiencing great difficulty relating work zone performance to closure characteristics. Moreover, TMC databases provide almost no information about well-performing work zones, making it extraordinarily difficult to pinpoint factors of success.
To address these needs, the Phase I project gathered information about existing work zone data sources, identified relevant standards, and developed a series of sketches that lay out a vision for an easy-to-use lane closure data collection application or website. The goal of this project is to transform these conceptual sketches into a working prototype that generates data in a format that could eventually be integrated with TMC data and other existing data sources to provide a more complete picture of work zone performance.
Researchers
Madhav Chitturi
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.
Researchers
Yaw Adu-Gyamfi
Carlos Sun
Praveen Edara
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.
Researchers
John Shaw
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.
Project Details
12/01/16
08/31/18
Smart Work Zone Deployment Initiative
Researchers
Henry Brown
Carlos Sun
Praveen Edara
Roozbeh Rahmani
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.
Researchers
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.
Project Details
01/01/17
06/01/18
Smart Work Zone Deployment Initiative
Researchers
Soyoung Ahn
Madhav Chitturi
Anupam Srivastava
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.