CHAPTER 2

Use Cases

The project team identified seven major work zone technology use cases that could encompass the currently available work zone technologies:

• Traveler information systems (speed and travel time),
• Queue warning systems,
• Work zone intrusion alert systems,
• Work zone presence systems,
• Speed harmonization systems,
• Speed compliance systems, and
• Dynamic merge assistance systems.

This chapter briefly describes each of these use cases and the level of maturity of SWZ technologies in each. The goal of this effort was to develop guidance on emerging technologies that are not already mature. The maturity of an SWZ technology was defined as its readiness for scaled-up deployment The FHWA Technology Readiness Level approach was used to develop this guidance (Towery et al. 2017), and SWZ technologies were rated on a four-point scale ranging from 0 to 3 (0 = experimental concept, 1 = basic research and controlled laboratory testing, 2 = pilot tests in the field, and 3 = commercial availability).

SWZ technologies in each of the use cases are further categorized by type as data generation or data dissemination. Data generation refers to SWZ technologies that are used to collect and generate data about work zones, such as traffic speed, volume, and other relevant data points. These data are typically collected by sensors, cameras, or other types of monitoring equipment and are used to inform decisions about work zone operations and safety. Data dissemination refers to SWZ technologies that are used to communicate work zone information to drivers and other road users. This information may include real-time traffic updates, detour information, and other relevant information to help drivers navigate through work zones safely and efficiently. This information can be disseminated through a variety of channels, including variable message signs, mobile applications, CAV, and other digital platforms.

Traveler Information Systems

Traveler information systems provide data to drivers on the travel conditions in a work zone in real time. Data can be generated by probe data and infrastructure-based sensors. Data for these systems can be disseminated via a 511 system or other state traveler information systems, dynamic messaging signs (DMSs), smartphone applications, emails, text messages, or CAV in-vehicle messaging. Traveler information systems are often deployed with other systems such as queue warning systems and systems that monitor and communicate information on work

Table 1. Technology applicability summary: Traveler information systems.

zone conditions. Traveler information systems can be deployed on all roads. Table 1 summarizes technologies used for traveler information systems rated by maturity.

Queue Warning Systems

Queue warning systems inform drivers of the presence of congested traffic downstream on the basis of real-time traffic conditions. Data on traffic conditions such as the formation of queues, length of queue, and the speed of traffic at the approach to a work zone can be provided by point detectors (most commonly side-fire radar), crowdsourced private-sector probe data, and CAV data. Queue warning systems are often deployed on high-speed roadways such as Interstates and expressways, as conflicts between high-speed approaching traffic and the end of a queue are a significant safety concern.

Because the resulting data about traffic queues may be disseminated in a variety of ways, defining a standard path has been challenging. Drivers might be alerted to conditions locally by static signs with warning lights or DMSs, or through in-vehicle messaging if CAV radio transmission is available. If the queue warning system is equipped to transmit data to a cloud service, data could be made available to smartphone applications or CAV traveler information systems. At this time, the current Work Zone Data Exchange (WZDx) Version 4.1 standard does not directly support the management of traffic queue system information. There are data objects that address a generic traffic sensor, but the standard lacks specifics on queue metrics and message presentation information that may be derived from queue warning systems. However, there is the potential to add this information to the WZDx in the future.

Depending on the system configuration deployed, queue warnings could be provided as a stand-alone system or as part of a larger traveler information system that would better support dissemination including fleet vehicles. Table 2 summarizes how possible technologies used for queue warning detection and information dissemination are rated by maturity.

Table 2. Technology applicability summary: Queue warning systems.

^a 0 = system is still in research and development or no data were available.

Work Zone Intrusion Alert Systems

Intrusion alarms or alerts allow workers and motorists to be notified of a dangerous threat through audible or haptic notifications. For some devices, sensors placed on the perimeter of a work zone algorithmically determine whether a vehicle approaching a work zone is traveling at a speed that puts workers at risk if it cannot or does not slow in time. Commercially available work zone intrusion alert systems (WZIASs) have been evaluated and have been found to have mixed results. In general, there are two types of WZIAS, each defined by its method of detecting intrusions. One type can provide advance notifications to workers by predicting an intrusion before it occurs. The second type provides alerts to workers after a vehicle enters the work zone’s perimeter. The technologies can be broken down further by the type of technology they employ for detection. Kinematic systems utilize sensors and other monitoring equipment to detect the movement and speed of vehicles entering the work zone. Pneumatic systems use sensors placed on the pavement that are activated when a vehicle passes over them. When a vehicle passes over the sensor, it triggers a signal that activates a warning device. Beyond the method of detection lies the method of notification. There are multiple notification mechanisms for how workers are alerted to intrusion threats, including, but not limited to, flashing lights, audible alarms, radio notifications, and personally worn device alerts. Alert mechanisms are not mutually exclusive either, as human factors requirements often recommend a redundant mechanism or alert method. Most of these technologies also have both a data generation component and a data dissemination component because they can detect as well as alert the users. As noted in the current study, and as was stated by Nnaji et al. (2020) in their systematic review of work zone safety technologies, studies on cost-effectiveness are lacking. Such information requires a DOT to make an investment in a technology as an intervention and provide before and after data. For WZIAS, it may be too soon to expect cost-effective insights. Furthermore, deployment of these technologies may also be limited by concerns regarding feasibility of use in a mobile work zone (Boodlal et al. 2020). Table 3 summarizes technologies used for WZIAS by the type of activation and rates their maturity across all taxonomy categories.

Work Zone Presence Systems

Work zone presence systems detect and disseminate information about the presence and configuration of a work zone to drivers. Most of these systems are capable of data generation as well as data dissemination and could be deployed on all roadway types. Table 4 summarizes technologies used for systems that detect work zone presence rated by maturity.

Table 3. Technology applicability summary: WZIAS.

Table 4. Technology applicability summary: Work zone presence systems.

Speed Harmonization Systems

Work zone speed harmonization systems, including variable speed limit (VSL) systems, broadly attempt to (1) provide guidance on appropriate safe speeds on the basis of current conditions and (2) encourage more uniform speed selection, thereby improving flow and safety. To achieve these goals, recommended speeds are usually set dynamically on the basis of current work zone and congestion conditions. Most current field deployments of work zone VSLs and speed harmonization systems have relied on a series of point detectors to collect data used to define recommended speeds. CAV-based speed harmonization has been examined on a more limited basis through simulation efforts and limited field tests. Most field-deployed systems provide information on recommended speeds through dynamic speed limit signs placed at fixed locations and on supplemental websites, but emerging CAV approaches provide in-vehicle guidance and control. The current state of the practice is to deploy speed harmonization systems on specific projects where operational or safety issues are expected. These systems have been deployed and evaluated on freeways; no arterial applications were identified. Table 5 summarizes how the maturity of possible technologies used to generate speed harmonization information and for information dissemination is rated across all taxonomy categories.

Speed Compliance Systems

Speed compliance systems monitor vehicle speed by using radar to track vehicles passing at a given location within a work zone. These systems can be deployed for both advisory and regulatory purposes. In the case of the advisory system, a variable message sign or speed feedback

Table 5. Technology applicability summary: Speed harmonization systems.

^a 0 = system is still in research and development or no data were available.

Table 6. Technology applicability summary: Speed compliance systems.

^a 0 = system is still in research and development or no data were available.

trailer provides a digital readout of approaching vehicle speeds that is updated as each vehicle passes. Most advisory message signs also flash when the speed exceeds the speed limit threshold or may switch to a “slow down” message, depending on the product brand. When deployed for regulatory purposes, the system utilizes photo enforcement technology to read the license plate and transmit violation information to a back office administrative system that will issue a citation to the owner of the violating vehicle. Regulatory speed compliance systems are most effective when signage is deployed upstream of the system location, indicating that photo enforcement is in effect within the work zone. The use of photo enforcement speed compliance systems is not legal in every jurisdiction, so there may be limitations on the application of this technique. Table 6 summarizes technologies used for systems that detect work zone conditions and rates their maturity.

Dynamic Merge Assistance Systems

Dynamic merge assistance systems attempt to (1) provide guidance on lane usage on the basis of real-time work zone and traffic conditions or (2) encourage smoother merging by creating appropriate gaps, thereby improving work zone throughput, reducing traffic congestion, and mitigating safety concerns. To achieve these goals, recommended merge strategies (e.g., early or late merges) are usually activated dynamically on the basis of real-time work zone and traffic conditions. Current field deployments of dynamic merge assistance systems for work zones usually rely on a series of traffic sensors to collect data used to determine corresponding merge strategies. CAV-based dynamic merge assistance has been evaluated on a more limited basis, mostly through simulation efforts and limited field tests. Most field deployments disseminate merge strategy information by using both static signs with dynamic flashers and DMSs placed at strategic locations. Emerging CAV-based approaches, on the other hand, provide either in-vehicle guidance (for human-operated vehicles) or governance over the cooperative merging process (for autonomous vehicles). The current state of the practice is to deploy DMSs with supplemental static signs (equipped with dynamic flashers) at work zones expected to have operational issues. These systems have been deployed and evaluated on both freeways and arterials. Table 7 summarizes how possible technologies used for collecting dynamic merge assistance information and for information dissemination are rated by maturity.

Table 7. Technology applicability summary: Dynamic merge assistance.

^a 0 = system is still in research and development or no data were available.