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Public Roads - Spring 2021

Spring 2021
Issue No:
Vol. 85 No. 1
Publication Number:
Table of Contents

CarmaSM: Improving Traffic Flows and Safety at Active Work Zones

by Pavle Bujanović, Todd Peterson, and Denise Bakar

FHWA's CARMASM Program is testing how cooperative driving automation can manage work zone congestion and enhance safety.

Developed by the Federal Highway Administration, the CARMASM Program is leading research on the information exchanges and cooperative maneuvers that constitute cooperative driving automation (CDA). Defined by the Society of Automotive Engineers J3216 Standard, CDA aims to improve the safety, flow, and efficiency of roadway infrastructure by supporting the cooperative movement of automated vehicles through the use of wireless mobility applications. Through software development activities, the program is building numerous CDA features (or applications) that will be tested in a set of research tracks focused on transportation systems management and operations. The research tracks aim to demonstrate the potential of CDA to facilitate system efficiency and safety improvements in various areas of the transportation ecosystem.

The work zone management (WZM) use case is part of the CARMA Reliability research track. This research track examines solutions to nonrecurring congestion on freeways and arterials, such as traffic incidents and inclement weather, in addition to work zone activity. The WZM use case will demonstrate the role of CDA in improving safety and alleviating work zone-related congestion. The program is addressing multiple WZM scenarios, with each scenario demonstrating improved network performance through the application of a specific CDA feature.

"The application of CDA to work zone management has been among the most challenging cases for automated vehicle operations. The CARMA WZM use case lays a foundation for addressing this challenge, which is critical to expanding the applicability of CDA to other environments," says Dr. Xiaopeng Li, an associate professor at the University of South Florida and director of the National Institute for Congestion Reduction, whose team is developing CDA algorithms that will be tested in the CARMA ecosystem.

FHWA's fleet of CARMA vehicles includes a freight truck and four passenger vehicles. Source: FHWA.
FHWA's fleet of vehicles equipped with the CARMA Platform are helping researchers test how cooperative driving automation can relieve work zone congestion and improve safety.

The Work Zone Scenario

The first scenario developed under the WZM use case involves a one-lane, two-way traffic taper resulting from an active work zone on a two-lane arterial street. This scenario calls for an active work zone to occupy a segment of one lane, requiring vehicles equipped with a cooperative automated driving system (C-ADS) to temporarily merge into the lane traveling in the opposite direction to pass the work zone lane closure. To accomplish this, the vehicles must communicate with CARMA CloudSM and CARMA Streets to ensure that it is safe for them to enter the work zone. Vehicles are equipped with C-ADS technology through the installation of CARMA PlatformSM, which bestows the Society of Automotive Engineers ADS Level 3+ functionality.

The work zone scenario proceeds as follows: The vehicles equipped with C-ADS are traveling on a two-lane arterial that contains a work zone. At one section in the arterial, one of the lanes is closed. Stationed at either end of the work zone are two temporary traffic signals; the traffic signals are synchronized and have fixed timing to allow only one direction of traffic to proceed through the work zone at a time. A future application will explore use of adaptive traffic signal timing based on the presence of vehicles in each direction.

Cars pass through a simulation of a work zone during CARMA testing. Source: FHWA.
Researchers tested CARMA Platform-equipped vehicles in a simulated work zone.

The vehicles regularly transmit location information, via their onboard units, to CARMA Cloud through V2X [vehicle-to-everything] Hub. V2X Hub is a separate, multimodal open-source software system, stored in roadside infrastructure such as traffic cabinets, which enables networked, wireless communications between participating entities. As the vehicles approach the traffic signals near the work zone, CARMA Cloud prepares a message containing information about the work zone lane closure in the intended direction of the vehicles. The message identifies the virtual perimeter (geofence) for the work zone and contains recommended movement information for vehicles traveling through the geofence—this includes a low speed advisory and alternative lane geometry. CARMA Cloud transmits the message to V2X Hub for broadcast to the approaching vehicles. The vehicles receive the message via their individual onboard units.

Traffic signals deployed on either end of the work zone control traffic movement in the work zone. For example, the vehicles in the lane with the closure receive the traffic green light to proceed, while the vehicles in the opposite lane remain stopped at a red light. The moving vehicles use the recommended movement information from CARMA Cloud to cross the yellow line separating the travel lanes, merge to the opposite lane, travel at the advised speed through the work zone, and merge back into their original lane after clearing the geofenced area.

A diagram indicating how traffic flows in alternating directions around a work zone that blocks a lane on an arterial roadway. Source: FHWA.
The first work zone management use case involves a one-lane, two-way traffic taper. Vehicles traveling on the side of the road blocked by the work zone must merge into the lane traveling in the opposite direction.
*SPAT is defined as Signal Phase and Timing.

Once the traffic signal in the closed lane changes to red, there will be a brief "all red" period during which both directions face a red signal. This ensures that there are no vehicles still passing through the work zone when the opposite direction receives a green signal. After this brief period, the vehicles in the open lane receive a green signal to proceed through the work zone. The moving vehicles reduce their speed to meet the low speed advisory and drive through the work zone area. After passing through the work zone and exiting the geofenced area, vehicles in both directions continue to travel in their respective lanes at the posted speed limit.

A diagram indicating how traffic flows in alternating directions around a work zone that blocks a lane on an arterial roadway. Source: FHWA.
The first work zone management use case involves a one-lane, two-way traffic taper. Vehicles traveling on the side of the road blocked by the work zone must merge into the lane traveling in the opposite direction.
*SPAT is defined as Signal Phase and Timing.

This traffic control pattern continues for the duration of the lane closure due to the active work zone.

To direct the safe passage of vehicles through active work zones, the scenario employs the Work Zone Data Exchange message specification, which leverages cloud services to facilitate information exchanges between vehicles, infrastructure, and road users. To ensure that the features operate safely and in the way they were designed for this specific operational design domain, the CARMA team conducted functional tests prior to validation testing of the CDA features required for the scenario.


The CARMA Program leverages collaboration with stakeholders in government, academia, consulting, and the technical industry to accelerate advancements in CDA research, development, and testing. The program's CARMA Collaborative effort teamwork through multiple touchpoints, from webinars and group meetings to conferences and panels. CARMA products, which are open for collaboration on the GitHub development platform (, are included in the Open Source Software Suite for Intelligent Transportation Systems (OSS4ITS), available at Deployers can use, reuse, and augment the tools to help accelerate their programs.

Looking Ahead

The introduction of CDA is expected to produce numerous positive impacts to the movement of people and goods on the Nation's roads. The WZM use case establishes the framework of using CDA features in active work zone areas to ease congestion and enhance traveler and worker safety.

"Better communication between vehicles and work zone safety devices through CARMA will improve safety and vehicle performance though roadway work zone installations, making it safer for workers as well as motorists," says David Rush, manager of the Work Zone Safety Program at the Virginia Department of Transportation.

The WZM use case highlights the enhanced response actions—made possible through CDA—to traffic disruptions caused by work zones. These enhanced response actions, which include improved awareness and coordinated movements of vehicles in a work zone, will ultimately lead to improvements in traffic performance by reducing congestion and incident occurrence in work zones.

"Ultimately, the success of testing will bring the Nation one step closer to deploying CDA-based transportation systems management and operations strategies for managing work zone traffic," says Barb Wendling, chair of the newly formed Society of Automotive Engineers Cooperative Driving Automation System Committee.

A man stands at a work station beside one of FHWA's fleet of CARMA vehicles. Source: FHWA.
An engineer performs CDA research using a CARMA Platform-equipped vehicle at the FHWA Saxton Transportation Operations Laboratory.

Pavle Bujanović is a CARMA technical manager in FHWA's Office of Operations Research and Development, managing various CDA research projects and leading the new CARMA Reliability research track that includes work zones. He earned a B.S. in civil engineering from Syracuse University, an M.S. in sustainable design and construction from Stanford University, and a Ph.D. in transportation engineering from the University of Texas at Austin.

Todd Peterson is a transportation specialist for the Office of Operations' Work Zone Management Program. Todd leads FHWA's Work Zone Data Initiative, which has produced a data specification and national deployment framework for real-time information pertaining to work zone activity, and is currently leading a project to expand that effort to other nonrecurring events. He earned a B.S. and an M.S. in civil engineering from Virginia Tech.

Denise Bakar is a contracted communications specialist in FHWA's Saxton Transportation Operations Laboratory, leading content strategy and outreach activities. She earned an M.A. in strategic communications from American University and a B.A. from the University of Virginia.

For more background on CARMA, see "CARMASM: Driving Innovation" in the Winter 2020 issue of Public Roads.