CHAPTER 6

Automated Work Zone Crash Attenuation

6.1 Description of Automated Work Zone Crash Attenuation

Trucks equipped with truck-mounted attenuators (TMAs) are driven by human drivers who follow behind highway maintenance vehicles. Typically, TMA-equipped vehicles are used to shadow a work zone, with the crash attenuator mounted to the rear of the vehicle to absorb the impact of a rear-end collision. TMAs thus shield workers and equipment from vehicles crashing into the back of maintenance vehicles or into the work zone. However, while TMAs can reduce crashes and save lives, they still pose a risk for drivers of TMA-equipped vehicles. To reduce the impact on drivers, automated truck-mounted attenuators (ATMAs) are being tested by different organizations to enhance the overall safety in work zones (Figure 6-1).

At least one vendor has developed an ATMA. The system includes a vehicle control module; actuators to control steering, braking, and acceleration; a transmission controller; a radio transceiver; and a navigation module. The system is operated by a lead vehicle that maneuvers the ATMA into position. The ATMA initially has to be driven into place by a human driver, and then the automation system is turned on and the ATMA is connected to the lead vehicle (Kenter 2017).

6.2 Examples of Automated Work Zone Crash Attenuation

Information about how agencies have evaluated the use of automated work zone crash attenuation was gathered from three sources: (1) a review of the literature, (2) a survey of agencies, and/or (3) questionnaires/interviews targeted to specific agencies.

Examples of applications for automated work zone crash attenuation were found in the literature review for six agencies. The corresponding information is summarized for each agency in the sections below.

The survey discussed in Chapter 3 included questions about automation in work zones. Several agencies indicated in the survey that they had utilized automation in work zones and were willing to be contacted for further information.

From both the literature review and the survey, a total of three agencies were identified that had used ATMA for some type of emergency response. A list of questions was developed, and the contact person from each agency was emailed a description of the project, a request for a short virtual meeting, and the list of questions. In multiple cases, more than one person at an

agency was identified, and each was contacted. The identified contacts were asked to forward the email or notify the research team if someone else at the agency would be in a better position to provide the information. If no response was received, several follow-up emails were sent. In some cases, the agency provided a written response, and in others the information was gathered through a discussion with the agency contact. Responses were gathered from three agencies and are presented in the following sections.

6.2.1 Responses from the Survey

A survey was conducted to gather information about the automated processes that IOOs have implemented or are planning to implement, as described in Chapter 3. Agencies were asked about their use of automated processes in work zones. The most common automated construction process was the use of smart arrow boards, with 45% (n = 14) of agencies noting that they have used the technology and 32% (n = 10) planning to use the technology or evaluate its use in the next 3 to 5 years. The use of automation for construction monitoring was the next most common application (23%, n = 7), with 47% (n = 14) of agencies indicating that they plan to use automation for this application. Around 13% (n = 4) of agencies noted that they were using crash abatement vehicles in work zones, and 43% (n = 13) were planning to use these vehicles. Around 13% (n = 4) of agencies used automated work zone lane closures, with 71% (n = 22) planning to use or evaluate the use of automation for this application in the near future.

6.2.2 California

One study was found in the literature that described the use of automated work zone crash attenuation in California.

Summary of Literature for California

The California Department of Transportation (Caltrans) has developed a pilot ATMA system to ensure the safety of TMA-equipped vehicle drivers. The system includes a leader vehicle and a follower vehicle. The ATMA is attached to the follower vehicle and has its own GPS unit. The system was evaluated at a closed-track facility for 100 hours and performed successfully in 15 performance tests and 11 safety tests. Since the system’s successful performance in these tests, Caltrans has been evaluating its regulations in order to make the system available on public roadways (DRISI 2021).

6.2.3 Colorado

One study was found in the literature that described the use of automated work zone crash attenuation in Colorado.

Summary of Literature for Colorado

The Colorado DOT (CDOT) retrofitted two TMA-equipped vehicles with automated driving system (ADS) technology. The vehicles are used to shadow-paint striping operations in autonomous mode. The lead vehicle is operated by a human driver, and the TMA-equipped vehicle is an autonomous driverless vehicle. The ATMA follows or replicates the lead vehicle’s maneuvers, with the lead vehicle continuously transmitting information such as speed, position, and heading to the follower. The ATMA then replicates the path of the lead vehicle while maintaining a specified gap. The ATMA also has radar and other sensors to detect obstacles and stop the ATMA if needed. The lead vehicle can also stop the ATMA if needed (AASHTO n.d.)

Researchers from Colorado State University carried out a project to understand the interaction between the ATMA system and workers. A survey of 13 DOT workers was conducted regarding their attitudes toward the ATMA system. On the whole, the workers had a positive attitude toward the ATMA because it enhances the safety and reliability of their work. However, it was found that the workers were not comfortable operating the ATMA in complex situations (Miller and Pourfalatoun 2021).

Summary of Conversations with Colorado

Colorado has the most mature ATMA deployment program. A discussion with CDOT (Heather Pickering-Hilgers, Assistant Director of Mobility Technology, Colorado Department of Transportation, November 2023) indicated that it has implemented two ATMAs in rural areas of Colorado. The primary use is for paint stripping. One system has been in use since 2019 and the other since 2021. CDOT was awarded a Strengthening Mobility and Revolutionizing Transportation (SMART) grant that will enable it to deploy a third ATMA in 2023. This ATMA is expected to be utilized for sweeping and crack-sealing operations. CDOT also hopes to develop a toolkit that can be used by other DOTs that are interested in deploying an ATMA. An ATMA used by CDOT is shown in Figure 6-2.

CDOT notes that the main advantages of the ATMA system are the ability to remove the human driver from the TMA-equipped vehicle and to enhance the safety of the traveling public. Another benefit is the ability to better conduct construction and maintenance activities. CDOT is also expecting to document the benefits, including cost savings, community impacts, and performance improvements, through the SMART grant. Because CDOT is currently in the middle of the SMART grant deployment, it was not able to provide any suggestions for implementation at this time. CDOT noted cost and limited use cases as the most significant barriers to deployment but felt that the SMART grant would eliminate those barriers.

CDOT estimated the cost for a turnkey ATMA retrofit to be approximately $450,000, while the cost for leasing an ATMA would be approximately $7,000 per week. It estimated the cost of training to be around $100,000 and the cost of onsite support and other support to be around $70,000. CDOT has had a few components on the ATMA break but did not have a good estimate for ongoing repair costs because the system is new. CDOT estimated $10,000 to $20,000 annually for maintenance.

6.2.4 Florida

One study was found in the literature that described the use of automated work zone crash attenuation in Florida.

Summary of Literature for Florida

The Florida DOT (FDOT) implemented a pilot project to assess the operational and safety performance of an ATMA system when conducting falling weight deflectometer testing on pavements. A safety operator was always present in the follower vehicle, although the actual application would be driverless. The study recommended that the lead vehicle driver be trained in the use of the ATMA system because the follower vehicle is fully dependent on the lead vehicle’s commands. The study also found that the ATMA system does not perform satisfactorily at roundabouts and median U-turns (Agarwal et al. 2021).

6.2.5 Minnesota

Several sources were found in the literature that described the use of automated work zone crash attenuation in Minnesota.

Summary of Literature for Minnesota

MnDOT (2023) tested the use of a MnDOT maintenance vehicle retrofitted with automated technology on a closed course. MnDOT noted that a retrofit kit is available that can convert a fleet vehicle into an autonomous system that includes an on-board computer, a navigation system, actuators, a user interface, and active safety systems. MnDOT conducted a pilot study under the Minnesota Connected and Automated Vehicle (CAV) Challenge, which allowed industry to propose CAV solutions to transportation problems (MnDOT 2023).

The expected benefits included minimizing workers’ exposure to crashes and enabling the driver to assist crews with finishing tasks faster.

6.2.6 Tennessee

One study was found in the literature that described the use of automated work zone crash attenuation in Tennessee.

Summary of Literature for Tennessee

The Tennessee DOT evaluated an ATMA system using 24 testing scenarios such as driving in a straight line, driving in a slalom line, conducting a lane change, following for trash pickup, following for herbicide application, following for pothole patching, reacting to a vehicle intrusion, reacting to a passing vehicle, and detecting cones. According to Tennessee DOT’s study, ATMA is suitable for work zone operations that require continuous movement for longer periods of time, such as installing pavement markings or repainting. The agency felt that ATMA is not as well suited to work zones that require stop-and-go activities, such as pothole patching, weed spraying, or trash pickup (Kohls 2020).

6.2.7 Virginia

One study was found in the literature that described the use of automated work zone crash attenuation in Virginia.

Summary of Literature for Virginia

The Virginia Tech Transportation Institute (VTTI), Virginia DOT, and a vendor developed and tested an ATMA system for short-term work zone areas. The system operated efficiently at a 15 mph speed when dependable GPS was available. The system was tested for object detection, lateral acceleration, lateral accuracy around a curve, and longitudinal accuracy (White et al. 2021).

6.3 Summary of Applications

Six states were found to have piloted ATMA systems. Pilot tests included use of the technology on a closed course or use of autonomous mode with a human driver present.

6.3.1 Advantages and Suggestions

The current applications are pilot programs, so the benefits of ATMA technology have not been fully realized. However, the expected benefits include the following:

• Reduced risk to workers of injury or death from rear-end collisions.
• Drivers freed to assist crews to finish tasks more quickly.
• Protection of the lead vehicle from crashes.
• Ability to maintain an accurate gap between the follower and lead vehicles, which is not possible in a manual system.
• Ability to be steered during an impact to avoid secondary impacts.
• Ability to be retrofitted to an existing vehicle instead of requiring the purchase of a new one, provided that the existing vehicle follows certain design guidelines.

One agency suggested that ATMA systems are well suited for work zone operations that require continuous movement for longer intervals of time, such as repainting or installing pavement markings. Additionally, ATMA was not considered as well suited to work zones that required stop-and-go activities, such as pothole patching, weed spraying, or trash pickup.

6.3.2 Disadvantages

The main disadvantages that have been noted for ATMA systems include the following:

• Some concerns have been noted that passenger vehicles may try to position themselves between the ATMA and the lead vehicle (Kenter 2017).
• Regulations allowing the use of driverless vehicles may not adequately address the technology.

6.3.3 Challenges

The main challenges noted by agencies include that workers are not confident in using the ATMA system in complex situations (e.g., roundabouts, U-turns), proper training is required for workers to enhance their ability to use the ATMA system, and appropriate training is critical for the lead vehicle driver because the overall system is highly dependent on the path of the lead vehicle.

6.3.4 Costs

The ATMA system can be either a new system or a retrofit of an existing vehicle. However, generalizable costs for these scenarios were not available.

6.3.5 Status

The ATMA system is available and has been tested. One vendor was noted as having developed an ATMA system (Kenter 2017). As of 2017, the vendor was looking for a North American partner to demonstrate the technology.