Missouri Study Indicated That the Leader-Follower Truck Mounted Attenuator (TMA) System Effectively Managed Gap Distance, with an Average Gap Distance Difference between Actual and Desired Being -3.21 Feet for Mobile Work Zones in Kansas City.

Researchers Analyzed Log Data from a Pilot Leader-Follower Automated Truck-Mounted Attenuator System to Determine Its Performance on Metrics Such as Following Distance and Speed.

Date Posted

AMR Leader-Follower System TMA Evaluation

Summary Information

Protecting the safety of work zone workers is a priority for local and state transportation agencies. Advancements in technology, such as automated leader-follower vehicle systems for truck mounted attenuators (Leader-Follower TMA) system, allow for the further separation of the work zone workers from threats to mobile and slow-moving operations, such as lane striping, sweeping, bridge flushing, and pothole repair. This study evaluated MoDOT’s pilot program for Leader-Follower TMA system in the Kansas City and Southwest Districts to identify the feasibility and potential benefits of implementing the system. The evaluation of the TMA system included DOT surveys and interviews from 43 agencies, field study in August 2022 as well as economic analysis.


The field test of this system collected and analyzed 12 hours of data across two deployments on US highways outside of major cities in Missouri, one in the day (Kansas City District) and one in the night (Southwest District). Log files were collected at 20Hz with the important variables being a timestamp, system state, GPS coordinates, navigation state, desired speed, desired gap, actual speed, actual gap, and system notes. Key measures of effectiveness include automatic stops (A-stops), instances of dead reckoning (DR), gap distance, and speed. Video data was also collected from four cameras mounted on the vehicles to identify potential causes of DR. The data were processed separately for the Southwest and Kansas City due to the different desired gap between leader and follower vehicle (700 feet for the Southwest District and 175-200 feet for the Kansas City District). Additionally, a Benefit-Cost Ratio (BCR) analysis was conducted to quantify the benefits and costs of deploying the Leader-Follower TMA system. The estimated benefits were based on data on TMA hits, average crash costs, and follower TMA hit rate, while factored costs include system integration for existing equipment, training, and annual maintenance and support. The analysis assumed upgrading one TMA to Leader-Follower TMA with a life cycle of 10 years.


  • The Leader-Follower TMA system effectively controlled gap distance and speed as per log data. Average gap and speed differences ranged from -3.21 feet to 15.38 feet and -0.006 mph to -0.39 mph, respectively. This indicated that shortening the desired gap distance and software updates could lessen gap discrepancies.
  • The system showed A-stops and DRs, often due to GPS signal loss. A-stops ranged from 0.32 to 1.15 per hour and DRs from 6.06 to 13.61 per hour. This indicated that reducing the desired gap distance and updating software might decrease GPS signal loss instances.
  • The Leader-Follower TMA system primarily helps reduce the number of workers injured, thus reduce injury costs from TMA hits. Economic analysis revealed a total benefit of saving $30,326.24 with a BCR of 0.83. The BCR could potentially reach 1.0 or higher if the system integration cost is reduced to $243,304 (e.g., due to economies of scale with the purchase of additional units). 

A Leader-Follower TMA system which allows the worker to be removed from the follower vehicle.

Figure 1. A Leader-Follower TMA system

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