In 2006, there were approximately 23,500 rear-end crashes involving heavy trucks (i.e., gross vehicle weight greater than 4,536 kg). The Enhanced Rear Signaling (ERS) for Heavy Trucks project was developed by the Federal Motor Carrier Safety Administration (FMCSA) to investigate methods to reduce or mitigate those crashes where a heavy truck has been struck from behind by another vehicle. Visual warnings have been shown to be effective, assuming the following driver is looking directly at the warning display or has his/her eyes drawn to it. A visual warning can be placed where it is needed and it can be designed so that its meaning is nearly unambiguous. FMCSA contracted with the Virginia Tech Transportation Institute (VTTI) to investigate potential benefit of additional rear warning-light configurations as rear-end crash countermeasures for heavy trucks. This paper will describe the dynamic closed-track testing performed and overall countermeasure performance of two rear warning-light configurations as compared to the baseline brake lights. The key metric of effective performance was the rear warning-light configurations' ability to draw the following-vehicle driver's eye forward during an in-vehicle distraction task. Thirty participants were coached to maintain a following distance of approximately 120 ft (36.58 m) during multiple closed-track loops. Results indicated a strong trend for improved eye-drawing performance of both rear warning-light configurations over that of normal brake lights. The rear warning-light configurations had significantly better attention-getting ratings, as compared to baseline brake lights, while the participants were fixating either directly ahead or 30 deg off-axis. Participants gave discomfort glare ratings while (1) positioned directly behind the test trailer and fixating on the vehicles rear-lighting (i.e., acting as a following vehicle) and (2) positioned in the adjacent lane and looking past the rear-lighting (i.e., acting as a passing vehicle). The results indicated that there were no significant differences in discomfort glare ratings for the two rear warning-light configurations and brake lights. The helpfulness and usefulness ratings showed that overall participants perceived both rear warning-light configurations positively. In conclusion, both rear warning-light configurations appear to be good candidates to move forward to the follow-on real-world data collection effort.