Traffic congestion and abrupt speed variations in tunnels increase crash risks and reduce traffic operational efficiency. Thus, a pacemaker system (PMS) was developed to stabilize traffic flow by guiding drivers to maintain uniform speeds through the use of sequentially illuminated LED lights installed along tunnel walls. This study aims to quantitatively evaluate the effects of a PMS on traffic operational efficiency and safety in the Geumnam Tunnel of the Seoul–Yangyang Expressway via a driving simulation. In speed-recovery scenarios, sequential LED lights effectively encouraged drivers to gradually restore their speed. Consequently, the average speed increased significantly, whereas both the difference in speed and the space-varying volatility of speed decreased, thus indicating enhanced driving consistency and improved flow stability. In speed-reduction scenarios, drivers’ deceleration responses were compared under three PMS operational types: flashing yellow, message display, and combined flashing with a message. Combined flashing with a message yielded the most controlled and pronounced deceleration, thus facilitating drivers in reducing their speed smoothly without abrupt braking or instability. The results collectively demonstrate that a PMS can serve a dual function by supporting both speed recovery under normal conditions and safe deceleration in accident cases. These findings provide empirical evidence of the effectiveness of a PMS as an intelligent tunnel-traffic management system and highlight its potential as a proactive safety technology. Furthermore, this study offers practical insights for future PMS designs as well as operational guidelines for enhancing traffic efficiency and driver safety in tunnel environments.

Traffic congestion in tunnels, particularly phantom jams, significantly reduces driving efficiency and increases crash risks. To address this issue, a Pacemaker System (PMS) was implemented in the Geumnam Tunnel along the Seoul–Yangyang Expressway. A PMS aims to stabilize traffic flow and improve operational efficiency by guiding drivers to maintain uniform speeds through sequential LED illumination. This study aims to quantitatively evaluate the effectiveness of a PMS on traffic flow by analyzing Vehicle Detection System (VDS) data collected before and after its implementation. The analysis incorporated Level of Service (LOS) categories A–E, and distinguished between peak and non-peak hours to assess speed improvements and flow stabilization. The results indicated that the PMS increased the average speeds by approximately 6.5% across the LOS A–E conditions, with the most pronounced effects observed in LOS C–E. Furthermore, the speed distribution analysis revealed that the PMS enhanced lower-percentile speeds and reduced speed variance, thereby contributing to improved traffic stability. Statistical tests confirmed that the observed improvements were significant (p < 0.05). These findings demonstrate that the PMS effectively mitigates phantom jams and improves tunnel traffic efficiency, offering empirical evidence to support future PMS deployment and the development of tunnel traffic management policies.