Background: Studying the effects of traffic vibration on adjacent structures has produced fruitful results, but there is a lack of systematic research on the protection, assessment, and ambient vibration effects on cultural relics, and the majority of the studies focus on above-ground buildings, with less research conducted on underground cultural relic sites. Objective: In order to investigate the effects of road-traffic-induced vibration on nearby underground sites, the distance between them was precisely determined. Methodology/approach: The site of Chengshang Village in Jurong City, Nanjing, China, was chosen as the research object, and the vibration of the underground site caused by traffic volume was measured on-site. Based on statistical analysis of experimental data, the vibration velocity was deduced as a function of the vehicle’s speed and the vibration source’s distance. Results: The excellent frequency band for traffic load vibration is between 0 and 40 Hz, and the attenuation speed of high-frequency vibration is faster than that of low-frequency vibration; the vibration speed is positively correlated with the speed of the vehicle, and the distance from the vibration source is exponentially attenuated; and under the condition of the determined limit value of the load and the vibration speed, the safety distance increases. Conclusions: This research utilizes the collected data to describe the relationship between the vibration velocity and the distance from the vibration source. Additionally, it estimates the appropriate distance at which cultural relics should be placed from the road to ensure their safety. The study’s findings may serve as a valuable point of reference for traffic planning and the preservation of underground cultural monuments.