A light rail transit (LRT) system is one of the critical infrastructures in an urban city. Because of right-of-way type C in LRT operations, construction work zones of LRT systems are generally located on the city roadway. This kind of construction work typically requires road closures, potentially resulting in traffic congestion and arousing public resentment from original residents. Traffic vehicular impacts from work zones of LRT systems are dynamic depending on the scales and schedules of work zones. Understanding the traffic impacts during the construction works of LRT systems is essential to managing traffic situations and controlling construction schedules. This research explores the traffic impacts near the work zones of LRT systems; a before-and-after comparison method framework based on the Mann–Whitney (M-W) U test is proposed to analyze traffic volume data. The M-W U test is a non-parametric statistical test. One advantage is that it does not require the population for assumptions. This method is suitable for evaluating the difference between two sets of traffic observations without assuming a specific distribution in traffic flow dynamics. The M-W U test is provided to investigate the real traffic data in the ongoing LRT construction case. The results reveal that traffic volume impacts will vary depending on the periods, the locations, and the vehicle types before and under construction works.