PURPOSES : LED based Variable Message Signs(VMS) have been widely used to inform safety messages to the drivers in advance. Legibility Distance of VMS is the most important factor to provide the safety messages to drivers in timely and effective way. However, current National Standards on legibility distance design considers letter size only even there is a difficulty to read the signs at adverse weather conditions such as heavy fog. So, this study examined the legibility issue under fog by evaluating the legibility distance with two design factors such as letter size and luminance. METHODS : Two foggy weather conditions, intermediate and heavy fog, were simulated at real-road-scale Proving Ground. Legibility distance at daytime and nighttime was evaluated by test subjects. Subjects were asked to fill the legible distance on the test sheet and statistical significant was analysed at the lab. RESULTS : The legibility distance(LD) under fog was observed only 22 to 41% of LD observed under normal weather condition at daytime, and 26 to 45% at nighttime condition. Study results showed a consistent increase in LD with higher luminance even at same letter size and vice versa conditions, However, statically significant difference between groups was only revealed when both letter size and luminance level increased conditions. In order to apply the test results in terms of engineering benefits, LD results from significantly different groups was evaluated with relative to Stopping Sight Distance(SSD) within conceptual frame suggested in this study. CONCLUSIONS : From the study results, current National Standard on legibility distance design needs to consider letter size and luminance simultaneously to response the legibility issue in adverse weather conditions.

PURPOSES : This study aims to investigate the effect of the propagation time of variable message sign (VMS) information and drivers’ detour rate on the VMS performance under non-recurrent traffic states. METHODS: A microscopic simulation model (i.e., VISSIM and VISSIM COM User Interface) was developed at a location where VMS messages were most frequently displaced in 2018 from the Busan Regional Construction and Management Administration. The non-recurrent traffic states realized in this study were one- and two-lane close cases with scenarios involving multiple propagation times from 0 min to 20 min in 2 min increments and detour rates from 0% to 50%, in 10% increments. The measures of effectiveness are the average delay per vehicle, total travel time, and reduction rate of the total travel time based on the average value of 30 multiple simulation runs for individual scenarios. RESULTS:For the one- and two-lane close cases, the reduction rate of the total travel time increased as the propagation time shortened and the detour rate became bigger. The optimal (i.e., 0 min propagation time and 50% detour rate) and worst (i.e., 20 min propagation time and 10% detour rate) scenarios produced 41.1% (8.9 h) and 6.4% (1.4 h) and 26.4% (86.5 h) and 1.4% (4.7 h) of the total travel time for the one- and twolane close cases, respectively. CONCLUSIONS : The study results implied that the late propagation time and the low detour rate might not significantly influence the VMS system. Therefore, it is important to improve the information process time for the shorter propagation time and the reliability of the VMS information for a higher detour rate, which will result in a better VMS system performance.