Fluorescent retroreflective signing of work zones : abstract

Fluorescent retroreflective materials increase the brightness of traffic signs. In construction work zones a benefit is expected from the increased conspicuity of fluorescent retroreflective signs. Fluorescent material can be used instead of non-fluorescent materials both for the advance warning signs that indicate the configuration of the upcoming work zone and for additional backing boards behind traffic signs, e.g. to attract attention to a posted speed limit sign. In a field experiment at a construction work zone on a motorway, conspicuity measurements during daytime showed that fluorescent retroreflective material doubled the conspicuity with respect to non-fluorescent material, corresponding to a daytime luminance which was twice as high.
Driver behaviour in the approach area of a construction work zone was observed via video recordings during dusk, daylight and nighttime conditions. On consecutive days, three types of signing were installed in the approach area of the work zone: non-fluorescent signing (High Intensity Grade (HIG)), fluorescent signing (Diamond Grade (DG)) and the combination of fluorescent signing and backing boards (DG+BB). Driver behaviour was analysed in terms of speed (average speeds and percentage of vehicles entering the work zone at excessive speeds), Time-To-Collision (TTC), and lane changes.
Results showed that fluorescent retroreflective material reduced the (very high) speeds during dusk conditions (especially during low ambient light conditions, fluorescent materials have a very bright appearance). At night, speeds increased with fluorescent signing. Backing boards behind the posted speed signs reduced average speeds and excessive speeds at the entry of the work zone during daytime. Without fluorescent backing boards more than 25% of the cars drove faster than 100 km/h during daylight at the work zone entry, while with fluorescent backing boards only 10% drove that fast. With respect to the interaction between vehicles, a decrease of the proportion of small TTCs during night showed that DG and DG+BB signing caused a shift into a safer direction, even though a speed increase was recorded at night in the condition with DG signing. Furthermore, during dusk and night, fluorescent backing boards reduced last minute lane changes. In daylight the opposite was found.