Evaluating Driver Response to Bridge Deck Warning Systems During Winter Weather Conditions

Warning signs are often deployed at bridge overpasses during winter to warn motorists of potentially icy surface conditions on the bridge, although the effectiveness of these signs is questionable. One potential improvement to the standard signage methods is the bridge deck warning system (BDWS), which activates a flashing warning sign border or beacon when conditions warrant based on real-time weather and bridge surface data. However, BDWSs have not been broadly implemented in the United States, and consequently, their effectiveness as a safety countermeasure is not well established. To address this knowledge gap, a series of winter field evaluations were performed along three freeway bridge overpasses in Michigan to assess the effectiveness of various BDWS strategies as a speed reduction countermeasure for motorists approaching a potentially icy bridge. The results showed that a BDWS with a flashing light emitting diode (LED) border reduced motorist speeds when encountering a bridge during winter weather conditions compared with the standard “Bridge Ices Before Road” warning sign. The speed reduction effect was consistent between passenger cars and heavy trucks, but was somewhat stronger at night compared with daytime. Greater speed reductions were observed when the BDWS sign was combined with a dynamic speed feedback sign (DSFS) that displayed a “Slow Down” or “Icy Road” message to approaching motorists, with the strongest effects observed when the DSFS message was pulsed between high and low brightness intensities. BDWSs that included only a flashing overhead beacon did not have a significant effect on speeds compared with the standard warning sign.