Updated Model for Advance Placement of Turn and Curve Warning Signs

Warning signs are used to warn road users of potential hazards located in or near a roadway. A properly placed warning sign provides the road user with adequate time to select and execute the proper response. Table 2C-4 in the 2009 edition of the Manual on Uniform Traffic Control Devices presents recommended advance placement distances for warning signs on the basis of the approach speed and the appropriate speed at which to negotiate through the hazard. These placement distances are determined through use of the AASHTO stopping distance equation with assumptions for reaction, deceleration, and sign legibility distances. A recent NCHRP study measured continuous driver deceleration on the approach to and through a change in horizontal alignment. The findings from that research were combined with more appropriate selections of response time and legibility distances to develop improved recommendations for the advance placement of warning signs on the approach to a change in horizontal alignment. With the use of these new assumptions, a new table was created on advance placement distances for warning signs placed in advance of changes in horizontal alignment. The table indicates that the advance placement is similar to the current values when speeds are 50 mph and lower. For higher speeds, the warning signs should be placed up to 75 ft farther from the start of the alignment change than when the advisory speed is low. The signs can be placed up to 100 ft closer to the start of the alignment change when the advisory speed is within 20 mph of the approach speed.