Identifying Curve Reaction Point Using NDS Data

The object of this research was to use naturalistic driving study data (NDS) to determine where drivers begin reacting to the presence of a curve. Understanding where drivers begin to react to the curve is important for optimal placement of traffic control devices, such as advance curve warning signs, as well as other countermeasures. Time series data were modeled using regression analysis. Results indicate that, depending on radius of curve, drivers begin reacting to the curve 164 to 180 meters (538.1 to 590.6 feet) upstream of the point of curvature. This was compared against sign placement guidelines in the 2009 Manual on Uniform Traffic Control Devices, and it was determined these guidelines are appropriately set based on where drivers actually react to the curve. The analysis found that drivers begin reacting to the curve sooner for curves with larger radii than for curves with smaller radii. Drivers may not be able to gauge the sharpness of the curve, or sight distance issues may be a concern for sharper curves. It should be noted that the model only identified where drivers reacted to the curve. This research question did not attempt to answer whether the reaction point was sufficient for drivers to successfully negotiate the curve. It is also noted that sample sizes are small. Due to resource and data constraints it was not possible to model a large number of drivers over large variation of different curve types. Consequently, the results provide useful information but should be used within the context of the study limitations.