Objective: To test the effectiveness of the FHWA guidelines for intersection design.
Methods: In an experimental design we used kinematics measures from an instrumented vehicle and behavioral (error) data collected during on-road evaluations to quantify the effects of improved versus unimproved intersections (turn phase) and to determine if these intersections were safer (vehicular stability and driver confidence) for both older (65-85 years) and younger (25 -45) drivers. We analyzed kinematics data with a 2 x 2 repeated measures ANOVA and behavioral data (driving errors yes, no) with Wilcoxon sign rank test (within subject variable: intersection improved vs. unimproved) and Wilcoxon rank sum test (between subject variable: age, younger vs. older driver).
Results: Kinematics measures (turn phase), showed three maneuvers had statistically significantly lesser side forces (measured by lateral acceleration and combined acceleration) for the improved conditions, and four maneuvers had statistically significantly greater, yet appropriate, speeds for the improved conditions. Lesser side forces indicated improved lateral stability and increased speed indicated greater confidence. Drivers made fewer errors on two of the improved intersections; but across all maneuvers, older drivers appeared to make fewer errors on the improved intersections.
Conclusions: This study brings empirical intersection design and safety information for engineers and city planners to consider as they plan and develop intersections. Future researchers may want to use the conceptual and analytical framework of this study to determine the effectiveness of other FHWA guidelines. Given that these intersection design guidelines benefit younger and older drivers alike, plausible policy-making opportunities are opened in the design of safe roadway systems, to benefit the broad spectrum of adult drivers.