Review of How to Make Two-Lane Rural Roads Safer: Scientific Background and Guide for Practical Application by R. Lamm, A. Beck, T. Ruscher, T. Mailaender, S. Cafiso, and G. La CavaHow to Make Two-Lane Rural Roads Safer: Scientific Background and Guide for Practical Application

Abstract

This book sheds a new light to the design practice of two-lane rural highways, and provides scientific backgrounds and guides that would help highway engineers design safer two-lane rural highways. The guides presented in this book are based on research studies conducted by the authors and others on the relationships between the elements of the horizontal alignment and accident rates. Often, when accidents take place, driver errors are emphasized. However, the authors argue that some elements of the horizontal alignment the relationship between tangent and curved sections contribute to increased accident potential, and by eliminating or improving poor combinations of tangents and curves, highway designers can help reduce accident potentials. The authors found that almost 60% of highway fatalities occur on two-lane rural highways. About half of these fatalities would occur on curved roadway sections. They found that many of these accidents caused by speed errors may be related to inconsistencies in the horizontal alignment design, which would cause the driver to be surprised by sudden changes in the highway’s characteristics, leading him or her to exceed the critical speed of a curve, hence losing control of the vehicle. The authors concluded that curved roadway sections and the associated transition sections would present a great opportunity for reducing accident frequency and severity. Hence, reducing accidents caused by excessive speeds inconsistent with highway conditions or geometry became the core principle of the methods presented in this book. To unify the analysis of the three consistency criteria discussed below , the authors defined a curvature change rate of the single curve with transition curves CCRS to be used as a parameter to evaluate the safety of transition from a tangent segment to a curve segment of a highway. The accident rate used in this analysis relates the number of accidents that occur on an investigated section in a given time period to vehicle-kilometers traveled on the section. They found that there was a statistically significant correlation between horizontal alignment design expressed by CCRS and safety expressed by the accident rate . Using these two factors, the authors classified the horizontal alignment design into three design classes: good, fair, and poor design. In Chapters 1 and 2, the authors present three quantitative safety criteria which, when properly applied, are intended to provide rural two-lane highways with design consistency, operating speed consistency, and driving dynamic consistency and help improve the highway designer’s ability to analyze two-lane rural roads, thus providing safer designs. These criteria are summarized below for the prospective readers. These are the main concepts