This document presents a synthesis of current information and operating practices related to roadside safety and is developed in metric units. The roadside is defined as that area beyond the traveled way (driving lanes) and the shoulder (if any) of the roadway itself. The focus of this guide is on safety treatments that minimize the likelihood of serious injuries when a driver runs off the road. This guide replaces the 1989 AASHTO "Roadside Design Guide."

Guardrail and median barrier design information is presented which will permit the safest highways consistent with current state-of-the-art barrier technology. Since guardrail and median barrier installations are hazardous in themselves, emphasis is placed on reducing the number of installations to those which can be clearly justified. The design procedure presented involves two steps: (1) determination of points and length of need for the installation, and (2) selection and layout of appropriate guardrail or median barrier system.

Barrier installations are warranted (or justified) only at highway locations where the consequence of an errant vehicle leaving the roadway is judged to be more hazardous than the impact with the barrier installation. A six degree-of-freedom mathematical model was found to be useful in describing dynamic behavior of a vehicle during impact. Predictions of vehicle and barrier behavior correlated with results obtained from full-scale crash tests. Crash conditions simulated with a computer were used to identify and evaluate vehicle static and dynamic as well as barrier parameters. Vehicle weight, yaw mass moment of inertia, and deformation constant were found to be significant.

"The Roadside Design Guide presents a synthesis of current information and operating practices related to roadside safety and is written in dual units-metric and U.S. Customary. This book is a guide. It is not a standard, nor is it a design policy. It is intended to use as a resource document from which individual highway agencies can develop standards and policies. Although much of the material in the guide can be considered universal in its application, several recommendations are subjective in nature and may need modification to fit local conditions. However, it is important that significant deviations from the guide be based on operational experience and objective analysis. The 2011 edition of the AASHTO Roadside Design Guide has been updated to include hardware that has met the evaluation criteria contained in the National Cooperative Highway Research Program (NCHRP) Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features and begins to detail the most current evaluation criteria contained under the Manual for Assessing Safety Hardware, 2009 (MASH). For the most part, roadside hardware tested and accepted under older guidelines that are no longer applicable has not been excluded in this edition." -- AASHTO website.

Various methods of assessing noise, loudness, and noise annoyance are reviewed and explained; sources, types, and intensities of traffic noise are noted; typical means of abatement and attenuation are described; design criteria for various land uses ranging from low-density to industrial are suggested and compared with the results of previous BBN and British systems for predicting annoyance and complaint; and a design guide for predicting traffic noise, capable of being programmed for batch and on-line computer applications, is presented in form suitable for use as a working tool. A flow diagram describes the interrelationships of elements in the traffic noise prediction methodology, and each element is discussed in detail in the text. The text is presented of a tape recording that takes the listener through a series of traffic situations, with such variables as traffic distance, flow velocity, distance, outdoors and indoors, and presence or absence of absorbers and attenuators.