Evaluation Of The 13 Controlling Criteria For Geometric Design

"TRB's National Cooperative Highway Research Program (NCHRP) Report 783: Evaluation of the 13 Controlling Criteria for Geometric Design describes the impact of the controlling roadway design criteria on safety and operations for urban and rural roads."--Publisher description.

TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 417: Geometric Design Practices for Resurfacing, Restoration, and Rehabilitation documents the current state-of-the-practice related to nonfreeway resurfacing, restoration, and rehabilitation projects.

At head of title: National Cooperative Highway Research Program.

The American Association of State Highway and Transportation Officials (AASHTO) publication titled "A Policy on Geometric Design of Highways and Streets" (Green Book) provides guidance to the designer by referencing a recommended range of values for critical dimensions for the design of highway facilities. For various reasons, it may be necessary to design a section of highway with substandard values for some elements. Such design exceptions require appropriate assessment and justification of the potential impacts to highway safety and operations. This study was performed to develop a guideline for design exceptions. The guideline for development and evaluation of design exception projects was developed and presented. The guideline outlines the steps for developing and evaluating design exception projects. The potential impacts of design exception elements to highway safety and operations are listed for the 13 controlling criteria to provide designers with important and easy to use information. The possible counter measures for each of the controlling criteria are listed in a one-page table for easy reference. The proposed safety evaluation process was presented in terms of safety impacts of individual substandard elements as well as the combined impacts of the substandard elements. An Excel based computer program was developed for life-cycle benefit-cost analysis of design exception projects. A decision on design exceptions can thus be made rationally with the recommended guideline and methods.

The importance of proper geometric dimensioning and tolerancing as a means of expressing the designer's functional intent and controlling the inevitable geometric and dimensional variations of mechanical parts and assemblies, is becoming well recognized. The research efforts and innovations in the field of tolerancing design, the development of supporting tools, techniques and algorithms, and the significant advances in computing software and hardware all have contributed to its recognition as a viable area of serious scholarly contributions. The field of tolerancing design is successfully making the transition to maturity where deeper insights and sound theories are being developed to offer explanations, and reliable implementations are introduced to provide solutions. Machine designers realized very early that manufacturing processes do not produce the nominal dimensions of designed parts. The notion of associating a lower and an upper limit, referred to as tolerances, with each dimen sion was introduced. Tolerances were specified to ensure the proper function of mating features. Fits of mating features included clearances, location fits, and interference fits, with various sub-grades in each category assigned a tolerance value depending on the nominal size of the mating features. During the inspection process, a part is rejected if a dimension fell outside the specified range. As the accuracy requirements in assemblies became tighter, designers had to consider other critical dimensions and allocate tolerances to them in order to ensure the assembly's functionality.

TRB's National Cooperative Highway Research Program (NCHRP) Report 672: Roundabouts: An Informational Guide - Second Edition explores the planning, design, construction, maintenance, and operation of roundabouts. The report also addresses issues that may be useful in helping to explain the trade-offs associated with roundabouts. This report updates the U.S. Federal Highway Administration's Roundabouts: An Informational Guide, based on experience gained in the United States since that guide was published in 2000.