AASHTO GD 2nd Edition, January 1, 1965
A Policy on Geometric Design of Rural Highways
Additional Comments: W/D S/S BY AASHTO GDHS * NO LONGER AVAIL.
The art of modern road building is the result of gradual development to meet changing traffic needs and broadened knowledge gained through experience and research. In geometric design—design of the visible features of a road—early practice relied heavily on field location to provide a suitable road to meet standards for alinement, gradient, and other features at minimum cost. Prime recognition was given the cost of various elements of construction and availability of materials. This procedure was satisfactory for the needs of traffic at the time. Few could foresee the tremendous growth in motor vehicle transportation, and even if they could have foreseen it highway engineers could have done little about the additional requirements. The limited funds rightly were devoted to increasing the mileage of improved roads.
Greater numbers of vehicles, changes in their characteristics, a growing knowledge of driver behavior, particularly in the presence of other drivers, and increase in the number of accidents brought into prominence the geometric design of highways to provide maximum service with minimum hazard at reasonable cost. Increased knowledge in other phases of design and improvements in construction equipment, techniques, and materiais made it economically feasible to provide facilities with standards considered too costly before then. The relation of location and design to costs, physical conditions, and fund availability will ever be important in highway engineering, but attention must be given to location and design to fit future traffic needs. A complete highway incorporates not only safety, utility and economy, but beauty as well. Care should be used in the selection of location and geometric elements so that the highway will be beautiful in appearance, compatible with its environment and give vehicle occupants pleasing views from the highway. This policy develops the guide values and details for geometric design which best fit the requirements of motor vehicles as they are constructed and operated currently, and insofar as it is possible to foresee, as they will be in the future.
Safe and efficient highway transportation requires increasing attention to enforcement and driver education as well as to engineering. Our highways necessarily involve conditions wherein drivers singly or collectively must accept regulations and conform with established operational patterns for their mutual benefit. The role of enforcement officials in this regard directly supplements that of the engineer in the design, construction, and operation of the highway. Effective training has demonstrated that proper driver attitude is a major item in enforcement which can be attained through organized effort toward education of all drivers. Discussion of enforcement and education features are not included herein, but it should be recognized throughout that they are essential supplements to engineering.
This Policy is limited to the geometric features of highway design as distinguished from structural design. It is intended as a comprehensive treatise on the geometric design of rural highways and encompasses practically all general controls and features, except those specifically related to urban conditions. The Policy on Arterial Highways in Urban Areas covers the details of urban design only, with reference to this volume for general guides and controls.