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Appendix II.—TRAFFIC DETERMINANTS OF INTERSTATE HIGHWAY STANDARDS

Highways are avenues of transportation. Within limits of feasibility they should be adjusted in the various elements of their design to the justifiable needs of traffic. Failure to effect such adjustments in highways previously built, because of a deficiency of traffic information and knowledge of road-traffic relationships, have been the cause of much of the present highway obsolescence.

This bridge on U S Route 30 in Pennsylvania, designed for about H20 loading, is strong enough to carry infrequent loads as heavy as the 152,000-pound tank transporter and tank. For adequacy, the bridge should be wider than the approach pavements.

Significant advance has been made in the last 10 years in the development of improved highway design standards as a direct result of more exact information concerning road usage, motor-vehicle performance, and driver behavior in the presence of various traffic conditions and roadway characteristics. This information is used as a

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