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 was that sight distances were frequently too short for passing. The AASHO policy sought to overcome this deficiency in future construction by furnishing derived values for needed passing sight distances on three-lane roads. “Desirable minimum” values ranged from 900 feet for 50 m.p.h. to 1,700 feet for 70 m.p.h. Another reason for the poor accident experience on three-lane roads was the lack of uniformity and the haphazard manner in which they were marked to regulate overtaking and passing during the early years of their use. A recognized need for improvement in this department led to development of the next of the several policies.

Kentucky’s Daniel Boone Parkway exhibits modern design features such as sweeping curves with adequate sight distances and gentle grades.

A Policy on Criteria for Marking and Signing No-Passing Zones on Two- and Three-Lane Roads, 1940—advocated a uniform system of marking two- and three-lane roads to restrict passing where sight distances were less than certain values as listed for various design speeds. The types of stripes and signs for marking no-passing zones were the province of another AASHO committee, but the recommendations of that committee were included in the policy. Since this feature was more closely related to operation than design, this subject received no further attention by the Committee on Planning and Design Policies but, instead, was handled thereafter by the National Joint Committee on Uniform Traffic Control Devices. 392