Public Roads: A Journal of Highway Research, Vol. 25, No. 7

Barber, E.S.; Willis, E.A.; Benkelman, A.C.; Olmstead, F.R.; Timms, A.G.; Grieb, W.E.; Werner, George; Dimmick, Thomas B.; Kipp, Mary E.; Meadows, R.W.; McCallum, W.R.; Lewis, R.H.; Halstead, W.J.; Jackson, F.H.; Allen, Harold; Goodall, David M.; Welborn, J.Y.; St. Clair, G.P.; Clark, Sidney B.; Wintermyer, A.M.; Pauls, J.T.; Goode, J.F.; Woolf, D.O.; Smith, T.R.; Farrell, Fred B.; MacDonald, Thos. H.; Cope, E.M.; Liston, L.L.; Levin, David R.; Markham, Marion G.; Paterick, Henry R.; Lancaster, R.J.; Driscoll, J.E.; Rex, H.M.; Normann, O.K.; Walker, W.P.; Lynch, John T. · 1949 · ROSA P / United States. Government Printing Office

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Summary

This 1949 article, published in *Public Roads* as the Second David Beecroft Memorial Lecture, addresses the critical need to align highway geometric design with actual driver behavior to improve safety. The author, Thomas H. MacDonald, argues that existing highway systems, largely built under cost-saving pressures in the previous three decades, are inadequate for modern traffic volumes and characteristics. The central thesis is that driver behavior *en masse* is the key determinant for safe highway design, and that current infrastructure fails to accommodate the dynamic nature of motor vehicles, leading to preventable accidents and inefficiencies. The paper synthesizes findings from extensive traffic research conducted by the Public Roads Administration, including observations of driver spacing, speed, and reaction times. It analyzes data on vehicle registrations, fatality rates, and the impact of commercial vehicles on road capacity. The study highlights specific design flaws, such as narrow lane widths, insufficient sight distances, and the lack of adequate shoulders. It also examines the safety records of controlled-access highways, such as the Pentagon network and the Metropolitan New York Parkway System, which demonstrated significantly lower fatality rates due to the elimination of traffic conflicts. Key findings indicate that undercapacity is the primary hazard on existing highways. The paper establishes specific design standards based on observed driver behavior: rural two-lane highways should maintain sight distances of 1,500 to 2,000 feet for at least 60% of their length to safely accommodate peak traffic. Lane widths of 12 feet are recommended for main highways carrying commercial traffic, as narrower lanes reduce capacity and safety. The research emphasizes the critical role of shoulders, noting that adequate paved shoulders prevent capacity loss from disabled vehicles and provide refuge for pedestrians. Furthermore, the study reveals that average time spacing between vehicles is often dangerously short, with many drivers following at intervals that do not allow for safe reaction times. The data shows that multilane divided highways can accommodate three to six times more vehicles per lane than two-lane roads with greater safety. The significance of this work lies in its call for a paradigm shift in highway engineering from cost-per-mile metrics to total cost-of-transportation analysis. MacDonald concludes that designing for safety is economically justified when considering the costs of accidents, lost time, and vehicle operation. The paper advocates for a long-term rehabilitation program to upgrade highways to liberal standards, emphasizing that safe design does not increase initial construction costs but reduces total societal costs. It also stresses the importance of integrating highway design with driver education and enforcement, arguing that mastery of highway safety requires coordinated efforts across vehicle design, traffic laws, and infrastructure.

Key finding

Highways designed with controlled access and liberal geometric standards, such as the Pentagon network and New York Parkway System, achieve fatality rates of 1.5 to 3.9 per 100 million vehicle-miles, which is one-fifth to one-third of the national average.

Methodology

review

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• Empirical Findings: observational prevalence