Page:America's Highways 1776–1976.djvu/350

 The general advantages of pavement markings were recognized after their first use in 1911, and they were included in the early manuals to some extent. However, it was not until 1947 that the effectiveness of centerlines, particularly on two-lane, two-way roads, was confirmed through research. The result of studies at 12 locations in seven States showed that centerline markings provided a general improvement in the transverse positioning of vehicles, that vehicles were driven closer to their proper position on the roadway, and that they encroached on the left lane much less frequently where there was a centerline.

Edge lines were added as a standard device in the current Manual on Uniform Traffic Control Devices for Streets and Highways (1971) and are in universal use. Their effectiveness was determined through a comprehensive study of driver behavior as related to pavement edge markings, conducted by BPR in 1957 in Louisiana and the western States. This study showed that edge lines were very effective aids in confining traffic in the normal travel lane and in reducing partial shoulder use.

By the late 1950’s a substantial number of freeways had been developed in most of our larger cities. As a result of increasing traffic on them, peak-hour congestion became a major problem. Research studies showed congestion during the morning and evening peak travel periods could be greatly reduced by the use of traffic surveillance and addition of further controls. The application of the latest developments in electronic and other technological equipment served to increase operational efficiency and safety.

The Bureau of Public Roads, in cooperation with a number of State highway departments, spearheaded the research and development in this area and has promoted the practical results of its studies. The first project was initiated in 1960 on John C. Lodge Freeway in Detroit. The second one was initiated in 1961 on the Eisenhower Expressway in Chicago and the third in 1964 on the Gulf Freeway in Houston, Texas. After 1965, a large number of States started installing freeway surveillance and control systems, the most extensive of which was the 42-mile loop pilot project in Los Angeles.

Demonstration moving merge control systems have been used since about 1969 on freeway entrance ramps to help ramp drivers enter a freeway in situations where it would be difficult to determine adequate gaps in the freeway traffic. This is an artist’s concept of the moving greenband system, just one type under consideration.

In the late 1960’s, Public Roads continued to expand and refine the technology of freeway operations by undertaking a major travel corridor control investigation in Dallas. This research was a major effort to explore the total corridor concept, including the freeway, service road, arterial street, and surrounding system. Public transportation, bus operations, roadside communications and park-and-ride were modern-day additions to the effort. Public Roads sponsored many other freeway operations studies, among them the improved control of diamond interchanges.

The concepts of integrated surveillance and control are equally important to urban nonfreeway systems. Traffic signals, intersections, and individual aspects have been mentioned. In the late 1960’s, Public Roads stimulated and assisted in “systems” approaches to control traffic for the whole of a certain urban area. One significant output has been the computerized concept of arterial traffic control. Another major project was an urban traffic control research laboratory operating on certain streets in Washington, D.C., which was still active in 1975. This study has had many influences in the broad area of “software” for urban systems, ranging from preprogramed to instantaneous timing. Another major component was an integrated bus priority system. As meaningful results from these studies have become available, nearly all of the States have applied the new technology to other locations.

During the late 1930’s when driver behavior, highway capacity, and traffic control were under intensive study, considerable research was devoted to the effect of highway lighting on traffic operations and safety. For several years prior to this time, illuminating engineers had studied means of reducing nighttime accidents, which were proportionally higher thenthan [sic] those in the daytime. There were only a few hundred miles of rural highways that were lighted, many of which were temporary installations to demonstrate and experiment with the safety aspects of lighting.

In 1939, the Public Roads Administration and the Ohio Department of Highways concentrated their research efforts on the effect of lighting on the lateral position, passing practices, headways, and speeds of vehicles on rural highways. The results showed that the behavior of drivers operating at night without overhead light differed measurably from that in daytime, but that under artificial light they conformed very nearly to their behavior in the daytime. This indicated the advantage of highway lighting for certain speed-volume-geometric highway conditions. 344