Highways provide the predominant mode of transportation in the United States and much of the world. The highway system in the United States consists of over 3,900,000 miles of public roads and streets, of which 3,100,000 miles are rural roads,' Highway traffic consists of a vast fleet of personal vehicles for transporting individuals and small groups, and commercial vehicles for transporting freight and larger groups of passengers. Vehicle ownership in the United States is the highest in the world. The national average is 0.56 passenger cars per capita? Each year 52,000 deaths and over 4,000,000 injuries occur on roadways within the United States and Canada.3 Features such as increased sight distance, increased lane widths, widened clear zones along the roadway, and wider, higher-type shoulders have been added to highway facilities in the United States to improve safety for the travelling public. These improvements work extremely well to provide adequate time for the driver to perceive approaching roadway conditions and/or to recover from an errant movement. However, in order to be effective, proper maintenance of such improvements is imperative. One safety feature, the roadway shoulder, has been recognized as desirable ever since engineers began paving our roadways. However, the width, uniformity, and stability of roadway shoulders has varied greatly from roadway to roadway and along different sections of the same roadway. Roadway safety standards have required that improvements be made in the integrity of the shoulder. This has been achieved by using construction materials that provide a more stable shoulder and by using a wider shoulder width, as shown in Figure 1. Also, shoulders are usually required along modern roadway pavement edges to provide a safer travel way for the motoring public. "A shoulder is the portion of the roadway contiguous with the traveled way for accommodation of stopped vehicles, for emergency use, and for lateral support of the sub-base, base, and surface courses. It varies in width from only 2 feet or so on minor rural roads, ...to about 12 feet on major roads.", Shoulders may be paved with concrete or asphalt, or stabilized with granular or other materials and/or sodded. Unfortunately, roadways are often resurfaced without restoring the adjacent shoulders to bring them up to the resurfaced roadway level (see Figure 2). This condition can lead to vehicle tires dropping off of the pavement edge, and, subsequently, to an accident. In fact, a study by Ivey and Griffin ranked pavement edge-shoulder drop-off among the top accident-related pavement disturbances.' The purposes of this report are to: • identify the scope of work in resurfacing contracts which can lead to such drop-offs; • identify the magnitude of contract work creating such drop-offs; and • recommend changes in contract scope or performance to eliminate or mitigate such occurrences. Conditions where the existing roadway cross sections have side slopes which drop directly from the travel lane into a side ditch were not addressed in this study. These types of roadway do not have an existing shoulder. Additionally, this study was confined to two-lane rural roadways within the United States, although some recommendations are also valid for multi-lane facilities. (Author/publisher)
Abstract