It is no secret that the level of traffic congestion on the nation’s roadways continues to increase. Numerous reports and studies have shown that the steady growth in traffic volume has resulted in ever-growing societal and environmental costs associated with delay, pollution, and driver frustration. Although a seemingly endless stream of methods have been proposed to address these problems, including the construction of new roads, use of advanced transportation http://www.trb.org/publications/nchrp/nchrp_syn_340.pdfmanagement systems, and increasing use of transit and travel demand management programs, each method comes with significant monetary costs and, perhaps more importantly, a significant shift in the way personal transportation is funded and used. The development of new roadways and the conversion of existing ones that can be adapted for different uses at different times of the day has been one method used by transportation agencies to more cost-effectively accommodate the constantly changing needs of highway travel. Convertible roadways encompass a variety of techniques that afford an agency an added measure of flexibility in how and when it responds to the needs for more on-street parking, additional intersection turning lane capacity, and short-term corridor capacity. Originally, the intent of this report was to synthesize information related to convertible lanes. However, owing to the lack of readily accessible information within that topic, the scope of the synthesis was narrowed to primarily cover reversible roadways and lanes, one of the largest and more This report may be accessed by Internet users at well-documented subsets of convertible facilities. Reversible traffic operations are widely regarded as one of the most cost-effective methods to increase the capacity of an existing roadway. The principle of reversible roadways is to configure the lanes of a roadway to match available capacity to the traffic demand. These roadways are particularly effective because they take advantage of the unused capacity in the minor- flow direction lanes to increase the capacity in the major-flow direction, thereby eliminating the need to construct additional lanes. They are most effective when highly unbalanced directional flows are present, such as those that occur during daily peak-period travel times, before and after large events, and during emergency evacuations. The relatively simple concept of reversible flow roadways belies their actual complexity and complicated operational requirements. They can require considerable effort to plan and design, and they often require special control and management strategies to keep traffic moving safely and efficiently. Surprisingly, despite the long history and widespread use of reversible roadways worldwide, there have been few quantitative evaluations and research studies conducted on their performance. There are also a limited number of published guidelines and standards related to their planning, design, operation, control, management, and enforcement. Therefore, most reversible lane systems have been developed and managed based primarily on experience, professional judgment, and empirical observation. The limited availability of standardized and formalized practices has resulted in considerable variation within the practices, philosophies, and policies associated with their use. Furthermore, many of the actual costs and benefits of reversible lane systems remain largely unexplored, which may in turn mean insufficient understanding of their operational and safety effects. (Author/publisher)
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