Convertible Roadways and Lanes (2004)

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3 CHAPTER ONE INTRODUCTION BACKGROUND Convertible lanes and roadways encompass a wide variety of facilities on which traffic operations are adjusted at dif- ferent times to adapt to changing traffic conditions. The modifications might require changes to the direction of flow, the types of vehicles permitted in certain lanes, and the types of maneuvers (through, turning, parking) that are allowed. The conversions might take place in a single lane, the entire roadway, or even on the shoulders. Such changes from one use to another may occur periodically throughout the day or on certain days of the week. The changes may also occur on an occasional basis, on a few rare occasions, or during several planned events a year. The manner in which convertible roadways are operated also varies widely. Some roadways have been controlled through noth- ing more than traffic signs, whereas others require complex computer-controlled lane use signals and automated barri- cade systems. Their lengths have been as short as a city block and longer than 100 mi. One simple type of lane conversion takes place nearly unnoticed every day when on-street parking on urban arte- rial roadways is prohibited so that the lane can be used for an extra lane of travel during peak-period travel time. More complex examples of convertible roadways include bridges and tunnels that allocate lanes based on the level of direc- tional traffic demand, freeways that reserve lanes for buses or high-occupancy vehicles (HOV) during certain times of the day, tollbooth approaches that accommodate vehicles from either direction, and intersection approaches that con- vert lanes to serve various directional movements at differ- ent times of the day. Among the most widely applied type of convertible roadways are reversible lane highways. The ITE defines a reversible lane system simply as having an operation in which “one or more lanes are designated for movement one-way during part of the day and in the opposite direc- tion during another part of the day” (ITE 1997). Under cer- tain conditions, a system may even include shoulders or other areas of the roadway cross section that would nor- mally be dedicated to carrying traffic in one direction to accommodate traffic in the opposing direction. The goal of reversible roadways is to provide additional capacity for periodic unbalanced directional traffic demand, while minimizing the total number of lanes on a roadway. One commonly cited example of a multilane reversible highway is a segment of Outer Drive in Chicago, Illinois, in which the eight-lane roadway operates with a 6–2 directional lane split during peak-period travel times. The relatively simple concept of reversible flow road- ways, however, belies their actual complexity and opera- tional requirements. Although widely regarded to be one of the most cost-effective methods for increasing the capacity of an existing roadway, the reversal of traffic flow can re- quire significant investments in traffic control and en- forcement. It can also require considerable effort to plan and design facilities for this use. In addition, if not care- fully planned, designed, and managed, convertible road- ways can be hazardous locations for both vehicular and pe- destrian traffic. OBJECTIVES Despite the long history and widespread use of reversible roadways throughout the world, there have been relatively few quantitative evaluations and research studies con- ducted on their performance. Similarly, there is also a comparatively limited amount of published information available on issues related to their planning, design, op- eration, control, management, and enforcement. There- fore, the majority of reversible lane systems that have been used have been developed and managed based pri- marily on experience, professional judgment, and empiri- cal observation. The limited availability of standardized and formalized practices has also resulted in considerable variation within the practices, philosophies, and policies associated with their use. In turn, many of the actual costs and benefits of reversible lane systems remain largely un- explored and may have even contributed to an increase in traffic accidents, reduced efficiency, and misallocation of resources. The motivation for undertaking this synthesis was to address the need to enhance the understanding within the transportation community relative to convertible and re- versible lane use. Better knowledge of their characteristics and operational requirements, costs, and benefits, may re- sult in the systems’ being more effectively implemented in the future. This synthesis report will provide those seeking to de- velop new, reversible facilities or to improve existing ones, with a single-source document on the current state of the practice and descriptions of operational strategies that are

4 in use or have been used. It also documents the historical development of reversible lanes, their application for vari- ous types of needs, lessons learned from previous imple- mentation, costs and benefits associated with their use, and various techniques and successful practices that have been developed. METHODOLOGY This synthesis was conducted in three main parts. The first, a review of existing literature, covered two separate al- though closely related sources of information. The first were the traditional sources of technical information, in- cluding scientific and practitioner-oriented journals, con- ference compendiums, trade publications, research project reports, and nontechnical reports. This effort was under- taken by using various library search services and the Na- tional Transportation Library’s Transportation Research In- formation Service. The second was a review of the “gray literature,” including unpublished planning studies for local communities; various department of transportation (DOT) reports; law enforcement and emergency management op- erational manuals; and other location-specific, difficult-to- access reports and studies. The second part was a survey of current and recent practice conducted by means of a questionnaire developed primarily to determine the number, location, and nature of reversible lane applications throughout the United States and Canada and, to a lesser extent, overseas. The question- naire was also used to gauge some of the general trends and philosophies that have existed within this traffic man- agement strategy. Both the survey and the literature review were integral to the third and last step of the synthesis, which included field visits and discussions with practitioners where re- verse-flow lanes have been used. These interviews and site visits were a key component of the synthesis effort because they permitted a firsthand review of the facilities and their operations. They also permitted more specific questions to be answered and copies of plans and reports to be obtained. SYNTHESIS ORGANIZATION This synthesis report features seven chapters that describe the history and practices associated with reversible lanes and roadways. Where appropriate, the information is pre- sented in chronological order to illustrate the development of convertible lane use and its associated issues over time. Chapter two summarizes the general concepts and ob- jectives of reversible flow facilities. It includes a brief his- tory of their development and some of the key terms that are associated with their use. Chapter three focuses on the planning and design of reversible facilities. The first half of the chapter pays particular attention to the warrants and criteria for reversible roadways, as well as some of the op- erational policies that often must accompany their use. The second half concentrates on the design aspects of reversible roadways, including the various standards, criteria, and philosophies that have governed the design of new facili- ties, as well as the adaptation of existing nonreversible roadways for reversible operation. The material presented in the design sections includes discussions at both overall system level and local facility level. Chapter four synthe- sizes information related to the management, control, and enforcement of reversible facilities. This chapter includes strategic management and control techniques as well as the application of specific control devices. Particular attention is paid to the primary locations and time periods that are associated with the transition of flow from one direction to the other. Chapter five focuses on the performance assess- ment of reversible roadways, including the determination of their costs and benefits. That chapter synthesizes both the measures of performance and the analytical methods used in assessing the operational and safety aspects. Chap- ter six synthesizes the current state of practice, summariz- ing the results of the survey, and it presents six different applications of reversible flow facilities. The conclusion, chapter seven, summarizes the major findings of the syn- thesis effort as well as some of the lessons learned, exam- ples of successful practices, and needs and suggested areas of future research. The project survey questionnaire is in- cluded in Appendix A, and the results gathered from the survey are summarized in Appendix B.