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7 CHAPTER ONE INTRODUCTION PROBLEM STATEMENT including technology characteristics and standards and guide- lines for use; (2) notable experiences from historical IPM Various types of illuminated, active, in-pavement marker system applications; and (3) detailed experiences from more (IPM) systems are emerging that offer a range of designs and recent IPM system applications, including system and facility functional features intended to warn, guide, regulate, or pro- characteristics, operation modes, installation and construc- vide illumination for road users. Compared with traditional tion methods, maintenance requirements, system costs, and retroreflective pavement markers (RRPMs), IPM systems can perceived and measured effectiveness. provide a greater level of information to the road user through the use of various marker color changes to indicate regulatory Assimilated in this synthesis report, this information will action (e.g., markers show red illumination when vehicles are help to accelerate successful applications and focus future re- required to stop), flash rates indicative of the level of hazard, search of IPM systems. or "chase" sequences directing the road user to reduce or increase speeds. These systems also offer the potential for increased visibility over traditional RRPMs, particularly METHODOLOGY through horizontal curves. RRPM systems function by re- flecting light from a vehicle's headlights. Hence, the entire Information to support this synthesis effort came from three extent of some horizontal curves cannot be illuminated by primary sources: RRPMs. On the other hand, IPM markers can be designed to provide illumination from a wider range of viewing angles; A review of published literature, giving a more consistent, complete, and clear indication of A formal survey of transportation practitioners, and road curvature. For this synthesis effort, IPM systems also An informal survey of IPM system vendors and users. include lighted devices that are not "in-pavement" but are mounted on concrete barriers or sign posts. Supplemental information was also provided by various NCHRP Synthesis Topic Panel members and through infor- Historically, IPM system use was limited to airport runway/ mal interviews with traffic engineers, researchers, and other taxiway or pedestrian crosswalk applications. More recently, industry professionals. IPM systems have been used to: (1) enhance warning through school and construction zones, at highwayrail crossings, at Literature Review horizontal curves, and during adverse weather; (2) provide guidance through multiple-turn lanes, at merge locations, and As a first step in this synthesis effort, a review of published through tunnels; (3) enhance regulation at intersection stop literature was conducted. A full range of domestic and inter- bars and where left turns are prohibited; and (4) enhance illu- national IPM system applications, including airport and mination at vehicle and truck inspection points and environ- pedestrian crosswalk applications, were considered. Primary mentally sensitive areas. sources of literature included: Although the number and breadth of IPM system applica- Transportation Research Information System (TRIS); tions has increased in recent years, it appears that little is International Transport Research Documentation (ITRD) known about the true effectiveness of these systems in enhanc- database, which includes transportation research of ing roadway safety, operations, or aesthetics. Furthermore, it 23 countries; and is evident that little guidance is available to support proper Conference compendiums such as TRB's annual meet- installation, operation, and maintenance of the systems. ing and ITE district and international meetings. OBJECTIVES Not surprisingly, much of the published literature related to airport and pedestrian crosswalk applications. IPM systems This synthesis report documents the current state of knowledge are more widely implemented and have a longer history of use related to IPM system use and effectiveness. More specifi- in these environments. Limited information was also uncov- cally, the report documents: (1) the state of IPM technology, ered related to the use of IPM systems during adverse weather.