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Suggested Citation:"CHAPTER ONE Introduction." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER ONE Introduction." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER ONE Introduction." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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3 significantly greater than those of rural roads. Similarly, Ossenbruggen et al. (2001) studied speeds in rural settle- ments and concluded that a lack of respect for posted speed limits appears to translate into high multivehicle crash rates on posted “low-speed sections” of road. North America’s rural landscape is dotted with isolated villages, settlements, and small towns that are typically located on high-speed rural roads. As traffic enters the set- tlement area a conflict is created, whereby the mobility func- tion of the road is shared with the need to provide access to adjacent lands. A similar concern is present when a highway transitions from a rural to an urban/suburban area. The safety issues respecting rural settlements are at least threefold: • Speed—Motorists traveling at high speeds on the rural roads that lead to rural settlements often do not slow down in the settlement area. • Access Density—The access density (intersections and driveways) in rural settlements is higher than the sur- rounding rural area and increases crash risk. • Road users—Pedestrian and cyclist activity is increased in the rural settlements. Separately and collectively, speed, access density, and vulnerable road users significantly increase crash risk in rural settlements, and are therefore worthy of consideration. This report addresses the speed concern, and in particular engineering and infrastructure solutions to the speed con- cern, at rural-urban transitions. Physical changes to the roadway and its ancillary devices are favored methods of treatment because they typically have permanent and last- ing effects, as opposed to enforcement and education, which are typically transient and less effective. In addition to the speed adaptation phenomenon, inad- vertent speeding in villages may also be exacerbated by the generally abrupt change from the adjoining rural zone to the town or village streetscape. The urban zone is typically dif- ferentiated from the rural zone by changes in land use and in the physical features of the road. Until relatively recently, the transition zone has not usually been thought of as a dis- tinct zone and has not been consciously designed. In most instances, the transition zone is simply a length of rural road- way that is immediately upstream of and adjoining the urban area where the speed transition is expected to occur. CHAPTER ONE INTRODUCTION BACKGROUND Speeding—either exceeding the posted speed limit or travel- ing too fast for ambient conditions—is a major contributing factor to traffic crashes in North America. In 2008, speed- ing was a contributing factor in 31% of all fatal crashes, and 11,674 lives were lost in speeding-related crashes. The National Highway Traffic Safety Administration (NHTSA) estimates that the economic cost to society of speeding- related crashes is $40.4 billion per year (NHTSA 2009). Speeding in urban areas, towns, villages, and other settle- ments is both a safety and a quality of life issue. It is well documented that higher speeds increase the severity of crashes, particularly in crashes with pedestrians and cyclists, and conventional wisdom also suggests that increased speed increases the likelihood of a crash (SWOV 2009). This latter observation is at least in part the result of longer distances traveled during perception-reaction times and the narrowing of the visual field at higher speeds, which makes detection of objects in the periphery more difficult. One of the areas where speeding may be particularly problematic is on the approaches to urban areas from rural areas, where motorists are expected to lower their operating speed from 55 or 60 mph (90 or 100 km/h) to 30 or 40 mph (50 or 65 km/h). These approaches are often called transition zones. A transition zone is a section of road that is continuous with and connects a road section with a high posted speed to a road section with a lower posted speed limit. The transition zones limits are usually defined in the field by either the lim- its of the intermediate speed limit(s), or the location of the reduced-speed-ahead sign (if an intermediate speed limit is not present from the location of the first lower speed limit). The phenomenon known as speed adaptation—the ten- dency for motorists to underestimate their travel speeds after having driven for a long time at a significantly higher speed—may cause motorists to travel faster than they should upon entering the urban area. Researchers have confirmed that during any trip, previous driving at a higher speed for an extended period results in motorists having difficulty in adjusting to a lower speed (Schmidt and Tiffin 1969; Den- ton 1976; and Matthews 1978). In fact, in an examination of transition zones in Australia, Tziotis (1992) found that the injury-producing crash rates on these approaches are

4 ing engineering measures that are used to successfully tran- sition motorists from high-to-low speed areas, identifies unfulfilled needs and knowledge gaps, and identifies design guidance from leading practitioners in the field. The primary audience for this synthesis is DOT personnel involved in speed management, and highway design and traffic opera- tions personnel who have a role in managing speed on the approaches to villages. However, as speed management is a multiple stakeholder activity, policymakers and practitioners from other government agencies and organizations, as well as interest groups and volunteers, may also be interested in this synthesis. STUDY APPROACH The scope of this research was limited specifically to engi- neering measures that are used to transition motorists from high-to-low speed areas. It therefore focused primarily on DOTs and county governments that design and operate high- speed rural road systems. It does not include the broader topic of speed management as it pertains to enforcement, education, and awareness initiatives, or selecting a target speed. Nor does it include techniques and methods used to transition motorists from high-to-low speed conditions in specialized areas such as work zones, toll plazas, and school zones. A 42-question survey was distributed to U.S. and Canadian traffic engineering personnel. The questions were designed to gather information on standard engineering approaches to treating rural high-to-low speed transitions, to obtain infor- mation on enhanced or innovative engineering methods, and to obtain case study information including effectiveness measures. The survey also sought to identify techniques that had been used and found ineffective in transitioning speeds. All the states, the District of Columbia, Puerto Rico, and the 10 provinces and three territories of Canada were invited to participate in the survey. The survey was available as a web survey hosted on the TRB website, as an MS-Word™ tem- plate, and as a paper copy. Each nonresponding jurisdiction was sent a reminder note 2 days before the specified deadline for responses. Subsequent to the deadline for submissions, all nonresponding jurisdictions were contacted by telephone in an effort to obtain a survey response, and deadline exten- sions were permitted to increase the response rate. The sur- vey was also made available to county road agencies through the National Association of County Engineers. A comprehensive literature review of American and inter- national sources was also conducted to assist in establishing practices that have been and are being pursued with respect to speed management at high-to-low speed transitions in rural areas. The literature review encompassed engineer- ing and infrastructure techniques and measures including Speeds on the approaches to villages and urban areas could be better managed if a properly constructed transition zone was introduced. A rural high-to-low speed transition may be defined as a section of road on the approach to a vil- lage, settlement, or urban area from a rural area, over which it is expected that motorists will slow down from the higher speeds associated with rural travel to a speed that is com- mensurate with the urban area. These transitions are also known as urban/rural thresholds. At present, there are no design guidelines for rural speed transitions except for the general guidance provided on reduced-speed-ahead signing in the Manual on Uniform Traffic Control Devices (MUTCD) (FHWA 2003). Figure 1 shows images of the suggested signing. The MUTCD also mentions that a stepped-down speed limit may be more appropriate than a sudden more significant speed reduction. FIGURE 1 Reduced speed ahead signs [Source: FHWA (2003)]. The lack of guidance for practitioners on speed transi- tion zone design is echoed in a recent document that states “[o]ne type of corridor segment that is too often not given the attention it deserves is the ‘transition area’ between the town center and its rural surroundings” (Puget Sound Regional Council 2004). Various road authorities have attempted to manage travel speeds through these settlements by implementing a vari- ety of traffic calming techniques and transitional highway designs. Although states such as Iowa, Minnesota, and Oregon have researched some of their speed transition experiences, the success of the various schemes is largely unpublicized; therefore, the traffic engineering community in North America is still uncertain about the efficacy and applicability of engineering measures to transition speed. The European and United Kingdom (U.K.) experiences are better documented, but are largely unknown to North Amer- ican practitioners. There is clearly a need for more and better information concerning rural high-to-low speed transitions. SYNTHESIS OBJECTIVES This synthesis is a state-of-the-practice report concerning effective and ineffective treatments that state departments of transportation (DOTs) and some overseas agencies have tried for rural high-to-low speed transitions. This report provides information on the state of the practice concern-

5 guidelines and manuals, evaluations of effectiveness, and documented case studies. The practitioner survey and the literature review provide a comprehensive snapshot of the state of the practice con- cerning rural high-to-low speed transitions, and identify both knowledge gaps and trends and patterns concerning successful practices. REPORT ORGANIZATION The first chapter of this synthesis report contains introduc- tory information, including background, objectives, and scope. Chapter two is a literature review, which was con- ducted to identify available techniques, guidelines, and evaluations concerning rural high-to-low speed transition areas. Chapter three documents the survey process and results obtained. Chapter four highlights the existing engi- neering measures for treating high-to-low speed transitions in a toolbox format. Chapter five summarizes the synthe- sis findings and conclusions, including future research that may be considered to understand the extent and usefulness of speed management strategies performed by state DOTs in rural high-to-low speed transition areas.

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TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 412: Speed Reduction Techniques for Rural High-to-Low Speed Transitions explores techniques for lowering traffic speeds in rural transition zones. Transition zones are those portions of high-speed roads that have lower posted speed limits as the roadway approaches a settlement.

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