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SECTION V--DESCRIPTION OF STRATEGIES that strategy will suggest this possibility (in the exhibits, see the attribute area for each strategy entitled "Associated Needs"). Since there are situations where enforcement pro- grams can be designed or enhanced specifically for speeding, there are strategies that discuss this in detail. Strategies to Improve Emergency Medical and Trauma System Services--Treatment of injured parties at highway crashes can have a significant impact on the level of severity, survival rate, and length of time an individual spends in treatment. This is especially true when it comes to timely and appropriate treatment of severely injured persons. Thus, a basic part of a highway safety infrastructure is a comprehensive and well-based emergency care program. While the types of strategies that are included here are often thought of as simply support services, they can be critical to the success of a comprehensive highway safety program. Therefore, for this emphasis area, an effort should be made to determine if there are improvements that can be made in how emergency medical services interact with other safety programs, especially for pro- grams that are focused upon location-specific (e.g., corridors), or area-specific (e.g., rural areas) issues. Strategies Directed at Improving the Safety Management System--There should be a sound organizational structure in place, as well as an infrastructure of laws, policies, etc., to monitor, control, direct, and administer a comprehensive approach to highway safety. It is important that a comprehensive program not be limited to one jurisdiction, such as a state DOT. Local agencies often have jurisdiction over a large portion of the road system and are responsible for its related safety problems. They know, better than others, what the problems are. As additional guides are completed for implementation of the AASHTO Plan, the guides may address the details regarding the design and implementation of strategies for improving safety management systems. Strategies Detailed in Other Emphasis Area Guides--Several of these objectives, and many of the corresponding strategies, are applicable to other emphasis areas. Strategies that overlap between various guides in this NCHRP Report 500 series are discussed briefly in this section, and the other guides (as noted) should be referenced for more details. For example, there are treatments for speeding that would improve safety for all intersection users. Any program targeted at the safety problem covered in this guide on speeding should be created with consideration given to potentially appropriate strate- gies in these other guides. Objective A--Set Appropriate Speed Limits The primary purpose for setting speed limits is to promote highway safety. In addition to safety considerations, decision makers must balance mobility against a need to provide road users with access to adjacent land. Thus, the posted legal limit informs motorists of the maximum driving speeds that decision makers consider reasonable and safe for a road class or highway section under favorable conditions. In addition, speed limits provide the basis for enforcement. Well-conceived speed limits provide law enforcement officers and courts with an indication of appropriate speeds for favorable conditions and thus help target enforcement and sanctions on those who drive at speeds that are excessive for conditions and likely to endanger others (Milliken et al., 1998). V-6

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SECTION V--DESCRIPTION OF STRATEGIES Statutory speed limits, set by federal, state or local government with jurisdiction over roads, are general limits that apply to a given type of roadway. This encourages uniformity in speed limits as well as removes the need to perform engineering studies to determine speed limits for every section of roadway. In many cases, the statutory speed limit is the most appropriate speed limit, but in some situations the statutory limit may not be ideal. In these cases, studies are performed to determine the most appropriate limit for those speed zones. The 85th percentile speed of the current traffic is measured, and the speed limit is initially set at this level. When other factors, such as crash history and traffic and pedestrian volumes, are considered, it may be determined that the 85th percentile speed is not ideal, and the speed limit may be adjusted. A properly set speed limit prompts a reasonable balance between mobility (travel time) and safety (fewer crashes and conflicts) for a certain road class or a specific highway section (Lu et al., 2003). Other factors should be considered when establishing appropriate speed limits. These are particularly important if a full speed study is not being conducted or if the speed limit is being established for a highway on new alignment or a highway under significant reconstruction that is not yet under traffic. What is the type or functional class of the highway (i.e., freeway, arterial, collector, local)? Is the roadway setting urban, suburban, or rural? What is the adjacent land use? What is the type and amount of development? What is the amount of access along the highway? What is the level of access control? Are certain movements restricted by medians or other methods? What is the design speed? What is the highway geometry--horizontally, vertically, and the cross section? What are the speed limits on adjacent roadways? What is the crash history? Have there been speeding-related crashes or crashes involving pedestrians? What is the level of pedestrian usage? Is parking allowed along the street or highway? Are there difficult-to-perceive risks or driving demands or violations of driver expectancy (e.g., isolated curves, heavy vehicle traffic)? All of these issues define the roadway environment and subsequently provide guidance in choosing a speed limit that is reasonable for the typical, prudent driver. Roadways classified as principal or minor arterials are primarily intended to provide for through traffic, in contrast to collector or local streets that mostly serve abutting land uses. The higher type facilities (arterials), which generally carry heavier traffic volume and traverse areas of commercial/industrial land uses, will usually warrant a higher speed limit than collector or local streets. For the latter, the adjacent land uses (i.e., residential, school zone, or playground); access density; and special users (i.e., pedestrians and bicyclists) dictate a slower safe speed. V-7

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SECTION V--DESCRIPTION OF STRATEGIES Setting speed limits too high may be a contributing factor to an increase in the frequency and severity of crashes. Likewise, there are adverse effects when speed limits are set too low. This objective aims to set appropriate speed limits as a proactive approach to preventing the occurrence of speeding-related collisions on new or existing roads. Strategy A1--Set Reasonable and Prudent Speed Limits That Account for Roadway Design, Traffic, and Environment (T) In determining appropriate speed limits for each road type, decision makers should be guided by both the likely risks imposed on others by individual driver speed choices and the availability of information to enable drivers to make appropriate speed choices. They should take enforcement and practicality into consideration. The 85th percentile speed is widely recognized as the most used analytical method for selecting the posted speed limit. The basis of setting the speed limit near the 85th percentile speed is to include as many people traveling at or below the speed limit as is reasonable. Maximizing the number of people traveling at a similar speed helps to minimize speed differentials and conflicts between vehicles. In addition to the 85th percentile speed, decision makers should also request technical information on the following four factors to help guide their determination of appropriate legislated speed limits for a specific road class (Milliken et al., 1998): Design speed, that is the design speed of a major portion of the road, not of its most critical design features (e.g., a sharp curve); Vehicle operating speed, measured as a range of 85th percentile speeds taken from spot-speed surveys of free-flowing vehicles at representative locations along the highway; Safety experience, that is crash frequencies and outcomes; and Enforcement experience, that is, existing speed tolerance (i.e., allowance for driving above the posted speed limit) and level of enforcement. Setting speed limits not only needs to be carefully considered for new roads, but it is also important to periodically review speed limits on existing roads to ensure they are appropriate for the current conditions, especially when there has been a change in the land use, access or traffic characteristics. The Manual on Uniform Traffic Control Devices (MUTCD) offers the following guidance on evaluating speed limits on existing highways (MUTCD, 2003): At least once every 5 years, State and local agencies should reevaluate non-statutory speed limits on segments of their roadway that have undergone significant change in roadway characteristics or surrounding land use since the last review. . . . When a speed limit is to be posted, it should be within 5 mph (10 km/h) of the 85th percentile speed of free-flowing traffic. The process to select the appropriate speed limit should also give consideration to unique or unusual design, traffic, or other environmental issues such as school zones, high percentage of trucks, heavy pedestrian volumes, frequent access or a concentration of elderly pedestrians. For more information, see http:/ /www.mutcd.fhwa.dot.gov. V-8

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SECTION V--DESCRIPTION OF STRATEGIES The speed limit for many new roads may already be defined by a state or local statute (i.e., statutory speed limit for residential areas). However the traffic, design and environmental characteristics of the roadway should still be considered to ensure that the roadway is appropriate for this general speed limit. An engineering study may determine that a speed zone should be established providing a different speed limit for a particular section of a road, or may identify changes in the roadway design to encourage drivers to travel at the appropriate speed. For example, a residential street with a wide cross section and sidewalks with large setback from the travel way may encourage higher speeds than intended by the speed limit, given the desired roadway setting and use. It may be desirable to alter these aspects of the design to encourage lower speeds to better match the context of the facility. See Exhibit V-2 for more information. EXHIBIT V-2 Strategy Attributes for Setting Reasonable and Prudent Speed Limits That Account for Roadway Design, Traffic, and Environment (T) Attribute Description Technical Attributes Target All roads, both existing and planned, are the target for this strategy. The objective in establishing appropriate speed limits is to reduce the number and severity of crashes involving speeding. In addition to setting speed limits appropriately on new roads, speed limits on existing roads should be reviewed, especially if there has been a significant change since the speed limit was last posted. Changes may have been related to traffic (i.e., volumes, vehicle composition, travel speeds, and commuting patterns) or the adjacent land use (including land use type, density, and number of access points). These changes in the roadway environment may not have manifested in a crash experience linked to vehicle speeds yet, but the area may have a high potential for an increase in crash risk due to alterations in traffic and access. Expected Effectiveness It is expected that if drivers perceive a speed limit to be reasonable, they will be more likely to obey it. Many factors--such as traffic volumes, access, and offset to roadside objects--affect driver speed choice, and the speed limit should reflect these factors as well. Research has shown that unreasonably low speed limits significantly increase driver violation of speed limits. Also, lowering or raising speed limits has little effect on a motorist's speed selection. The majority of drivers (about 85 percent) travel at reasonably safe speeds for the various roadway conditions they encounter, regardless of speed limit signs (Parker, 1992). Setting the speed limit at an appropriate level, such as the 85th percentile speed, would then be expected to result in a majority of drivers obeying it. Research has shown that lowering a speed limit will not necessarily encourage people to drive more slowly and obey the new speed limit, at least not without visible enforcement, and that lower speed limits may not necessarily reduce crash rates (Parker, 1992). The effect of the enforcement on speeds does not last long after the enforcement ends. It is believed that the choice of speed limit, and planning and design of the roadway and its environment, should be considered simultaneously in order to best encourage drivers to proceed at the speed intended by the highway agency. V-9

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SECTION V--DESCRIPTION OF STRATEGIES EXHIBIT V-2 (Continued) Strategy Attributes for Setting Reasonable and Prudent Speed Limits That Account for Roadway Design, Traffic, and Environment (T) Attribute Description Keys to Success There are several keys to success associated with this strategy. For existing roadways, it is first appropriate to identify locations where speed limits need to be reevaluated. This may be an extreme horizontal curve or high peak hours of heavy trucks on a certain segment of road. Reviewing crash records for crashes related to speeding or speeds unsafe for conditions is a way to identify locations where speed limits should possibly be evaluated. At these locations, it may also be more appropriate to enhance the roadway or roadside design to better accommodate the speeds allowed by the speed limit. Law enforcement agencies may be another source of information regarding where speed limits need to be reevaluated. Another element of success is involvement of a wide array of agencies when determining appropriate speed limits. Professionals/groups to consider involving when setting speed limits include traffic engineers, law enforcement officials, judges, and public health officials (Milliken et al., 1998). Coordination with enforcement agencies and court systems is especially important if a speed limit will be changed. Clear communication of any changes in the speed limit to the public is important. Enhanced signing may be necessary in areas where the speed limit is changed. If new speed limits are implemented based on design, traffic, and environmental characteristics, some enforcement may be needed. If the speed limit is actually raised, there would be an expectation that fewer drivers would speed, but increased enforcement at these locations would also contribute to decreasing the number of vehicles traveling at excess speeds, at least while the enforcement is in effect. This strategy can be used in conjunction with technology such as variable speed displays or automated speed enforcement devices for better results. It is important that motorists view the speed limit on a specific segment of road to be reasonable and safe. The approach currently used widely in setting speed limits is that maximum speed limits are first legislated broadly by road class and geographic area, and in cases where the statutory limits do not fit specific roadway or traffic conditions, speed zoning practice is applied for that highway section based on engineering study (Lu et al., 2003). Speed limits should be set at levels that are largely self-enforcing or at the lowest speed the law enforcement officials are able to enforce (Milliken et al., 1998). The Federal Highway Administration has developed USLIMITS, a web-based expert systems for use in determining an appropriate speed limit. The tool is based on a similar Australian system, and calculates an appropriate speed limit based on existing operating speeds, crash history, road function, roadside development, pedestrian activity, access frequency, and other factors input by the practitioner. This system can be used by experienced traffic engineers as a source of a second opinion, or as a starting point for smaller agencies with little in-house traffic engineering experience. The output from USLIMITS includes a recommended speed and a list of issues that might be further investigated. USLIMITS is limited to determining appropriate speed limits in speed zones. USLIMITS does not address work zone speed limits, school zone speed limits, or variable speed limits that V-10

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SECTION V--DESCRIPTION OF STRATEGIES EXHIBIT V-2 (Continued) Strategy Attributes for Setting Reasonable and Prudent Speed Limits That Account for Roadway Design, Traffic, and Environment (T) Attribute Description change based on traffic and weather conditions. USLIMITS will be of particular benefit to local communities and agencies that do not have ready access to engineers with speed limit setting expertise. For experienced engineers, USLIMITS can provide an objective second opinion and increase confidence in speed limit setting decisions. Additional information on USLIMITS (and the newly developed USLIMITS2) and a link to the tool can be found online at http://safety.fhwa.dot.gov/ speed_manage/uslimitsbrief.htm. Potential Difficulties One of the main difficulties identified with this strategy involves identifying and properly addressing all issues with setting speed limits. Involving all stakeholders in the process of identifying speed limit-related issues will help obtain all information needed to select the most appropriate speed limit. Another possible difficulty is gaining public acceptance of new speed limits, especially when the reason(s) for a lower speed limit may not be readily apparent. Though local residents and businesses may desire a lower speed limit, it will still likely be difficult to get most drivers to comply with the speed limit without consistent visible enforcement, especially drivers opposed to or unfamiliar with the speed limit changes. Public and political pressure may be applied to a highway agency to change the speed limit on an existing roadway to address a real or perceived safety concern to a limit that may not be optimal for traffic safety and operations. It is important to emphasize that research has shown that changing speed limits has little effect on speeds (Parker, 1992). Appropriate Measures Key process measures include the numbers of existing roadways for which and Data speed limits are reevaluated, and the numbers of new roadways for which speed limits are set considering design, traffic, environmental, and other factors. The number of roadways for which the speed limit is changed based on the reevaluation is another process measure. Measures related to gauging the effectiveness of a legislated speed limit are driver compliance with the speed limit and crash outcomes. Changes in external factors such as new land developments, changes in volume or composition of traffic, and increased (or decreased) cyclist or pedestrian activity also need to be considered in measuring the continued effectiveness of the speed limit. Before and after crash data and average travel speeds can be used to evaluate the effectiveness of changing speed limits. The amount of speed enforcement provided (i.e., patrol hours, vehicles stopped, citations written) before and after a speed limit change should also be recorded to monitor the change and the effort required to enforce such changes. Associated Needs It is important to educate the public--both drivers and residents--that speed limits are set based on the 85th-percentile speed, design factors, traffic conditions, and other related issues for safety purposes. Education and forewarnings may prevent future negative opinions of the speed limit established for a new road or revised speed limits on existing roads. It is very important to inform the public in advance if speed limits will be raised or lowered, as well as when there will be increased enforcement of the new speed V-11

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SECTION V--DESCRIPTION OF STRATEGIES EXHIBIT V-2 (Continued) Strategy Attributes for Setting Reasonable and Prudent Speed Limits That Account for Roadway Design, Traffic, and Environment (T) Attribute Description limits. This can be done during announcements at public meetings or utilizing the local media (television, radio, and newspaper) to notify the public of these changes. An example of materials that instruct the public on how speed limits are set, developed by the Minnesota Department of Transportation, is located online at: http://www.dot.state.mn.us/speed/SpeedFlyer2002.pdf. Coordination with responsible law enforcement agencies is needed to ensure that speed limits are enforced. Organizational and Institutional Attributes Organizational, Institutional Highway agencies should establish procedures for setting speed limits that and Policy Issues include consideration of the factors discussed in this section, and any additional factor that may be an issue in their jurisdiction. Documentation of these decisions should be included in the procedures, as should discussion of involving all interested stakeholders and possible enforcement and education efforts. It is important that law enforcement and traffic court judges perceive that speed limits are reasonable and enforceable (Milliken et al., 1998). Many drivers need to perceive the threat of being cited and of penalties being upheld by courts in order to feel compelled to obey the speed limit. Issues Affecting In most cases, it should take only several months to evaluate and, if necessary, Implementation Time change a speed limit. However, if there is significant disagreement among local residents and businesses regarding a speed limit change, the process might be lengthened significantly. Even so, one could still expect the time to evaluate and select a speed limit to take less than 1 year. Costs Involved Costs associated with this strategy include those related to collecting and analyzing vehicle speeds and crash histories, as well as the acquisition and installation of new speed limit signs. Additional costs might include automated or traditional law enforcement to enforce new speed limits, as well as public information campaigns to inform road users of the new speed limit. Training and Other No extensive training or personnel should be needed for this strategy; however, Personnel Needs someone with experience in selecting speed limits may need to provide assistance in special situations (i.e., school zones, high pedestrian areas, etc.). Legislative Needs None identified. Other Key Attributes Compatibility of This strategy is compatible with all others discussed in this guide. Different Strategies Other Key Attributes to None identified. a Particular Strategy V-12

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SECTION V--DESCRIPTION OF STRATEGIES Strategy A2--Implement Variable Speed Limits (T) Variable speed limits (VSL) are used to encourage drivers to proceed more slowly in certain areas or when driving conditions deteriorate, through the use of changeable message signs or other devices. For example, the speed limit can be lowered during winter driving conditions, when visibility becomes poor due to fog or snow, or when traffic incidents or crashes occur. Events like these that are unpredictable or difficult to predict with precision often require the use of cameras or detection equipment to determine when a speed limit should be changed and to gather data to determine what the speed limit should be. VSL can also be used for more predictable time periods such as in school or construction zones. Near schools speed limits can be lowered during periods of the day when pedestrian activity is high. In many places throughout the United States, flashing lights mounted on a speed limit sign with a legend indicating "School Zone" are used to let the drivers know the change in speed limits near the school while the flashers are operating. Use of VSL, specifically with respect to use in work zones, is discussed in greater detail in Appendix 2 of Volume 17 (Work Zones) of the NCHRP Report 500 series. There is not much existing data to determine the effectiveness of this strategy (Milliken et al., 1998). Due to this uncertainty of effectiveness, in combination with high costs to implement, VSL have not been used widely in the United States for work zones. Their use is often limited to highways and freeways with high volumes of traffic and a frequent occurrence of adverse weather conditions (Milliken et al., 1998). For non-work zone applications, VSL can be determined based on the average speeds on the stretch of roadway over which the limit would apply. Generally all VSL systems will require variable message signs and/or variable speed limit signs, sensors, and some sort of central processing unit to execute control actions. Equipment to detect volumes, speeds, and weather conditions is installed along the roadway, and the collected information is used to automatically determine the speed limit. Several other countries such as the Netherlands, Germany, Sweden, and Australia have also tried VSL (Hines and McDaniel, 2002). VSL in Germany have been more widely accepted by the public than fixed speed limits (FHWA, 1995). Surveys have indicated that German drivers prefer roads with VSL, as it informs them of appropriate travel speeds, and other factors such as congestion, crashes, and lane closures. See Exhibit V-3 for further information. Signs should be posted informing drivers of a reduced speed limit, but periodic enforcement will likely be needed to encourage drivers to slow down as they enter the area. Strategy A3--Implement Differential Speed Limits for Heavy Vehicles if Appropriate (High Speed Only) (T) Some agencies allow posting of a lower speed limit for heavy trucks in an effort to reduce the severity of collisions involving trucks. Differential speed limits are controversial and research is mixed in terms of their effectiveness in reducing crashes. NCHRP Report 500, Volume 13: "A Guide for Reducing Collisions Involving Heavy Trucks," contains a detailed discussion of differential speed limits for heavy vehicles. V-13

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SECTION V--DESCRIPTION OF STRATEGIES EXHIBIT V-3 Strategy Attributes for Implementing Variable Speed Limits (T) Attribute Description Technical Attributes Target Roadways with conditions that may vary are potential locations for variable speed limits (VSL). VSL are most commonly used on highways with one or more of the following characteristics: Traffic congestion Incidents/crashes Inclement weather (snow, ice, fog) Smoke/fog from industrial activity Construction zones School zones Expected Effectiveness Studies on the effectiveness of VSL in the United States have had mixed results regarding impacts on safety (Milliken et al., 1998). Anecdotal information on the effectiveness of reducing speeds or crashes has been mixed, as well (Robinson, 2000). The use of variable speed limits in the Netherlands and Germany (autobahns) found that traffic flow can be improved by reducing travel times by 5 to 15 percent. Accident reductions of 25 to 50 percent have been reported with these systems according to the FHWA Study Tour for Speed Management and Enforcement Technology (FHWA, 1995). Keys to Success Keys to success include developing a procedure for identifying locations that are appropriate for use of VSL, as well as installing detection equipment that can quickly and accurately determine deteriorating driving conditions. Visible enforcement is necessary to encourage compliance with the speed limits. In order for VSL to be enforced, there must be proof of the violators' travel speeds (such as through the use of an enforcement officer patrolling the section of roadway, or through photo radar) and proof that the speeds displayed were visible (since they are often used in adverse conditions such as fog or snow) (Hines and McDaniel, 2002). Enforcing variable speeds can be difficult to implement since there are many different municipal and local jurisdictions that may be involved, which all have separate laws and regulations on the issue (Hines and McDaniel, 2002). The procedure for calculating speed limits should be carefully developed so as to reflect appropriate speeds for current conditions. Procedures developed for using VSL should include direction on how long to keep a reduced speed limit in effect. For weather- or traffic-related reasons for lowering a speed limit, procedures should be established to determine what information from the detectors indicates that it is appropriate to return the speed limit to normal. For scheduled changes in the speed limit, such as for a school zone, the VSL can be preset to begin and end at specific times, or can be controlled with cellular technology or manually on site. In some jurisdictions, school zone speed limits are in effect whenever children are present, and a supplemental plaque to the speed limit sign states this. V-14

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SECTION V--DESCRIPTION OF STRATEGIES EXHIBIT V-3 (Continued) Strategy Attributes for Implementing Variable Speed Limits (T) Attribute Description Potential Difficulties Installation and maintenance of changeable message signs and detection equipment can potentially be difficult, especially if equipment repairs need to be made during inclement weather. The cost of acquiring, installing, and maintaining changeable message signs and detection equipment can be high depending on the complexity of the system. Another potential problem for enforcement is that if a speed limit is changing, law enforcement must be aware of the speed limit currently in effect and also have a way to document this. Appropriate Measures Key process measures include the number of existing roadways for which VSL are and Data considered and implemented. Measures related to gauging the effectiveness of VSL are driver compliance with the speed limit and crash outcomes. Before and after crash data and average travel speeds can be used to evaluate the effectiveness of VSL. The amount of speed enforcement provided (i.e., patrol hours, vehicles stopped, citations written) before and after a speed limit change should also be recorded to monitor the change and the effort required to enforce such changes. Organizational and Institutional Attributes Organizational, Agencies should establish guidelines that specify the conditions under which variable Institutional and Policy speed limits should be considered, and that specify how the speed limits should be Issues established for various conditions. Issues Affecting Implementation costs will vary depending on the complexity of the system. A basic Implementation Time system for a school zone or work zone could be implemented in a relatively short timeframe, but a system involving equipment for detecting changing conditions and changeable message signs, or requiring significant data collection for analysis before designing the system, could take 6 months or more to implement. Costs Involved Also depending on the complexity of the system, this strategy could range from low to high cost. Factors increasing the cost of implementation include data collection and analysis, equipment for detecting incidents, congestion, weather, or other changing conditions, systems for analyzing conditions and determining the appropriate speed, and maintenance of equipment once installed. Training and Other It may be necessary to train key staff and law enforcement staff on how to effectively Personnel Needs use the respective VSL technology, depending on the complexity of the system. Legislative Needs Legislation may be needed to allow agencies to implement variable speed limits, and to establish who has the authority to change speed limits and under what conditions. Other Key Attributes Compatibility of This strategy is compatible with all others discussed in this guide. Different Strategies Other Key Attributes to None identified. a Particular Strategy V-15