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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2021. Application of Crash Modification Factors for Access Management, Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/26162.
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9 C H A P T E R 2 Literature Review Introduction The objectives of Task 2 were to 1) review the literature related to the safety effects of access management, 2) identify the quality of existing CMFs for access management techniques, and 3) identify access management techniques that are typically applied concurrently and for which cumulative and/or interactive effects must be known. The project team conducted a thorough and critical review of existing published literature from the U.S. and international sources, focusing on definitive access management- related strategies and quantitative, crash-based research. This chapter presents the results of the literature review, structured by strategy. Table 2 provides a list of strategies, sub strategies, and general principles related to access management. Following the table is a description of each strategy with a summary of related CMFs and SPFs, focusing on the availability and quality of quantitative safety information. Table 2. Access management strategies, substrategies, and principles. Strategy Substrategy Applicable Access Management Principles Alternative intersection and interchange design Convert from 4-legged to two 3-legged intersections  Limit the number of conflict points  Separate conflict areas  Manage left-turn movements Install roundabout at roadway intersection Provide median acceleration lane Replace direct left-turn with grade-separated interchange Superstreet (restricted crossing U-turn (RCUT), J-Turn) Convert to jug handle intersections Control driveway design elements Change class/type of driveway  Separate conflict areas  Manage left-turn movements Change movement restriction (e.g., right-in-right- out) Require design of driveways with the appropriate return radii, throat width, channelization, number of lanes and throat length for the type of traffic to be served Convert two-way streets to one-way operation Convert two-way operation to one-way operation  Limit the number of conflict points  Manage left-turn movements

10 Strategy Substrategy Applicable Access Management Principles Establish corner clearance criteria Driveways at signalized intersections  Preserve the functional area of intersections  Separate conflict areas Improve cross- connectivity Allow vehicles to access adjacent properties without returning to the mainline  Limit the number of conflict points  Remove turning vehicles from through-traffic lanes Install two-way left-turn lane (TWLTL) on undivided highway Non-road diet scenarios  Remove turning vehicles from through-traffic lanesRoad diet scenarios Install non-traversable medians, and accommodate left-turns and U-turns Convert traversable median (non-TWLTL) to non-traversable median  Limit the number ofconflict points  Separate conflict areas  Manage left-turn movements Install isolated median barriers Install non-traversable median on undivided highway Replace TWLTL with non-traversable median Install service or frontage roads Change proportion of primary roadway with frontage road  Limit the number of conflict points  Remove turning vehicles from through-traffic lanes Install frontage road to provide access to individual parcels Install traversable medians Convert undivided to divided by traversable median  Separate conflict areas  Manage left-turn movements Left-turn treatment Change storage capacity of existing left-turn deceleration lane  Remove turning vehicles from through-traffic lanes Channelize left-turn lane Control/improve design elements of left-turn lanes Install left-turn deceleration lanes at roadway intersections Provide turning by-pass lanes Prohibit left turn Manage location and spacing of unsignalized access Establish density for unsignalized access (e.g., maximum driveway density)  Limit the number ofconflict points  Separate conflict areas Establish spacing for unsignalized access (e.g., minimum driveway spacing) Establish traffic signal density criteria

11 Strategy Substrategy Applicable Access Management Principles Manage spacing of traffic signals Establish traffic signal spacing criteria  Locate signals to favor through movements  Limit the number of conflict points  Separate conflict areas Manage the location, spacing, and design of median openings and crossovers Create directional median opening  Limit the number of conflict points  Separate conflict areas Install U-turns as an alternative to direct left turns Regulate median opening density Regulate median opening spacing Replace full median opening with median designed for left turns from the major roadway Manage the spacing of signalized and unsignalized access on crossroads in the vicinity of freeway interchanges Establish spacing criteria for interchange ramp terminals  Limit the number of conflict points  Separate conflict areas Provide adequate sight distance at access points Manage design elements to improve sight distance  Preserve the functional area of intersections Manage the location and placement of parking (e.g., replace curb parking with off-street parking or restrict on-street parking near driveways or intersections to improve sight distance) Manage vegetation to improve sight distance (e.g., in landscaped medians or sight triangles) Right-turn treatment Channelize right-turn lane  Remove turning vehicles from through-traffic lanes Control/improve design elements of right-turn lanes Install right-turn deceleration lane at roadway intersections Alternative Intersection and Interchange Design Alternative intersection designs are viewed as access management strategies that may be used to reduce and separate conflict points. While there are a number of at-grade intersection designs that are noticeably different from each other, there is a common aspect among them: the treatment of left-turn movements. As indicated in the FHWA’s Alternative Intersections/Interchanges: Informational Report (AIIR) (Hughes et al. 2010), alternative designs attempt to remove one or more of the conventional left-turn movements from the major intersection. There are safety and operational benefits of these designs, including fewer conflict points and improved signal phasing. An example is a Restricted Crossing U-turn Intersection (RCUT), which is also referred to as a Superstreet or as a J-Turn. As indicated in NCHRP Synthesis 404 (Gluck and Lorenz 2010), superstreets present an alternative left-turn treatment. Instead of allowing left-turn and through movements from side streets to be made directly through a two-way median opening, a superstreet redirects these movements downstream on the major street to a one-way median opening. For example,

12 converting a conventional unsignalized intersection to an unsignalized superstreet is shown to reduce total crashes by 46 percent (Hummer et al. 2010). Installing J-turns is shown to reduce total crashes by 35 percent (Edara et al. 2013). There are additional alternative intersection strategies that include roundabouts and jug handles. The common objective of these strategies is to reduce left-turn conflicts. Roundabouts, for example, involve right-turn movements to enter and exit the intersection. As indicated in the AIIR, although similar in concept to rotaries and traffic circles, roundabouts differ in geometry and operation. The slower speeds and other differences related to roundabouts result in generally safer operations than rotaries and traffic circles. Converting a minor road stop-controlled intersection to a roundabout is shown to reduce total crashes by 70 percent or more (Persaud et al. 2001; Rodegerdts et al. 2007). Converting a signalized intersection to a roundabout is shown to reduce total crashes by up to 67 percent (Rodegerdts et al. 2007; Srinivasan et al., 2011; Uddin et al. 2012). A jug handle intersection is defined by the New Jersey Department of Transportation (NJDOT) Roadway Design Manual (NJDOT 2015) as an at-grade ramp provided at or between intersections to permit motorists to make indirect left turns and/or U-turns. There are several variants of the jug handle, including the forward jug handle, reverse jug handle, and the U-turn ramp jug handle. All of these have the same objective of reducing left-turn movements and the associated conflicts. CMFs for Alternative Intersection and Interchange Design Table 3 provides a summary of CMFs related to the location and spacing of unsignalized access points at the intersection level. Based on a review of the CMF Clearinghouse in June 2017, there were 234 related CMFs, 123 of which were rated 3-star or above. All CMFs available in this category are relevant at the intersection level with no CMFs for the site or corridor level. Table 3. Summary of intersection level CMFs for alternative intersection and interchange design. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Convert from 4-legged to two 3-legged intersections 19 7 4 1 4 2 0 1 Install roundabout at roadway intersection 127 0 5 14 43 59 4 2 Provide median acceleration lane 22 17 5 0 0 0 0 0 Replace direct left-turn with grade-separated interchange 3 0 0 0 3 0 0 0 Superstreet (RCUT, J-Turn) 63 0 27 28 7 1 0 0 Jug handle intersections 0 0 0 0 0 0 0 0 Total 234 24 41 43 57 62 4 3 SPFs for Alternative Intersection and Interchange Design Table 4 provides a summary of SPFs related to alternative intersection designs. These SPFs are relevant at the intersection level with no SPFs for the site or corridor level.

13 Table 4. Summary of SPFs related to alternative intersection designs. Substrategy Intersection-Level SPFs Convert from 4-legged to two 3-legged intersections SPFs for intersections by number of legs and traffic control: SPFs are available for intersections by number of legs and traffic control from many sources, including the Highway Safety Manual (1st Edition). It would be challenging to make credible inferences from the SPFs since factors such as the distance between legs would need to be considered and in general many factors related to differences in location of 3- and 4-leg intersections tend not to be considered in the SPFs. (AASHTO 2010) Install roundabout at roadway intersection SPFs for roundabouts are available in NCHRP Report 572, which are currently being updated in the NCHRP 17-70 project: Comparing these SPF predictions to those available for controlled intersections is unlikely to yield credible CMFs since the two sets of SPFs pertain in general to different jurisdictions and to locations that may have safety related factors that are different for the different site types. (Rodegerdts et al. 2007, Ferguson et al. 2018) The developed SPF was based on a relatively large sample size and included signalized intersections that were not converted to roundabouts and several newly constructed roundabouts in the same jurisdictions that otherwise would have been constructed as signalized intersections. Interaction terms, which were significant for total crashes, allowed investigation of the relationship between traffic volume and the effect of installing roundabouts at signalized intersections. The implied CMF for total crashes indicates that the CMF exceeds 1.0 for annual average daily traffic (AADT) greater than approximately 14,400 vehicles per day. (Gross et al. 2013) Replace direct left- turn with grade- separated interchange SPFs for interchanges are available from NCHRP Project 17-45: These would be applicable not for directly estimating a CMF but for estimating expected changes in safety for a contemplated change from direct left-turn design if the safety of the latter can be reliably estimated from crash history. (Bonneson et al. 2012) Install continuous green T at signalized 3- legged intersection A propensity scores-potential outcomes framework was used to compare the safety performance of the Continuous Green T with conventional signalized T intersections. The results showed that expected total, fatal and injury, and target (rear-end, angle, and sideswipe) crash frequencies were lower at the CGT intersection relative to the conventional signalized T intersection. CMFs of 0.958, 0.846, and 0.920 were estimated for total, fatal and injury, and target (rear-end, angle, and sideswipe) crashes, respectively. (Donnell et al. 2016) Median acceleration lanes, jug handle or superstreet designs. The literature review found no SPFs specifically related to the provision of median acceleration lanes, superstreet, or jug handle designs. Control Driveway Design Elements Driveways are integral to the roadway transportation system. Every driveway connection to a roadway creates an intersection, which in turn creates conflicts for the motorist with bicyclists, pedestrians, and other motor vehicles. Proper driveway design balances the needs of all users by minimizing conflicts while accommodating the demands for mobility and access. As indicated in FHWA’s Access Management in the Vicinity of Intersections (FHWA 2010), driveway connections to public roads must be adequately designed to ensure safe and efficient movement of vehicles to and from the roadway, while balancing safety with mobility interests. There are many elements to consider in proper driveway design, including upstream and downstream sight distance, the angle at which

14 the driveway intersects the major road, the appropriate width of the driveway in tandem with curb radii to accommodate turning movements, the number of lanes (sufficient for the volume at the site), and the vertical grade and length of the driveway throat. In general, driveways should be designed with the appropriate radius, width, and vertical geometry to allow inbound turns to be made without obstructing following through vehicles. In addition, the driveway should be of sufficient length to allow motorists to completely pull off the road without interference from on-site parked vehicles, vehicle queues, or pedestrian or vehicle circulation once they enter the property adjacent to the roadway. The design of a driveway at any given location is a function of the design vehicle, travel speeds to and from the property, traffic volume, pedestrian and bicycle volume, and the type of traffic control. There are limited CMFs to estimate the safety effects of changing these driveway characteristics. For motorists leaving a property, the vertical alignment of the driveway should be as close to level and perpendicular as possible where it intersects with the roadway. The driveway should be level for a sufficient distance to allow the motorist to easily stop with an unobstructed view upstream and downstream prior to entering the major roadway. An FHWA study indicates a potential reduction in crashes at urban, three-legged, stop-controlled intersections with physical turning movement restrictions (compared to similar intersections with no turning restrictions). The CMFs for total, intersection-related, and fatal and injury crashes are 0.55, 0.32, and 0.20 for urban, three-legged, stop-controlled intersections with physical turning movement restrictions compared to similar intersections with no turning restrictions (Le et al. 2018). While there is a potential to reduce crashes at stop-controlled intersections by restricting movements, there is a need to consider the potential for crash migration in determining the net benefits. The same report also indicates a potential increase in total, intersection-related, and fatal and injury crashes at signalized and stop-controlled intersections that are downstream from urban, three-legged, stop-controlled intersections with physical turning movement restrictions (compared to similar intersections with no turning restrictions). The report concludes that this strategy can be cost-effective in reducing crashes, but results may vary by location and there is a need to consider the specific costs and estimated benefits on a case-by-case basis. CMFs for Control Driveway Design Elements Table 5 and Table 6 provide summaries of CMFs related to controlling driveway design elements. Based on a review of the CMF Clearinghouse and related literature, there were 11 related CMFs, all of which were rated 3-star or above (or not yet rated due to recent publication). Among these, 6 CMFs are relevant at the intersection level and 5 CMFs are relevant at the site level. There were no CMFs for the corridor level. Table 5. Summary of intersection level CMFs for control driveway design elements. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Change class/type of driveway 3 0 0 0 3 0 0 0 Change movement restriction (e.g., right-in-right-out) 3 0 0 0 0 0 0 3 Require design of driveways with the appropriate return radii, throat width, channelization, number of lanes and throat length for the type of traffic to be served 0 0 0 0 0 0 0 0 Total 6 0 0 0 3 0 0 0

15 Table 6. Summary of site level CMFs for control driveway design elements. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Change class/type of driveway 2 0 0 0 2 0 0 0 Change movement restriction (e.g., right-in-right-out) 1 0 0 0 1 0 0 0 Require design of driveways with appropriate return radii, throat width, channelization, number of lanes and throat length for the type of traffic to be served 2 0 0 0 2 0 0 0 Total 5 0 0 0 5 0 0 0 SPFs for Control Driveway Design Elements Table 7 provides a summary of SPFs related to driveway design elements. These SPFs are relevant at the site level with no CMFs for the intersection or corridor level. Table 7. Summary of SPFs related to driveway design elements. Substrategy Site-Level SPFs Require design of driveways with the appropriate return radii, throat width, channelization, number of lanes and throat length for the type of traffic to be served SPF exists for access-related crashes including mainline AADT, driveway width, and 95th percentile queue at downstream intersection in peak hour. SPF indicates that wider driveways are associated with more access-related crashes. SPF does not account for driveway volumes or the median design, which are likely related to the driveway width and impact crash risk. (Jafari and Hummer 2013) Changing the movement restriction of driveways or specific driveway design parameters (type of driveway, radii, throat width, channelization, number of lanes, throat length) The literature review found no further SPFs specifically related to changing the movement restriction of driveways or specific driveway design parameters (type of driveway, radii, throat width, channelization, number of lanes, or throat length). Convert Two-Way Streets to One-Way Operation As indicated in FHWA’s Access Management in the Vicinity of Intersections (FHWA 2010), one-way couplets are often found in urban areas and provide access management benefits. One-way streets limit the number of conflicting movements at each intersection. They also limit driveways to right-in-right-out only or left-in-left-out only turning maneuvers. Thus, they reduce the number and types of conflict points that occur at each driveway. One-way streets can also be beneficial for pedestrians crossing the street, requiring them to look for oncoming traffic in one direction only. They also provide additional opportunities to use available roadway width to provide auxiliary lanes for right-turn and/or left-turn movements, reducing conflicts between through and turning vehicles. One-way operation has additional benefits related to traffic signal progression. Converting two-way frontage roads to one-way operation is shown to reduce fatal and injury crashes by up to 68 percent (Eisele et al. 2011). CMFs for Convert Two-Way Streets to One-Way Operation Table 8 provides a summary of CMFs related to two-way to one-way conversion. Based on a review of the CMF Clearinghouse in June 2017, there were 12 related CMFs, 8 of which were rated 3-star or above. All CMFs available in this category are relevant at the site level with no CMFs for the intersection or corridor level.

16 Table 8. Summary of site level CMFs for two-way to one-way conversion. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Convert two-way streets to one-way operation 12 0 0 4 8 0 0 0 Total 12 0 0 4 8 0 0 0 SPFs for Convert Two-Way Streets to One-Way Operation Table 9 provides a summary of SPFs related to one-way roads. There are many sources of SPFs for two- way arterial roads, including the Highway Safety Manual (1st Edition). SPFs available in this category are relevant at the intersection and site level with no SPFs for the corridor level. Table 9. Summary of SPFs related to two-way to one-way conversion. Substrategy Site-Level and Intersection-Level SPFs Convert two-way streets to one- way operation SPFs for one-way arterials will be available when the final report for NCHRP Project 17-58 is released. Comparing these SPF predictions to those available for two-way operation are unlikely to yield credible CMFs since the two sets of SPFs pertain in general to different jurisdictions and to locations that may have safety related factors that are different for the different site types. (Lord et al. 2018) Establish Corner Clearance Criteria Protecting the functional integrity of intersections is extremely important from safety and operations perspectives. One strategy to help accomplish this is to locate driveways outside of the functional area of an intersection. Figure 2 illustrates the physical area of the intersection. Figure 3 illustrates the functional area of the intersection. As shown in Figure 3, the intersection functional area extends beyond the physical intersection limits to include the upstream approaches where deceleration, maneuvering and queuing take place, as well as the downstream departure area beyond the intersection where driveways could introduce conflicts and generate queues backing up through the intersection. As noted in the American Association of State Highway and Transportation Officials’ (AASHTO) A Policy on Geometric Design of Highways and Streets (AASHTO 2011), driveways should not be located within the functional area of an intersection or in the influence area of an adjacent driveway. An FHWA study indicates a potential increase in total crashes for downstream corners with driveways within 50 ft compared to downstream corners with no driveways within 50 ft. The CMFs for total crashes are 1.33 and 1.76 for corner clearance of 50 ft or less on one and two downstream corners, respectively, compared to no driveways within 50 ft of both downstream corners. The report also indicates a potential reduction in total crashes for upstream corners with driveways within 50 ft compared to upstream corners with no driveways within 50 ft (Le et al. 2018). The CMFs for total crashes are 0.82 and 0.67 for corner clearance of 50 ft or less on one and two upstream corners, respectively, compared to no driveways within 50 ft of both upstream corners. The CMFs for limited corner clearance on the downstream corners were consistent with expectation, indicating statistically significant increases in total, fatal and injury, rear-end, sideswipe, right-angle, and nighttime crashes. For limited corner clearance on the upstream corners, the CMFs were counterintuitive, indicating statistically significant decreases in total, fatal and injury, and rear rear-end crashes.

17 Source: Adapted from Transportation Research Circular 456: Driveway and Street Intersection Spacing, Figure 4, p. 16. Reproduced with permission of the Transportation Research Board. Figure 2. Intersection physical area.

18 Source: Adapted from Transportation Research Circular 456: Driveway and Street Intersection Spacing, Figure 4, p. 16. Reproduced with permission of the Transportation Research Board. Figure 3. Intersection functional area. CMFs for Establish Corner Clearance Criteria Table 10 provides a summary of CMFs related to establishing corner clearance criteria. Based on a review of the CMF Clearinghouse in June 2017, there were 19 related CMFs, 15 of which were rated 3-star or above. All CMFs available in this category are relevant at the intersection level with no CMFs for the site or corridor level. Table 10. Summary of intersection level CMFs for establishing corner clearance criteria. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Driveways at signalized intersections 19 0 4 0 15 0 0 0 Total 19 0 4 0 15 0 0 0 SPFs for Establish Corner Clearance Criteria The literature review found no SPFs specifically related to establishing corner clearance criteria.

19 Improve Cross-Connectivity Access management promotes the implementation of shared-access driveways and cross-access easements between (compatible) adjacent properties, where possible, which allow pedestrians and vehicles to circulate between properties without reentering the abutting roadway (see Figure 4). The sharing of access driveways improves roadway safety and operations by reducing the number of conflict points and separating conflict points along these roadways. The longer spacing between access driveways also facilitates the provision of left-turn and right-turn lanes, eliminating conflicts between through and turning movements. In addition, smoother traffic flow on the abutting street helps to reduce the propensity for vehicular crashes and to increase egress capacity. Source: FHWA. Figure 4. Improved access configuration with cross-connectivity. CMFs for Improve Cross-Connectivity The literature review found no CMFs specifically related to cross-connectivity improvements. SPFs for Improve Cross-Connectivity The literature review found no SPFs specifically related to cross-connectivity improvements. Install Non-Traversable Medians, and Accommodate Left-Turns and U- Turns Allowing unrestricted left-turn movements to and from all access driveways increases the number of vehicular conflict points with other vehicles, pedestrians, and bicyclists. Left-turning vehicles have been shown to account for nearly three-quarters (74 percent) of all access-related crashes. Installations of non- traversable (i.e., raised) medians with provisions for median openings to accommodate left-turns and U- turns have proven to be among the most effective techniques for reducing conflicts and improving traffic operations along roadways. Research shows this strategy can reduce total crashes by 14 to 71 percent (Schultz et al. 2008; Yanmaz-Tuzel and Ozbay 2010; Alluri et al. 2012; Abdel-Aty et al. 2014).

20 The installation of a non-traversable median reduces the number of conflicts along a highway corridor by restricting driveways (not located at median openings) to right-in-right-out movements, and directing left-turn and U-turn movements to designated median openings, as shown in Figure 5. Non-traversable medians with designated median openings to allow for left-turn and U-turn movements offer the following advantages over the other types of roadway cross-sections:  Vehicles traveling in opposite directions are physically separated, eliminating the propensity for head- on crashes. Converting a two-way left-turn lane (TWLTL) to a raised median is shown to reduce head- on crashes by up to 73 percent (Abdel-Aty et al. 2014).  When properly designed, the physical space provided for the deceleration and storage of left-turning and U-turning vehicles occurs outside of the through traffic lanes. The resulting reduction in speed differential between the turning and through vehicles improves traffic operations and reduces the potential for crashes.  The number of left-turn conflicts with vehicles, pedestrians, and bicyclists is reduced. Installing a raised median is shown to reduce pedestrians and bicyclists crashes by 29 and 3 percent, respectively (Miranda- Moreno et al. 2011; Alluri et al. 2012).  The non-traversable median provides a refuge area for pedestrians crossing the roadway at intersections. In addition, midblock pedestrian crossings can be provided and signalized without interfering with traffic progression (i.e., by stopping traffic approaching from the left first, and then stopping traffic from the right).  Locations for making left-turns and U-turns are clearly identifiable to the driver, thus reducing driver workload.  Non-traversable medians reduce the frequency and severity of crashes as compared to both undivided roadways and roadways with a TWLTL. Converting a TWLTL to a raised median is shown to reduce total and fatal/injury crashes by up to 47 and 42 percent, respectively (Alluri et al. 2012; Abdel-Aty et al. 2014).

21 Source: Adapted from NCHRP Report 420: Impacts of Access Management Techniques, Figure 30, p. 72. Reproduced with permission of the Transportation Research Board. Figure 5. Allowable traffic movements before and after raised median installation. (Gluck et al. 1999) CMFs for Install Non-Traversable Medians, and Accommodate Left-Turns and U-Turns Table 11 to Table 13 provide summaries of CMFs related to the installation of non-traversable medians at the intersection, site, and corridor level, respectively. Based on a review of the CMF Clearinghouse in June 2017, there were 410 related CMFs, 174 of which were rated 3-star or above.

22 Table 11. Summary of intersection level CMFs for installing non-traversable medians and accommodating left-turns and U-turns. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Convert traversable median (non-TWLTL) to non-traversable median 2 0 0 0 2 0 0 0 Install isolated median barriers 0 0 0 0 0 0 0 0 Install non-traversable median on undivided highway 3 0 0 0 1 0 0 2 Replace TWLTL with non-traversable median 0 0 0 0 0 0 0 0 Total 5 0 0 0 3 0 0 2 Table 12. Summary of site level CMFs for installing non-traversable medians and accommodating left-turns and U-turns. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Convert traversable median (non-TWLTL) to non-traversable median 8 0 0 6 0 2 0 0 Install isolated median barriers 38 0 0 3 3 4 1 27 Install non-traversable median on undivided highway 33 0 4 1 13 1 4 10 Replace TWLTL with non-traversable median 129 0 24 47 58 0 0 0 Total 208 0 28 57 74 7 5 37 Table 13. Summary of corridor level CMFs for installing non-traversable medians and accommodating left-turns and U-turns. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Convert traversable median (non-TWLTL) to non-traversable median 8 0 0 6 0 2 0 0 Install isolated median barriers 29 0 0 3 3 4 1 18 Install non-traversable median on undivided highway 31 0 4 1 12 1 4 9 Replace TWLTL with non-traversable median 129 0 24 47 58 0 0 0 Total 197 0 28 57 73 7 5 27 SPFs for Install Non-Traversable Medians, and Accommodate Left-Turns and U-Turns Table 14 provides a summary of site- and corridor-level SPFs related to non-traversable medians with left- and U-turn provisions. There were no SPFs for the intersection level.

23 Table 14. Summary of SPFs related to installing non-traversable medians and accommodating left- turns and U-turns. Substrategy Site-Level SPFs Corridor-Level SPFs Install non-traversable median on undivided highway Not applicable Corridor level SPFs are available for total, property damage only, and fatal plus injury crashes and addresses presence of TWLTL or non-traversable median. The information is dated, so its relevance may be in question (Brown et al. 1998). NCHRP Report 395 has SPFs for corridor crashes excluding signalized intersections for TWLTL, undivided, and raised curb medians. The information is dated, so its relevance may be in question (Bonneson and McCoy 1997). SPFs are available from which CMFs may be inferred for median opening density (right angle crashes increase for mixed use corridors with increase in density), proportion of segment with TWLTL (rear-end crashes decrease with increase in TWLTL proportion for residential corridors) and proportion with divided median (decrease in right angle crashes for mixed-use corridors with increasing proportion) (Gross et al. 2015). Replace TWLTL with non-traversable median Information is available on distance between driveway exit and downstream U-turn opening. (Liu et al. 2009) Corridor level SPFs are available for total, property damage only, and fatal plus injury crashes and addresses presence of TWLTL or non-traversable median. The information is dated, so its relevance may be in question (Brown et al. 1998). NCHRP Report 395 has SPFs for corridor crashes excluding signalized intersections for TWLTL, undivided, and raised curb medians. The information is dated, so its relevance may be in question (Bonneson and McCoy 1997). SPFs are available from which CMFs may be inferred for median opening density (right angle crashes increase for mixed use corridors with increase in density), proportion of segment with TWLTL (rear-end crashes decrease with increase in TWLTL proportion for residential corridors) and proportion with divided median (decrease in right angle crashes for mixed-use corridors with increasing proportion) (Gross et al. 2015). Persaud et al. inferred CMFs from the Part C Predictive Method for providing a median, depending on AADT and driveway spacing and type. The inferred CMFs show that CMFs are smaller for lower AADT, for higher driveway densities, and for major commercial (compared to major residential) (AASHTO 2010; Persaud et al. 2011).

24 Substrategy Site-Level SPFs Corridor-Level SPFs Provide isolated median barriers or converting non- TWLTL traversable medians to non- traversable medians. The literature review found no SPFs specifically related to isolated median barriers or converting non-TWLTL traversable medians to non- traversable medians. The literature review found no SPFs specifically related to isolated median barriers or converting non-TWLTL traversable medians to non- traversable medians. Install TWLTL on Undivided Highway Like installations of non-traversable medians on formerly undivided highways, installations of TWLTLs offer safety and operational benefits. Compared to undivided highways, TWLTLs allow the deceleration and storage of left-turning vehicles outside of the through traffic lanes. The resulting reduction in speed differential between the turning and through vehicles improves traffic operations and reduces the potential for crashes and crash severity. A cross-section with TWLTL offers the following advantages over an undivided roadway cross-section:  TWLTLs reduce the frequency of crashes as compared to undivided roadways (Gluck et al. 1999),  Vehicles traveling in opposite directions are separated, reducing the potential for head-on crashes, and  The TWLTL provides a refuge area for passenger cars making a two-stage left-turn from a side-street or driveway (i.e., crossing traffic approaching from the left, waiting in the TWLTL, and then merging with traffic approaching from the right). As reported in the Transportation Research Board (TRB) Access Management Manual (2nd Edition), crash models developed for and discussed in NCHRP Report 395, Capacity and Operational Effects of Midblock Left-Turn Lanes, indicated that roadways with a TWLTL and traffic volumes of 17,500 vehicles per day or more are expected to have similar safety performance (e.g., number of crashes per year) as an undivided roadway. It also indicated that TWLTLs do not provide the same safety benefits as non- traversable medians, which help to physically separate opposing traffic (TRB 2014). NCHRP Report 420, after presenting the results of safety analyses comparing non-traversable medians and TWLTLs, indicates that literature compiled since the 1980s reflects the safety benefits of non-traversable medians over TWLTLs (Gluck et al. 1999). Specifically, 4-lane and 6-lane divided roadways with non-traversable medians (and protected left-turn lanes) have shown better safety performance (lower average crash rates) than 5-lane and 7-lane roadways with a TWLTL. A few studies have shown benefits based on before and- after studies of the same roadway; however, most use a cross-sectional comparison of crash rates for the two basic types of roads. While NCHRP Report 420 (page 76) concluded that roadways with non- traversable medians appear safer than similar roadways with TWLTLs, care should be exercised in selecting the appropriate design. Specifically, for roadways with non-traversable medians, there is a need to provide adequate capacity and design at signalized intersections to counteract the potential for crash migration (i.e., the shift in crashes from one location to another) and to mitigate congestion-related collisions. CMFs for Install TWLTL on Undivided Highway Table 15 to Table 17 provide summaries of CMFs related to the installation of TWLTLs on undivided highways at the intersection, site, and corridor level, respectively. Based on a review of the CMF Clearinghouse in June 2017, there were 203 related CMFs, 99 of which were rated 3-star or above.

25 Table 15. Summary of intersection level CMFs for installing TWLTL on undivided highway. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Non-road diet scenarios 3 0 0 0 3 0 0 0 Road diet scenarios 0 0 0 0 0 0 0 0 Total 3 0 0 0 3 0 0 0 Table 16. Summary of site level CMFs for installing TWLTL on undivided highway. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Non-road diet scenarios 68 1 2 7 9 14 5 29 Road diet scenarios 32 0 0 12 16 3 1 0 Total 100 1 2 19 25 17 6 29 Table 17. Summary of corridor level CMFs for installing TWLTL on undivided highway. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Non-road diet scenarios 68 1 2 7 9 14 5 29 Road diet scenarios 32 0 0 12 16 3 1 0 Total 100 1 2 19 25 17 6 29 SPFs for Install TWLTL on Undivided Highway Table 18 provides a summary of SPFs related to TWLTLs. These SPFs are relevant at the corridor level with no SPFs for the intersection or site levels. Table 18. Summary of SPFs related to TWLTLs. Substrategy Corridor-Level SPFs Non-road diet scenarios Corridor SPFs are available for total, property damage only, and fatal plus injury crashes and addresses presence of TWLTL or non-traversable median. The information is dated, so its relevance may be in question (Brown et al. 1998). NCHRP Report 395 has SPFs for corridor crashes excluding signalized intersections for TWLTL, undivided, and raised curb medians. The information is dated, so its relevance may be in question (Bonneson and McCoy 1997). SPFs are available with proportion of TWLTL (rear-end crashes decrease with increase in TWLTL proportion for residential corridors) (Gross et al. 2015). Provides SPFs for 5T (4 lanes plus a TWLTL) and for 4U (4-lane undivided) and 4D (4- lane divided) from which CMFs may be inferred depending on AADT and driveway type and frequency. Indications are that 5T has substantially more crashes, all else being equal, but perhaps all else is not equal in terms of factors not accounted for in the SPFs, including driveway volumes (AASHTO 2010). Road diet scenario The literature review found no SPFs specifically related to providing TWLTL in a road diet scenario.

26 Install Service or Frontage Roads A frontage road is an access roadway that is generally aligned parallel to a main roadway and is located between the right-of-way of the main roadway and the front building setback line. Frontage roads are used as an access management technique to provide direct access to properties and separate through traffic from local access-related traffic. This reduces the frequency and severity of conflicts along the main roadway as well as traffic delays. Installing frontage roads is shown to reduce total crashes by up to 40 percent (Agent et al. 1996). In addition, the resulting increase in spacing between intersections along the main roadway facilitates the design of auxiliary lanes for deceleration and acceleration, further improving traffic safety and operations. A “backage” road—also called a “reverse frontage road” or “reverse access”—serves a similar purpose but is located behind the properties that front the main roadway. Frontage and backage roads may be configured for one-way operation or two-way operation. Figure 6 illustrates one potential frontage road configuration. Source: FHWA. Figure 6. Potential frontage road configuration. CMFs for Install Service or Frontage Roads Table 19 and Table 20 provide summaries of CMFs related to installation of service or frontage roads for the site and corridor level, respectively. Based on a review of the CMF Clearinghouse in June 2017, there were 8 related CMFs, all of which were rated 3-star or above. There were no CMFs for the intersection level as this strategy does not apply to individual intersections. Table 19. Summary of site level CMFs for installation of service or frontage roads. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Change proportion of primary roadway with frontage road 2 0 0 0 2 0 0 0 Install frontage road to provide access to individual parcels 2 0 0 0 0 0 0 2 Total 4 0 0 0 2 0 0 2

27 Table 20. Summary of corridor level CMFs for installation of service or frontage roads. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Change proportion of primary roadway with frontage road 2 0 0 0 2 0 0 0 Install frontage road to provide access to individual parcels 2 0 0 0 0 0 0 2 Total 4 0 0 0 2 0 0 2 SPFs for Install Service or Frontage Roads The literature review found no SPFs specifically related to installation of service or frontage roads. Install Traversable Medians Similar to installations of non-traversable medians and TWLTLs, installations of traversable medians reduce the frequency and severity of crashes as compared to undivided roadways. Installing flush (traversable) medians on undivided roads is shown to reduce total crashes by up to 78 percent (Agent et al. 1996; Gan et al. 2005). While not physically divided, vehicles traveling in opposite directions are further separated, reducing the potential for head-on crashes. The added separation often provides space for left- turn lanes at intersections, allowing the deceleration and storage of left-turning vehicles outside of the through traffic lanes. The resulting reduction in speed differential between the turning and through vehicles improves traffic operations and reduces the potential for crashes. Depending on the type and width of traversable median, it may serve as a refuge area for passenger cars making a two-stage left-turn from a side-street or driveway (i.e., crossing traffic approaching from the left, waiting in the TWLTL, and then merging with traffic approaching from the right). CMFs for Install Traversable Medians Table 21 to Table 23 provide summaries of CMFs related to the installation of traversable medians at the intersection, site, and corridor level, respectively. Based on a review of the CMF Clearinghouse in June 2017, there were 19 related CMFs, 3 of which were rated 3-star or above. Table 21.Summary of intersection level CMFs for installing traversable medians. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Convert undivided to divided by traversable median 0 0 0 0 0 0 0 0 Remove traversable median to convert divided to undivided 1 0 0 0 1 0 0 0 Total 1 0 0 0 1 0 0 0

28 Table 22. Summary of site level CMFs for installing traversable medians. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Convert undivided to divided by traversable median 9 0 0 0 1 0 0 8 Remove traversable median to convert divided to undivided 0 0 0 0 0 0 0 0 Total 9 0 0 0 1 0 0 8 Table 23. Summary of corridor level CMFs for installing traversable medians. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Convert undivided to divided by traversable median 9 0 0 0 1 0 0 8 Remove traversable median to convert divided to undivided 0 0 0 0 0 0 0 0 Total 9 0 0 0 1 0 0 8 SPFs for Install Traversable Medians The literature review found no SPFs specifically related to the installation of traversable medians. Left-Turn Treatment Left-turn movements, especially those that are made from lanes shared with through traffic, cause conflicts and delays. Left-turn lanes provide a refuge for left-turning vehicles by removing those vehicles from the through traffic lane(s). As such, they are an effective means of reducing the conflicts and the speed differential that exists between a turning vehicle and the through vehicles that follow when left turns are made from a shared lane. The addition of exclusive left-turn lanes has been shown to provide a variety of traffic safety and operational benefits, including the following:  Reducing the number of conflicts and crashes (particularly rear-end, angle, and sideswipe crashes),  Physically separating left-turning traffic and queues from through traffic,  Decreasing vehicular delay and increasing intersection capacity,  Providing an area for left-turning vehicles to decelerate outside of the through travel lane, and  Providing greater operational flexibility (e.g., additional traffic signal phasing opportunities). Installing exclusive left-turn lanes is shown to reduce total, fatal/injury, rear-end, and angle crashes by up to 48, 58, 59, and 68, respectively (Harwood et al. 2003; ITE 2004; Srinivasan et al. 2014). In addition, NCHRP Report 745, Left-Turn Accommodations at Unsignalized Intersections (Fitzpatrick et al. 2013) indicated left-turn lanes are likely to be warranted at most unsignalized intersections, (except at those with very low volumes). This is based primarily on the cost savings attributable to an expected decrease in the number of crashes as a result of the left-turn lane installation. CMFs for Left-Turn Treatment Table 24 and Table 25 provide summaries of CMFs related to the left-turn treatment at the intersection and site level, respectively. Based on a review of the CMF Clearinghouse in June 2017, there were 208 related CMFs, 81 of which were rated 3-star or above. There were no CMFs identified for the corridor level.

29 Table 24. Summary of intersection level CMFs for left-turn treatment. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Change storage capacity of existing left-turn deceleration lane 4 0 0 2 2 0 0 0 Channelize left-turn lane 51 0 0 1 6 1 0 43 Control/improve design elements of left-turn lanes 2 0 0 0 2 0 0 0 Install left-turn lanes at roadway intersections 125 0 3 3 16 37 11 49 Provide turning by-pass lanes 12 0 0 1 2 0 0 9 Prohibit left turn 11 0 0 0 0 4 0 7 Total 205 0 3 7 28 42 11 106 Table 25. Summary of site level CMFs for left-turn treatment. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Change storage capacity of existing left-turn deceleration lane 1 0 0 1 0 0 0 0 Channelize left-turn lane 0 0 0 0 0 0 0 0 Control/improve design elements of left-turn lanes 2 0 0 0 2 0 0 0 Install left-turn lanes at roadway intersections 0 0 0 0 0 0 0 0 Provide turning by-pass lanes 0 0 0 0 0 0 0 0 Prohibit left turn 0 0 0 0 0 0 0 0 Total 3 0 0 1 2 0 0 0 SPFs for Left-Turn Treatment The literature review found no SPFs specifically related to intersections with any of the following left- turn treatments:  Length of left-turn deceleration lanes,  Channelized left-turn lanes,  Design elements of left-turn lanes,  Presence of left-turn deceleration lanes,  Provision of turning by-pass lanes, or  Prohibition of left turns. Manage Location and Spacing of Unsignalized Access Access points, commonly referred to as driveways or intersections, introduce conflicts and friction into the flow of traffic along a roadway. Vehicles entering and leaving the roadway often slow the movement of through traffic, and the difference in speeds between through traffic and turning traffic increases the potential for crashes. AASHTO’s A Policy on Geometric Design of Highways and Streets (i.e., the “Green Book”) indicates that the number of crashes is disproportionately higher at driveways than at other intersections. Therefore, driveway design and location merit special consideration (AASHTO 2011).

30 Where an access point is needed, its location should be selected to minimize its adverse effects on roadway safety and traffic flow. Increasing the spacing between access points, through proper planning of future access and closing or consolidating existing access, improves traffic flow and safety along the roadway by:  Reducing the number of conflicts per mile,  Providing a greater distance for motorists to anticipate and recover from turning maneuvers, and  Providing opportunities for the construction of acceleration lanes, deceleration lanes, or exclusive left- turn or right-turn lanes. Reducing driveway density from 48 per mile to 26-48 per mile is shown to reduce injury crashes by up to 29 percent. Reducing driveway density from 26-48 per mile to 10-24 per mile is shown to reduce injury crashes by up to 31 percent. Reducing driveway density from 10-24 per mile to less than 10 per mile is shown to reduce injury crashes by up to 25 percent (Elvik and Vaa 2004). Figure 7 illustrates the spacing distance between two adjacent unsignalized driveways, where the distance is measured from the nearest edges of each driveway. Some agencies choose to measure the spacing distance from the centerlines of the adjacent driveways. Source: FHWA. Figure 7. Illustration of unsignalized driveway spacing. CMFs for Manage Location and Spacing of Unsignalized Access Table 26 to Table 28 provide summaries of CMFs related to managing location and spacing of unsignalized access at the intersection, site, and corridor level, respectively. Based on a review of the CMF Clearinghouse in June 2017, there were 83 related CMFs, 82 of which were rated 3-star or above.

31 Table 26. Summary of intersection level CMFs for managing location and spacing of unsignalized access. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Establish density for unsignalized access (e.g., maximum driveway density) 1 0 0 1 0 0 0 0 Establish spacing for unsignalized access (e.g., minimum driveway spacing) 0 0 0 0 0 0 0 0 Total 1 0 0 1 0 0 0 0 Table 27. Summary of site level CMFs for managing location and spacing of unsignalized access. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Establish density for unsignalized access (e.g., maximum driveway density) 28 0 0 0 24 0 3 0 Establish spacing for unsignalized access (e.g., minimum driveway spacing) 13 0 0 0 13 0 0 0 Total 41 0 0 0 37 0 3 0 Table 28. Summary of corridor level CMFs for managing location and spacing of unsignalized access. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Establish density for unsignalized access (e.g., maximum driveway density) 28 0 0 0 24 0 3 0 Establish spacing for unsignalized access (e.g., minimum driveway spacing) 13 0 0 0 13 0 0 0 Total 41 0 0 0 37 0 3 0 SPFs for Manage Location and Spacing of Unsignalized Access Table 29 provides a summary of corridor-level SPFs related to the location and spacing of unsignalized access points. There were no SPFs identified for the intersection or site level.

32 Table 29. Summary of SPFs related to the location and spacing of unsignalized access points. Substrategy Corridor-Level SPFs Establish density for unsignalized access (e.g., maximum driveway density) NCHRP Report 395 has SPFs for corridor crashes excluding signalized intersections for TWLTL, undivided, and raised curb medians. The information is dated, so its relevance may be in question (Bonneson and McCoy 1997). SPFs are available from which CMFs can be inferred for unsignalized intersection density (e.g., total and turning crashes increase with increased density for mixed use corridors) and access density (crashes increase with increased density) (Gross et al. 2015). Provides corridor SPFs for total, property damage only, and fatal plus injury crashes and addresses access density and proportion of access points that are signalized. The information is dated, so its relevance may be in question (Brown et al. 1998). Persaud et al. inferred CMFs from the Part C Predictive Method. That methodology provides separate models for multi-vehicle driveway and non- driveway crashes per mile, considering the AADT, the number and type of driveways and whether the arterial is divided or undivided. CMFs for reducing driveway density are lower for undivided arterials and for lower AADT (AASHTO 2010; Persaud et al. 2011). Establish minimum spacing of unsignalized access points The literature review found no SPFs specifically related to minimum spacing of unsignalized access points. Manage Spacing of Traffic Signals Establishing traffic signal spacing criteria for arterial roadways is one of the most important and basic access management techniques. These criteria apply to both signalized driveways and signalized roadway intersections. The proper spacing of traffic signals in terms of frequency and uniformity is important because of the effects traffic signals have on arterial safety and traffic flow. Frequency refers to the number of traffic signals for a given length of roadway and is sometimes referred to as “signal density.” It is typically expressed as the number of signals per mile. Uniformity refers to the variation in the distances between individual traffic signals along a given length of roadway. It is desirable to minimize this variation and to space traffic signals at uniform distances, as shown in Figure 8.

33 Source: Adapted from NCHRP Report 420: Impacts of Access Management Techniques, Figure 5, p. 23. Reproduced with permission of the Transportation Research Board. Figure 8. Comparison of uniform and non-uniform signal spacing. (Gluck et al. 1999) Closely-spaced or improperly-spaced traffic signals can result in increased crashes, frequent stops, unnecessary delays for motorists and pedestrians, increased fuel consumption, and excessive vehicular emissions. For example, if a two-mile segment of roadway would require four traffic signals (i.e., a signal density of two signals per mile), it is generally more desirable to space the signals at a uniform distance along the roadway (e.g., every ½ mile), rather than space them irregularly (e.g., 1 mile, ¼ mile, ½ mile, and ¼ mile). Properly-spaced traffic signals allow for the efficient progression of motor vehicle and pedestrian traffic, as well as provide an agency with greater flexibility in developing signal timing plans to reduce traffic conflicts. For example, Figure 9 presents a CMF for estimating the change in total crashes by changing traffic signal density from X to Y signals per mile, where X is the number of signals per mile before and Y is the number of signals per mile after (Schultz et al. 2008). 𝐶𝑀𝐹 𝑒 . Figure 9. Example CMF for total crashes for changing traffic signal density. As another example, Figure 10 presents a CMF for estimating the change in fatal and serious injury pedestrian crashes by changing traffic signal density from X to Y signals per mile, where X is the number of signals per mile before and Y is the number of signals per mile after (Ukkusuri et al. 2011). 𝐶𝑀𝐹 𝑒 . Figure 10. Example CMF for severe crashes for changing traffic signal density.

34 CMFs for Manage Spacing of Traffic Signals Table 30 and Table 31 provide summaries of CMFs related to managing signal spacing at the site and corridor level, respectively. Based on a review of the CMF Clearinghouse in June 2017, there were 20 related CMFs, all of which were rated 3-star or above. This strategy does not apply to the intersection level. Table 30. Summary of site level CMFs for managing spacing of traffic signals. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Establish traffic signal density criteria 3 0 0 0 3 0 0 0 Establish traffic signal spacing criteria 7 0 0 0 7 0 0 0 Total 10 0 0 0 10 0 0 0 Table 31. Summary of corridor level CMFs for managing spacing of traffic signals. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Establish traffic signal density criteria 3 0 0 0 3 0 0 0 Establish traffic signal spacing criteria 7 0 0 0 7 0 0 0 Total 10 0 0 0 10 0 0 0 SPFs for Manage Spacing of Traffic Signals Table 32 provides a summary of corridor-level SPFs related to the spacing of signalized intersections. There were no SPFs identified for the intersection and site level. Table 32. Summary of SPFs related to the spacing of signalized intersections. Substrategy Corridor-Level SPFs Establish traffic signal density criteria SPFs are available from which CMFs for various crash types and severities can be inferred for signalized intersection density (crashes increase with increased density) (Gross et al. 2015). Corridor level SPFs are available for total, property damage only, and fatal plus injury crashes and addresses access density and proportion of access points that are signalized. The information is dated, so its relevance may be in question (Brown et al. 1998). Did not provide a CMF or model for signal spacing directly but found that coordinated intersections are more unsafe than the isolated ones and raised the possibility that the relative short distance between coordinated intersections could lead to more traffic interactions among those intersections, and thus more crashes (Guo et al. 2010). Establish minimum spacing of signalized access points The literature review found no SPFs specifically related to the spacing or minimum spacing of signalized access points.

35 Manage the Location, Spacing, and Design of Median Openings and Crossovers A median opening is an opening in a non-traversable median that provides for crossing and turning traffic. A “full” median opening allows all turning movements, whereas a “partial” median opening allows only specific movements and physically prohibits all other movements. To realize the safety benefits, median openings should not encroach on the functional area of another median opening or intersection. Figure 3 provided an illustration of the functional area of an intersection. For example, Figure 11 presents a CMF for estimating the change in total crashes by changing median opening density from X to Y signals per mile, where X is the number of median openings per mile before and Y is the number of median openings per mile after (Mauga and Kasekoet 2010). 𝐶𝑀𝐹 𝑒 . Figure 11. Example CMF for total crashes for changing median opening density. Converting an open median to a directional median is shown to reduce total crashes and fatal/injury crashes by up to 7 and 23 percent, respectively (Zhou et al. 2013). Converting an open median to a left-in only median is shown to reduce total crashes and fatal/injury crashes by up to 5 and 7 percent, respectively (Zhou et al. 2013). CMFs for Manage the Location, Spacing, and Design of Median Openings and Crossovers Table 33 to Table 35 provide summaries of CMFs related to managing the location, spacing, and design of median openings and crossovers at the intersection, site, and corridor level, respectively. Based on a review of the CMF Clearinghouse in June 2017, there were 94 related CMFs, 72 of which were rated 3-star or above. Table 33. Summary of intersection level CMFs for managing the location, spacing, and design of median openings and crossovers. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Create directional median opening 1 0 0 1 0 0 0 0 Install U-turns as an alternative to direct left turns 18 0 5 0 12 1 0 0 Regulate median opening density 0 0 0 0 0 0 0 0 Regulate median opening spacing 0 0 0 0 0 0 0 0 Replace full median opening with median designed for left turns from the major roadway 1 0 0 0 1 0 0 0 Total 20 0 5 1 13 1 0 0

36 Table 34. Summary of site level CMFs for managing the location, spacing, and design of median openings and crossovers. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Create directional median opening 1 0 0 1 0 0 0 0 Install U-turns as an alternative to direct left turns 18 0 5 0 12 1 0 0 Regulate median opening density 0 0 0 0 0 0 0 0 Regulate median opening spacing 2 0 0 0 2 0 0 0 Replace full median opening with median designed for left turns from the major roadway 15 0 0 2 9 4 0 0 Total 36 0 5 3 23 5 0 0 Table 35. Summary of corridor level CMFs for managing the location, spacing, and design of median openings and crossovers. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Create directional median opening 1 0 0 1 0 0 0 0 Install U-turns as an alternative to direct left turns 18 0 5 0 12 1 0 0 Regulate median opening density 5 0 0 0 5 0 0 0 Regulate median opening spacing 0 0 0 0 0 0 0 0 Replace full median opening with median designed for left turns from the major roadway 14 0 0 2 8 4 0 0 Total 38 0 5 3 25 5 0 0 SPFs for Manage the Location, Spacing, and Design of Median Openings and Crossovers Table 36 provides a summary of corridor-level SPFs related to the location, spacing, and design of median openings and crossovers. There were no SPFs identified for the intersection or site level. Table 36. Summary of SPFs related to the location, spacing, and design of median openings and crossovers. Substrategy Corridor-Level SPFs Regulate median opening density SPFs are available from which CMFs may be inferred for median opening density (right angle crashes increase for mixed use corridors with increase in density) (Gross et al. 2015). Directional median openings, U-turns as an alternative to direct left-turns or median opening spacing or median openings designed for left- turns from the major roadway The literature review found no SPFs specifically related to directional median openings, U-turns as an alternative to direct left-turns, median opening spacing, or median openings designed for left-turns from the major roadway. Manage the Spacing of Signalized and Unsignalized Access on Crossroads in the Vicinity of Freeway Interchanges Freeway interchanges provide the means of moving traffic between freeways and intersecting crossroads. Although direct property access is prohibited on the freeway itself, safety and operational problems can

37 arise when driveways and intersections along the crossroad are spaced too close to the interchange ramp termini. Heavy weaving volumes, complex traffic signal operations, frequent crashes, and recurrent congestion could result. In addition, driveways and median breaks that are provided for direct access to properties along the crossroad compound these problems. Managing access on crossroads in the vicinity of interchanges protects the longevity of both the interchange and the intersecting crossroad by reducing crashes, minimizing congestion, and simplifying driving tasks. Improperly managing access on the crossroad near the interchange may cause congestion and potential crashes, thereby shortening the life cycle of the interchange. In addition, it may cause significant impairment of crossroad and freeway mainline safety and operations. For these reasons, access management should be applied to interchange crossroads such that access points, including both driveways and intersections, are sufficiently separated from freeway interchange ramp termini. While there is limited research in this area, Figure 12 presents three CMFs for estimating the change in total, rear-end, and angle crashes, respectively, by changing the spacing distance between two ramp terminals at a diamond interchange from X to Y feet, where X is the spacing distance before and Y is the spacing distance after (Wang et al. 2011). 𝐶𝑀𝐹 𝑒 . 𝐶𝑀𝐹 𝑒 . 𝐶𝑀𝐹 𝑒 . Figure 12. Example CMFs for ramp terminal spacing. CMFs for Manage the Spacing of Signalized and Unsignalized Access on Crossroads in the Vicinity of Freeway Interchanges Table 37 provides a summary of site-level CMFs related to managing the spacing of signalized and unsignalized access on crossroads in the vicinity of freeway interchanges. Based on a review of the CMF Clearinghouse in June 2017, there were 3 related CMFs, all of which were rated 3-star or above. There were no CMFs identified for the intersection or corridor level. Table 37. Summary of site level CMFs for managing the spacing of signalized and unsignalized access on crossroads in the vicinity of freeway interchanges. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Establish spacing criteria for interchange ramp terminals 3 0 0 0 3 0 0 0 Total 3 0 0 0 3 0 0 0 SPFs for Manage the Spacing of Signalized and Unsignalized Access on Crossroads in the Vicinity of Freeway Interchanges Table 38 provides a summary of intersection-level SPFs related to the spacing of signalized and unsignalized access on crossroads in the vicinity of freeway interchanges. There were no SPFs identified for the site or corridor level.

38 Table 38. Summary of SPFs related to the spacing of signalized and unsignalized access on crossroads in the vicinity of freeway interchanges. Substrategy Intersection-Level SPFs Establish spacing criteria for interchange ramp terminals NCHRP Project 17-45 has SPFs for ramp terminals that consider distance to nearest ramp or intersection. Results show logically that an increase in both fatal plus injury and property damage only crashes is associated with presence and frequency of driveways or unsignalized public street approaches within 250 ft and decreasing distance to the adjacent ramp terminal and intersection (Bonneson et al. 2012). Provides SPFs that relate crashes to access spacing. These were used to develop lookup tables that quantify the impact of access road spacing on the expected number of crashes per unit distance. The tables demonstrate a decrease in the crash rate as the access road spacing increases. The models were said to satisfy statistical requirements (Rakha et al. 2008). Provide Adequate Sight Distance at Access Points The provision of adequate sight distance at all intersections – including driveways – along roadways is a fundamental aspect of traffic operations and safety. Sufficient sight distance is needed to allow drivers to perceive the presence of potentially conflicting vehicles, whether they are relying on a traffic control device to determine right-of-way or, in the absence of such a device, relying on the rules of the road. This perception should occur in sufficient time for drivers to stop or adjust their speed, as appropriate, to avoid a crash. The driver of a vehicle approaching an intersection needs to have not only an unobstructed view of the entire intersection and any traffic control devices, but also sufficient time and distance along the intersecting roadway to anticipate and avoid potential collisions. The sight distance needed under various assumptions of physical conditions and driver behavior is directly related to vehicle speeds and to the resultant distances traversed during perception-reaction time and braking. Specified areas along the intersection’s approach legs and across their corners should be clear of sight obstructions, such as parked vehicles and vegetation, that might block a driver’s view of potentially conflicting vehicles. CMFs for Provide Adequate Sight Distance at Access Points Table 39 provides a summary of intersection-level CMFs related to providing adequate sight distance at access points. Based on a review of the CMF Clearinghouse in June 2017, there were 15 related CMFs, 4 of which were rated 3-star or above. There were no CMFs identified for the site or corridor level.

39 Table 39. Summary of intersection level CMFs for providing adequate sight distance at access points. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Manage design elements to improve sight distance 3 0 0 3 0 0 0 0 Manage the location and placement of parking (e.g., replace curb parking with off-street parking or restrict on-street parking near driveways or intersections to improve sight distance) 3 0 0 0 0 0 0 3 Manage vegetation to improve sight distance (e.g., in landscaped medians or sight triangles) 9 0 2 3 4 0 0 0 Total 15 0 2 6 4 0 0 3 SPFs for Provide Adequate Sight Distance at Access Points The literature review found no SPFs related to providing adequate sight distance at access points. Right-Turn Treatment Right-turn movements, especially those that are made from shared lanes, cause conflicts and delays. Right-turn lanes provide a refuge for right-turning vehicles by removing those vehicles from the through traffic lane(s). As such, they are an effective means of reducing the conflicts and the speed differential that exists between a turning vehicle and the through vehicles that follow when right turns are made from a shared lane. The addition of exclusive right-turn lanes has been shown to provide a variety of traffic safety and operational benefits, including the following:  Reducing the number of conflicts and crashes (particularly rear-end, angle, and sideswipe crashes),  Physically separating right-turning traffic and queues from through traffic,  Decreasing vehicular delay and increasing intersection capacity,  Providing an area for right-turning vehicles to decelerate outside of the through travel lane, and  Providing greater operational flexibility (e.g., additional traffic signal phasing opportunities). Installing exclusive right-turn lanes is shown to reduce total, fatal/injury, rear-end, and angle crashes by up to 26, 23, 65, and 56 percent, respectively (Harwood et al. 2003; Gan et al. 2005). CMFs for Right-Turn Treatment Table 40 and Table 41 provide summaries of CMFs related to right-turn treatments at the intersection and site level, respectively. Based on a review of the CMF Clearinghouse in June 2017, there were 266 related CMFs, 207 of which were rated 3-star or above. There were no CMFs identified for the corridor level.

40 Table 40. Summary of intersection level CMFs for right-turn treatment. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Channelize right-turn lane 4 0 3 0 0 0 0 1 Control/improve design elements of right-turn lanes 20 0 0 16 1 3 0 0 Install right-turn lane at roadway intersections 227 0 0 1 198 3 2 21 Total 251 0 3 17 199 6 2 22 Table 41. Summary of site level CMFs for right-turn treatment. Substrategy Number of CMFs CMF Clearinghouse Star Quality 0 1 2 3 4 5 Not Rated Channelize right-turn lane 0 0 0 0 0 0 0 0 Control/improve design elements of right-turn lanes 16 0 0 16 0 0 0 0 Install right-turn lane at roadway intersections 0 0 0 0 0 0 0 0 Total 16 0 0 16 0 0 0 0 SPFs for Right-Turn Treatment The literature review found no SPFs specifically related to right-turn treatments. Summary The literature review focused on the safety effects of access management strategies, including CMFs and SPFs. The CMF Clearinghouse was the primary source for identifying CMFs, providing more than 1,000 CMFs for the access management strategies of interest. Table 42 provides a summary of all available CMFs and high-quality CMFs (rated 3 stars or higher in the CMF Clearinghouse) for each category and subcategory of access management strategy. The project team also conducted a thorough and critical review of ongoing and completed research to identify potentially relevant SPFs that include access management strategies of interest. Table 43 indicates the availability of relatively high-quality SPFs for each category and subcategory. These summaries provided a basis for the Gap Analysis and helped to inform the prioritization of research conducted in Phase 2.

41 Table 42. Summary of available and high-quality CMFs for each category and subcategory. Strategy Substrategy CMF Available CMF rated 3 stars or higher Alternative intersection and interchange design Convert from 4-legged to two 3-legged intersections 19 6 Install roundabout at roadway intersection 127 106 Provide median acceleration lane 22 0 Replace direct left-turn with grade-separated interchange 3 3 Superstreet (RCUT, J-Turn) 63 8 Convert to jug handle intersections 0 0 Control driveway design elements Change class/type of driveway 5 5 Change movement restriction (e.g., right-in-right- out) 1 1 Require design of driveways with the appropriate return radii, throat width, channelization, number of lanes and throat length for the type of traffic to be served 2 2 Convert two-way streets to one-way operation Convert two-way operation to one-way operation 12 8 Establish corner clearance criteria Driveways at signalized intersections 19 15 Improve cross- connectivity Allow vehicles to access adjacent properties without returning to the mainline 0 0 Install non-traversable medians, and accommodate left-turns and U-turns Convert traversable median (non-TWLTL) to non-traversable median 18 6 Install isolated median barriers 67 17 Install non-traversable median on undivided highway 67 36 Replace TWLTL with non-traversable median 258 116 Install TWLTL on undivided highway Non-road diet scenarios 139 59 Road diet scenarios 64 40 Install service or frontage roads Change proportion of primary roadway with frontage road 4 4 Install frontage road to provide access to individual parcels 4 0 Install traversable medians Convert undivided to divided by traversable median 18 2 Left-turn treatment Change storage capacity of existing left-turn deceleration lane 5 2

42 Strategy Substrategy CMF Available CMF rated 3 stars or higher Channelize left-turn lane 51 7 Control/improve design elements of left-turn lanes 4 4 Install left-turn deceleration lanes at roadway intersections 125 64 Provide turning by-pass lanes 12 2 Prohibit left turn 11 4 Manage location and spacing of unsignalized access Establish density for unsignalized access (e.g., maximum driveway density) 57 48 Establish spacing for unsignalized access (e.g., minimum driveway spacing) 26 26 Manage spacing of traffic signals Establish traffic signal density criteria 6 6 Establish traffic signal spacing criteria 14 14 Manage the location, spacing, and design of median openings and crossovers Create directional median opening 3 0 Install U-turns as an alternative to direct left turns 54 39 Regulate median opening density 5 5 Regulate median opening spacing 2 2 Replace full median opening with median designed for left turns from the major roadway 30 26 Manage the spacing of signalized and unsignalized access on crossroads in the vicinity of freeway interchanges Establish spacing criteria for interchange ramp terminals 3 3 Provide adequate sight distance at access points Manage design elements to improve sight distance 3 0 Manage the location and placement of parking (e.g., replace curb parking with off-street parking or restrict on-street parking near driveways or intersections to improve sight distance) 3 0 Manage vegetation to improve sight distance (e.g., in landscaped medians or sight triangles) 9 4 Right-turn treatment Channelize right-turn lane 4 0 Control/improve design elements of right-turn lanes 36 4 Install right-turn deceleration lane at roadway intersections 227 203

43 Table 43. Summary of available SPFs for each category and subcategory. Strategy Substrategy SPF Available Alternative intersection and interchange design Convert from 4-legged to two 3-legged intersections Yes Install roundabout at roadway intersection Yes Provide median acceleration lane No Replace direct left-turn with grade-separated interchange Yes Superstreet (RCUT, J-Turn) No Convert to jug handle intersections No Control driveway design elements Change class/type of driveway No Change movement restriction (e.g., right-in-right-out) No Require design of driveways with the appropriate return radii, throat width, channelization, number of lanes and throat length for the type of traffic to be served Yes Convert two-way streets to one-way operation Convert two-way operation to one-way operation Yes Establish corner clearance criteria Driveways at signalized intersections No Improve cross- connectivity Allow vehicles to access adjacent properties without returning to the mainline No Install non-traversable medians, and accommodate left-turns and U-turns Convert traversable median (non-TWLTL) to non- traversable median No Install isolated median barriers No Install non-traversable median on undivided highway Yes Replace TWLTL with non-traversable median Yes Install TWLTL on undivided highway Non-road diet scenarios Yes Road diet scenarios No Install service or frontage roads Change proportion of primary roadway with frontage road No Install frontage road to provide access to individual parcels No Install traversable medians Convert undivided to divided by traversable median No Left-turn treatment Change storage capacity of existing left-turn deceleration lane No Channelize left-turn lane No Control/improve design elements of left-turn lanes No Install left-turn deceleration lanes at roadway intersections No Provide turning by-pass lanes No Prohibit left turn No Manage location and spacing of unsignalized access Establish density for unsignalized access (e.g., maximum driveway density) Yes Establish spacing for unsignalized access (e.g., minimum driveway spacing) No

44 Strategy Substrategy SPF Available Manage spacing of traffic signals Establish traffic signal density criteria Yes Establish traffic signal spacing criteria No Manage the location, spacing, and design of median openings and crossovers Create directional median opening No Install U-turns as an alternative to direct left turns No Regulate median opening density Yes Regulate median opening spacing No Replace full median opening with median designed for left turns from the major roadway No Manage the spacing of signalized and unsignalized access on crossroads in the vicinity of freeway interchanges Establish spacing criteria for interchange ramp terminals Yes Provide adequate sight distance at access points Manage design elements to improve sight distance No Manage the location and placement of parking (e.g., replace curb parking with off-street parking or restrict on- street parking near driveways or intersections to improve sight distance) No Manage vegetation to improve sight distance (e.g., in landscaped medians or sight triangles) No Right-turn treatment Channelize right-turn lane No Control/improve design elements of right-turn lanes No Install right-turn deceleration lane at roadway intersections No Chapter 2 References AASHTO. 2010. Highways Safety Manual, 1st edition, Washington, DC. AASHTO. 2011. A Policy on Geometric Design of Highways and Streets. 6th edition, Washington, DC. Abdel-Aty, M., C. Lee, J. Park, J. Wang, M. Abuzwidah, and S. Al-Arifi. 2014. Validation and Application of Highway Safety Manual (Part D) in Florida. Florida Department of Transportation. Tallahassee, Florida. Agent, K., N. Stamatiadis, and S. Jones. 1996. Development of Accident Reduction Factors. KTC-96-13, Kentucky Transportation Cabinet. Alluri, P., A. Gan, K. Haleem, S. Miranda, E. Echezabal, A. Diaz, and S. Ding. 2012. Before-and-after safety study of roadways where new medians have been added. Florida Department of Transportation. Bonneson, A. J., S. Geedipally, M. P. Pratt, D. Lord. 2012. NCHRP 17-45 report: Safety Prediction Methodology and Analysis Tool for Freeways and Interchanges, Transportation Research Board, Washington, DC. Bonneson, J.A., and P.T. McCoy. 1997. NCHRP Report 395: Capacity and Operational Effects of Midblock Left-Turn Lanes, Transportation Research Board, National Research Council, Washington, DC. Brown, H.C., S. Labi, A. P. Tarko, and J.D. Fricker. 1998. A Tool for Evaluating Access Control on High-Speed Urban Arterials – Part 1. Joint Transportation Research Program, Purdue University and Indiana Department of Transportation. Donnell, E, J. Wood, and K. Eccles. 2016. Safety Evaluation of Continuous Green T Intersections. FHWA-HRT-16-036, Federal Highway Administration, Washington DC. Edara, P., C. Sun, and S. Breslow. 2013. Evaluation of J-turn Intersection Design Performance in Missouri. Missouri Department of Transportation. Eisele, W., C. Yager, M. Brewer, W. Frawley, E. Park, D. Lord, J. Robertson, and P. Kuo. 2011. Safety and Economic Impacts of Converting Two-way Frontage Roads to One-way: Methodology and Findings. Report 0-5856-1, Texas Transportation Institute, College Station, TX.

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The 1st Edition, in 2010, of the AASHTO Highway Safety Manual revolutionized the transportation engineering practice by providing crash modification factors and functions, along with methods that use safety performance functions for estimating the number of crashes within a corridor, subsequent to implementing safety countermeasures.

The TRB National Cooperative Highway Research Program's pre-publication draft ofNCHRP Research Report 974: Application of Crash Modification Factors for Access Management, Volume 2: Research Overview documents the research process related to access management features.

Supplementary to the report is the pre-publication draft of NCHRP Research Report 974: Application of Crash Modification Factors for Access Management, Volume 1: Practitioner’s Guide and a summary presentation for the two volumes.

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