Application of Crash Modification Factors for Access Management, Volume 2: Research Overview (2021) / Chapter Skim
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Pages 10-39
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10 Literature Review Introduction The objectives of Task 2 were to (1) review the literature related to the safety effects of access management, (2)
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Literature Review 11 (continued on next page) Table 2.
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12 Application of Crash Modification Factors for Access Management or more (Persaud et al. 2001; Rodegerdts et al.
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Literature Review 13 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 (FHWA n.d.)
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14 Application of Crash Modification Factors for Access Management property, traffic volume, pedestrian and bicycle volume, and the type of traffic control. CMFs to estimate the safety effects of changing these driveway characteristics are limited.
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Literature Review 15 The report concludes that this strategy can be costeffective in reducing crashes, but results may vary by location and there is a need to consider the specific costs and estimated benefits on a casebycase basis. CMFs for Controlling Driveway Design Elements Tables 5 and 6 provide summaries of CMFs related to controlling driveway design elements.
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16 Application of Crash Modification Factors for Access Management opportunities to use available roadway width to provide auxiliary lanes for rightturn and/or leftturn movements, reducing conflicts between through and turning vehicles. Oneway oper ation has additional benefits related to traffic signal progression.
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Literature Review 17 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.
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18 Application of Crash Modi cation Factors for Access Management SPFs for Establishing Corner Clearance Criteria e literature review found no SPFs speci cally related to establishing corner clearance criteria. Improve Cross Connectivity Access management promotes the implementation of shared-access driveways and cross-access easements between (compatible)
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Literature Review 19 SPFs for Improving Cross Connectivity The literature review found no SPFs specifically related to crossconnectivity improvements. Install Non-Traversable Medians and Accommodate Left Turns and U-Turns Allowing unrestricted leftturn movements to and from all access driveways increases the number of vehicular conflict points with other vehicles, pedestrians, and bicyclists.
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20 Application of Crash Modi cation Factors for Access Management • e number of le -turn con icts with vehicles, pedestrians, and bicyclists is reduced. Installing a raised median is shown to reduce pedestrian and bicyclist crashes by 29 and 3 percent, respectively (Miranda-Moreno et al.
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Literature Review 21 Install a Two-Way Left-Turn Lane on an Undivided Highway Like installations of nontraversable medians on formerly undivided highways, installations of TWLTLs offer safety and operational benefits. Compared to undivided highways, TWLTLs allow the deceleration and storage of leftturning vehicles outside of the throughtraffic lanes.
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22 Application of Crash Modification Factors for Access Management Table 14. Summary of SPFs related to installing non-traversable medians and accommodating left turns and U-turns.
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Literature Review 23 As reported in the second edition of the Access Management Manual (Williams et al.
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24 Application of Crash Modification Factors for Access Management 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 rightofway 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 accessrelated traffic.
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Literature Review 25 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 ush (traversable)
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26 Application of Crash Modification Factors for Access Management CMFs for Installing Traversable Medians Tables 21 to 23 provide summaries of CMFs related to the installation of traversable medians at the intersection, site, and corridor levels, respectively. Based on a review of the CMF Clearinghouse in June 2017, there were 19 related CMFs, three of which were rated three stars or higher.
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Literature Review 27 • Providing an area for leftturning vehicles to decelerate outside of the through travel lane, and • Providing greater operational flexibility (e.g., additional traffic signal phasing opportunities)
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28 Application of Crash Modification Factors for Access Management 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 speed between through traffic and turning traffic increases the potential for crashes.
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Literature Review 29 of the CMF Clearinghouse in June 2017, there were 83 related CMFs, 82 of which were rated three stars or higher. SPFs for Managing Location and Spacing of Unsignalized Access Table 29 provides a summary of corridorlevel SPFs related to the location and spacing of unsignalized access points.
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30 Application of Crash Modification Factors for Access Management four traffic signals (i.e., a signal density of two signals per mile) , it is generally more desir able to space the signals at a uniform distance along the roadway (e.g., every ½ mile)
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Literature Review 31 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.
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32 Application of Crash Modification Factors for Access Management Figure 11. Example CMF for total crashes for changing median opening density.
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Literature Review 33 Substrategy Numberof 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 34. Summary of site-level CMFs for managing the location, spacing, and design of median openings and crossovers.
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34 Application of Crash Modification Factors for Access Management 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.
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Literature Review 35 they are relying on a traffic control device to determine rightofway 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.
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36 Application of Crash Modification Factors for Access Management SPFs for Providing Adequate Sight Distance at Access Points The literature review found no SPFs related to providing adequate sight distance at access points. Right-Turn Treatment Rightturn movements, especially those that are made from shared lanes, cause conflicts and delays.
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Literature Review 37 Strategy Substrategy CMF Available CMF rated 3 stars or higher Alternative intersection and interchange design Convert from 4-legged intersection to two 3legged intersections 19 6 Install roundabout at roadway intersection 127 106 Provide median acceleration lane 22 0 Install continuous green T at signalized 3-legged intersection 3 3 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-rightout)
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38 Application of Crash Modification Factors for Access Management Strategy Substrategy CMF Available CMF rated 3 stars or higher 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)
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Literature Review 39 Strategy Substrategy SPF Available 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 onstreet parking near driveways or intersections to improve sight distance) No Manage vegetation to improve sight distance (e.g., in landscaped medians or sight triangles)
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