Practices for Preventing Roadway Departures (2018) / Chapter Skim
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Pages 12-42
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From page 12... ...
12 Survey Questionnaire For this synthesis, a questionnaire was sent to DOTs in all 50 states and the District of Columbia. The questionnaire, shown in Appendix A in a condensed form, was organized into five parts.
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Survey of the State of the Practice 13 The responses to these questions are shown in Tables B1 through B4 in Appendix B and are summarized in the following sections. Roadway Departure Safety Implementation Plans (Question 1)
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14 Practices for Preventing Roadway Departures An initial task of analyzing roadway departure crash data is to extract the relevant crashes from the statewide total crash database. This requires defining what constitutes a roadway departure crash and the data elements that capture the relevant crash records.
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Survey of the State of the Practice 15 All 41 states responded that they follow at least two of the approaches, with many following all three; the full results are shown in Table B4 in Appendix B Six states responded that they also use other approaches; three are noted here: • Sites are identified through network screening and further refined through road safety audits (Alabama)
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16 Practices for Preventing Roadway Departures Literature Findings The most recent and comprehensive research on wider edge lines has given evidence of their safety benefits. In their 2013 report, Carlson et al.
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Survey of the State of the Practice 17 particular countermeasure, and the middle three columns show frequency of use. Not all states that responded that they used the countermeasure provided a response as to the frequency of use; hence, for some countermeasures, the sum of the frequency of use and "do not use" will not add to the total number of states responding.)
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18 Practices for Preventing Roadway Departures Literature Findings The literature review did not uncover any studies that reported on the effectiveness of these measures in terms of changes in crashes, nor are they listed in the CMF Clearinghouse. However, Albin et al.
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Survey of the State of the Practice 19 – Concern about vehicles and motorcycles sliding on the markings, particularly if thermoplastic is used. Three states stated that they felt signs could be more effective, and one state commented that it preferred to use other countermeasures such as doubling-up signing, fluorescent sheeting, and sign-mounted flashers.
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Figure 6. Example of a speed warning actuated sign (12)
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Survey of the State of the Practice 21 State Practices Table B9 in Appendix B displays the responses from the 41 states that responded, and Table 6 summarizes these. Twenty-five states indicated that they used this countermeasure, but over half of them stated that it was rare that they did so.
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22 Practices for Preventing Roadway Departures Literature Findings The literature search did not reveal any studies of the safety effectiveness of this countermeasure, but as cited by Albin et al.
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Survey of the State of the Practice 23 (Courtesy of Tracy Lovell, Kentucky Transportation Cabinet)
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24 Practices for Preventing Roadway Departures On rural freeways, edge-line rumble strip studies show that single-vehicle run-off-road fatal and injury crashes can be reduced by nearly 29%. For shoulder rumbles, 14 state and two multistate studies report reductions in single-vehicle run-off-road freeway crashes of 14% to 80%, with most reporting reductions in the 30% to 40% range.
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Survey of the State of the Practice 25 Literature Findings While this device has been used by some states for many years, there had not been any published research evaluating its effect on crashes until an FHWA-sponsored study was completed. The study used data from two-lane and multilane roads in two states -- Florida and South Carolina -- to examine the effects for specific crash types, including total, fatal plus injury, run-off-road, head-on, sideswipe-opposite-direction, sideswipe-same-direction, wet-road, nighttime, and nighttime wet-road crashes.
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26 Practices for Preventing Roadway Departures The SafetyEdge is constructed with a paver attachment that enables the pavement edge to be paved and compacted to a finished 30-degree angle to promote a safe return to the travel lane after a roadway departure. After paving, the SafetyEdge is backfilled and graded flush with the paved surface.
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Survey of the State of the Practice 27 Shoulder Widening on Curved Section (Question 16) Description Shoulders, which can be either paved or non-paved but are usually stabilized, provide an opportunity for an encroaching vehicle to return to the travel lane.
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From page 28... ...
28 Practices for Preventing Roadway Departures Earlier in this chapter, under the section Programmatic Problem Identification and Implementation Strategies, an example was presented of how Arizona applied performance-based practical design as a decision-making approach and evaluation for a shoulder width (and superelevation) improvement project as a countermeasure to a high occurrence of roadway departure crashes.
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Survey of the State of the Practice 29 Literature Findings The safety benefit of this countermeasure has become well established, as reported by Albin et al.
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30 Practices for Preventing Roadway Departures grooves increase pavement macrotexture, thereby increasing or restoring pavement friction. Grooving is typically used on concrete pavements, but it can be used on asphalt pavements (31)
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Survey of the State of the Practice 31 The reasons cited by states that did not use this countermeasure included: • Not aware of the countermeasure (10 states) , • Maintenance concerns (five states)
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32 Practices for Preventing Roadway Departures Some of the comments provided by the states are summarized here: • The results of a study of high-tension cable barriers, completed by Wayne State University (34) , show that cable median barriers have been highly effective at reducing crossover crashes in Michigan.
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From page 33... ...
Survey of the State of the Practice 33 • "The designer may choose to increase the clear-zone width on the outside of horizontal curves where accident histories indicate a need or where specific site investigation shows a definitive accident potential. This may be cost-effective where increased banking or other accident countermeasures are not feasible." • "This is not used that often but is used where there is sufficient ROW [right-of-way]
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34 Practices for Preventing Roadway Departures Some of the comments made were: • "Mostly done during reconstruction. Not an active program to complete this." • "We hope to use this more in the future to help move the cable barrier from the shoulder to the center of the ditch, to help eliminate nuisance hits." • "Typically 3R [resurfacing, restoration, rehabilitation]
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Survey of the State of the Practice 35 From the comments provided by the respondents, it appears that it is difficult to get approval to remove trees and that it is done on a case-by-case basis and not through any general policy or guideline. One respondent commented that they needed better guidance on how this issue relates to speed -- more specifically, at what speed levels does tree removal become more critical.
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36 Practices for Preventing Roadway Departures They also developed CMFunctions that showed that safety benefits may be greater for curves with a larger central angle and where the difference in radius between the before and after period conditions is larger. Their economic analysis revealed a benefit–cost ratio range of 1.75:1 to 4.38:1 (39)
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Survey of the State of the Practice 37 as a roadway departure countermeasure. Based on the comments provided, this improvement appears to be done on a case-by-case basis and frequently is part of a 3R-type project.
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38 Practices for Preventing Roadway Departures • Wider (6-in.) edge line: – Minnesota: 6-in.
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Survey of the State of the Practice 39 11 states that responded that they have used or intend to use the countermeasures are shown in Table B28 in Appendix B Of note are the following: • Georgia conducted research to determine how well pavement joints located at the center of the roadways had been holding up to centerline rumble strips.
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40 Practices for Preventing Roadway Departures comments, which are shown in Table B30 in Appendix B The responses from those states that provided more substantive information are highlighted here: • "We have created a Transportation, Systems, Management and Operations Division to incorporate new technology and develop programs" (Connecticut)
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Survey of the State of the Practice 41 effective at reducing risk of severe crashes, particularly fatal events. We expected high effectiveness (CRF [crash reduction factor]
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From page 42... ...
42 Practices for Preventing Roadway Departures on a new systemic approach that we hope will help us identify high-risk areas and provide justifications." • "Many facets of continuing superelevated shoulders adjacent to the roadway or having a sloped rollover, namely: – Sensitivity of various slope rollovers (2%, 4%, 6%, 8%) , – Effects of slope rollover location with respect to total shoulder width and paved shoulder width, – Effects of slope rollover with respect to interaction with roadside crash barrier, and – Effects of slope rollover with respect to roadway slopes outside of shoulder."
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