Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
43 Findings Primary objectives of this project were to identify countermeasures that state DOTs were using to prevent the occurrence of roadway departure crashes and to mitigate the severity of crashes should they occur. Within those overall objectives, the project was to identify the extent of countermeasure application, the effectiveness of the countermeasures, issues that could hamper their application, and research needed to address any concerns about their use. The information needed to meet these objectives was obtained from a lit- erature search and review as well as a survey of the state DOTsâ practices using an online questionnaire. The survey was distributed to all 50 states and the District of Columbia, with 41 agencies responding. A summary of the key findings from this effort are presented in the following. Roadway Departure Problem Identification and Implementation Programs Roadway departure crashesâdefined by the FHWA as crashes that occur after a vehicle crosses an edge line or centerline or otherwise leaves the traveled wayâaccount for over 50% of all traffic fatalities nationwide. This significant safety issue was recognized in the AASHTO Strategic Highway Safety Plan developed in 1998 and has carried forward in sub- sequent highway safety programs at the federal DOT levelâthrough the FHWAâs Roadway Departure Strategic Approach and Planâand at the state DOT level through state strategic highway safety plans. The survey of the state DOTs revealed that nearly half of the 41 states responding had prepared formal roadway departure implementation plans that recommended installation of low-cost engineering countermeasures. Most states responded that they were using a variety of problem identification and implementation approaches, including: â¢ Traditional hot spot: applying appropriate countermeasures at locations with a high crash frequency or rate, â¢ Systematic: applying specific countermeasures at highway sections that have targeted crash types at or above a crash threshold, and â¢ Systemic: applying countermeasures (typically low cost) at locations based on roadway features correlated with specific severe crash types. C H A P T E R 4 Conclusions
44 Practices for Preventing Roadway Departures Strategies for Preventing Roadway Departure Crashes and Severity The strategic approach to addressing roadway departure crashes is based on objectives or risk categories. The AASHTO Strategic Highway Safety Plan identified these as: 1. Keep vehicles from encroaching on the roadside, 2. Minimize likelihood of crashing into an object or overturning if vehicle travels off the shoul- der, and 3. Reduce the severity of the crash. The FHWAâs strategic approach to effectively prevent roadway departure crashes and fatalities is structured around three objectives: 1. Keep vehicles on roadway, 2. Provide for safe recovery, and 3. Reduce crash severity. These strategies or objectives are similar and are aimed at reducing the occurrence of a roadway departure crash and reducing the severity of a crash should it occur. Within these strategies/ objectives, there are numerous engineering countermeasures. Engineering Countermeasures Used by State DOTs For the purpose of the state survey used for this project, 20 countermeasures were pre- sented, with the intent of determining whether and to what extent the states were using them. Table 22 shows for each of the countermeasures included in the questionnaire the percentage of states that responded with âyesâ (i.e., that they do use the countermeasure) and the percentage that replied with âoften,â âsometimes,â and ârarely.â Unless otherwise indicated, the percentages shown are based on 41 states responding. Observations from this table are: â¢ The countermeasures for which 90% or more of the 41 states replied âyesâ are: â Shoulder rumble strip (100%), â Centerline rumble strip (98%), â Flashing beacon on warning signs (98%), â Tree removal (98%), â Increase sight distance (94%), â Superelevation improvement (93%), â High-friction surface treatment (90%), and â Cable median barrier (90%). â¢ At the other end of the scale, only two countermeasures showed less than 30% of states responding that they were used: â Advance pavement markings for curves (27%), and â Speed advisory marking in lane (22%). The other part of the equation is how frequently the states were using a particular counter- measure. To obtain a measure of this factor, the respondents were given three choices: often, sometimes, and rarely. Without any guidance on what amount of application in terms of miles or number of locations should be assigned to each choice, wide variations among the respon- dents were expected. With that caveat, from the table it can be observed that shoulder rumble strips were being used often by 85% of the states. Other countermeasures being used often, at a level greater than 50%, were SafetyEdge (63%), edge-line rumble strips (59%), cable median barriers (57%), and centerline rumble strips (55%).
Conclusions 45 The survey responses identified the following additional countermeasures: â¢ Passing lanes: Alaska noted that passing lanes on rural two-lane roads (which are com- mon in that state) helped with aggressive driving, which can lead to roadway departure crashes. â¢ Fluorescent yellow sheeting: Used for certain advance curve warning signs. â¢ Culvert extensions: Noted by Hawaii and Alabama, this is a roadside improvement that might prevent rollovers or hitting a fixed object. â¢ LED in-pavement lighting: Noted by two states, this solar-powered delineation device has been used for interchange ramps and curves in rural areas. â¢ Motorcycle barrier attenuator: Noted by Utah, this hardware attaches to standard road- side guardrails to protect errant motorcyclists from impacting the guardrail post during a crash. Safety Benefits of Countermeasures The safety benefit of the identified countermeasures has been researched for the last 30 yearsâ even longer for some. In the last decade or so, more sophisticated and reliable safety analysis tools for beforeâafter evaluations of roadway safety countermeasures, such as the empirical Bayesian approach, have been used to more accurately estimate the change in crashes and severity result- ing from a countermeasure. Crash modification factors and functions have been developed for several of the identified countermeasures; these are found in the CMF Clearinghouse (3). Those Countermeasure Percent of States Responding (%)* Use Counter- measure Frequency of Use Often Sometimes Rarely Traffic control devices Wider edge line 76 39 32 29 Advance curve warning pavement marking 27 18 0 82 Speed advisory marking in lane 22 0 0 100 Speed reduction marking 54 0 0 100 Dynamic curve warning system 61 0 28 72 Flashing beacons on warning sign 98 23 47 30 Shoulder rumble strip** 100 85 8 7 Edge-line rumble stripe 75 59 17 24 Centerline rumble stripe 98 55 32 13 Raised (profiled) pavement markings** 40 44 31 25 Pavement improvements SafetyEdge 85 63 26 11 High-friction surface treatment 90 8 46 46 Pavement grooving*** 49 10 37 53 Roadside measures Cable median barrier 90 57 30 13 Tree removal** 98 10 48 42 Increase clear zone*** 56 9 59 32 Flatten side slope*** 77 10 60 30 Geometric measures Shoulder widening on curved section 73 10 57 33 Increase sight distance on curve** 94 3 58 39 Superelevation improvement** 93 11 43 46 Notes: *Percentage based on 41 states responding unless otherwise indicated. **Percentage based on 40 states responding. ***Percentage based on 39 states responding. Table 22. Frequency of use of countermeasure by states.
46 Practices for Preventing Roadway Departures countermeasures that have been shown to be especially effective in reducing roadway departure crashes or crash severity include: â¢ Shoulder, edge-line, and centerline rumble strips; â¢ SafetyEdge; â¢ High-friction surface treatments; â¢ Cable median barriers; â¢ Increasing clear zones; â¢ Flattening side slopes; and â¢ Increasing sight distances on curves. While these and other countermeasures have shown reductions in crashes or crash severity, there are other factors that influence their cost-effectiveness. States were asked to comment on research they had performed on non-safety impacts, such as durability, life-cycle, and main- tenance needs, which would affect their overall cost-effectiveness. Countermeasures that were being evaluated for these concerns include: â¢ Cable median barriers, â¢ High-friction surface treatments, â¢ Wider edge lines, and â¢ Centerline pavement joints with centerline rumble strips. Concerns Raised by States States were given the opportunity to raise any other issues related to the application of countermeasures for roadway departure crashes. Two issues raised were: â¢ Detrimental driving behaviors such as speeding, driving under the influence of alcohol or drugs, distraction, and fatigue are major contributing factors to roadway departure crashes. Some of the engineering countermeasures, most notably rumble strips, can counteract some of these driver behaviors, but most mentioned in this report will not. Hence, comprehensive safety programs to address roadway departure crashes include enforcement and education strategies. â¢ It is difficult sometimes to convince local road owners (e.g., towns, small counties) to deploy even low-cost sign and marking countermeasures. A systemic approach that identifies high- risk areas is a method for justifying such countermeasures. An overall push to implement as many of the systemic countermeasures as possible as part of a maintenance program may be a cost-effective, long-term solution to bringing down the total number and severity of roadway departure crashes. Influence of Advanced Vehicle Technologies The emergence of autonomous vehicles as well as V2V and V2I technologies may have a pro- found effect on preventing all types of crashes, including roadway departure crashes. However, highway agencies may have to enhance their maintenance activities and modify their traffic control devices to accommodate these smart vehicles. For example, tracking within the travel lanes for autonomous vehicles will require that travel lanes be clearly marked, necessitating a high level of pavement marking maintenance. The development of V2I should bring about more technology for traffic control devices. To examine this issue, two questions were posed to the states concerning what actions, if any, they were pursuing in anticipation of these technologies becoming prevalent on their highway systems. Responses from the states indicated that they had begun to address these issues, albeit in an embryonic stage. For example, Nevadaâs response (âWe are watching this evolution closely and watching for those infrastructure improvements
Conclusions 47 that may be required, such as wider edge lines or Lidar units along the roadwayâ) is reflective of several of the state responses. Conclusions This synthesis project was undertaken to identify and document the practices of the state DOTs in addressing the safety problem of roadway departure crashes through the implementa- tion of engineering countermeasures. From the survey of the states, with 41 responding, and the literature review, the following general conclusions have been drawn: â¢ States recognize the scope and severity of roadway departure crashes and are developing programs for addressing this significant safety problem. Prevention of roadway departure crashes and reduc- tion in their severity is recognized by states in their strategic highway safety plans and, for many states, in the development and implementation of roadway departure safety implementation plans. â¢ States are using alternative approaches for identifying locations for implementation of road- way departure countermeasures, including traditional high-crash (hot-spot), systematic, and systemic approaches. â¢ There are numerous engineering measures (e.g., traffic control devices, geometric design enhancements, pavement treatments, and safety hardware) being used to counter the occur- rence of roadway departure crashes and reduce crash severity. This project identified well over 20 such countermeasures that are being deployed by the states to: â Keep vehicles from encroaching on the roadside or, in the case of two-lane roads, the opposing lane; â Minimize the likelihood of crashing or overturning if a vehicle travels off the shoulder; and â Reduce the severity of crashes. â¢ All of the identified countermeasures have been shown to be effective in reducing the occur- rence of roadway departure crashes or reducing the resulting severity, but to varying degrees and levels of certainty. â¢ Some countermeasures, particularly the use of rumble strips, SafetyEdge, and HFST, have been integrated into state design policies with guidelines established for when they should be used. Suggested Research One of the questions posed to the states asked them to âindicate which of the countermeasures your state is using that need more research.â The collective responses from the states indicated that further research is needed for nearly all of the countermeasures reported on in previous chapters. However, in most responses, the nature or the objective of the research was not specified. Presum- ably, the states wish to be sure that a certain countermeasure would bring about a reduction in roadway departure crashes or a reduction in serious injuries and fatalities. Furthermore, they likely want to know if the countermeasure is cost-effective and will justify the expenditure. These two basic research needs suggest a comprehensive research program that systematically conducts research on the countermeasures. Ideally, for each countermeasure, the following would be addressed: â¢ The safety effect in terms of changes in crashes and severity, with the goal of developing CMFs that could be posted in the CMF Clearinghouse; â¢ The determination of non-safety impacts, such as life-cycle costs, maintenance issues, and public acceptance; and â¢ Guidance for conditions under which the countermeasure is best suited or, on the contrary, should not be used. Much of this information already exists for some of the countermeasures, at least in part. This information needs to be catalogued, documented, and publicized to state and local agencies.