U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Agencies that have successfully installed CLRS and SRS on their rural, two-lane and multilane systems generally have formalized processes for systematic installation and for decision-making on corridors that do not meet systematic criteria. It is important to identify corridors that can actually benefit from the treatment and to apply the most effective treatment possible, while considering other roadway users and contexts. This section outlines general model guidance for steps that may be included in a decision-making process, factors to consider, and who may be involved in such a process. Figure 9 provides an overview of the model decision-making framework, which is based on a detailed review of current agency practices across the country. The framework is not intended to be directly applicable to every agency as regulations, policies, practices, and organizational structure can vary across States. The framework offers a structured approach for increasing consistency and the chance of success in installing rumble strips to achieve safety benefits, while providing a context sensitive approach to reduce the impacts on non-motorists.
This model framework is based on an analysis due to systematic installation (e.g., the roadway is being repaved and did not previously have rumble strips). Corridors may also be identified based on crash data analysis and rumble strips may be selected as a candidate treatment. In this case, the installation has already been justified based on crash data and the analyst would begin at Step 3 of the decision-making process presented in Figure 9. There are additional methods for project identification and it is up to the analyst to determine which step to begin with in the process.
This section describes the decision-making process shown in Figure 9. Each decision-point is yes or no after careful consideration by the appropriate parties. Each step includes an overview of the questions or trade-offs that may be considered, the parties involved, and what information is necessary for decision-making. The final decisions include installing standard rumble strips, installing modified rumble strips, installing alternate treatments, or no installation.
Figure 9. Illustration. Model decision-making framework for rumble strip installation.
This step identifies whether or not a corridor is a candidate for installation based on systematic policy. This step typically involves the designer or design team and necessitates information on roadway attributes and operations attributes and generally coincides with resurfacing, rehabilitation, or new construction. If the corridor meets the policy criteria and the policy explicitly considers bicyclists, external noise, and pavement condition, then the standard design can be installed. If the policy does not include these special considerations, then they are addressed in Step 3 (and Step 2 can be skipped). If the corridor does not meet the criteria for systematic installation, then move forward to Step 2.
This step identifies the need for rumble strip installation based on the methods provided in the Rumble Strips and Safety Management section. Although the corridor does not qualify for systematic installation, the corridor may benefit from rumble strip installation. Agencies may consider using a systemic (i.e., risk-based) approach and a high crash corridor approach.
In the systemic approach, analysts identify corridors based on a combination of risk factors, rather than crash history. Crash history can be combined with CMFs for candidate countermeasures in order to determine the potential crash reduction and cost-effectiveness of the proposed measure(s). The systemic approach typically focuses on fatal and severe injury crashes, which are not normally clustered, but provide an opportunity for cost-effective widespread implementation.
In the high crash corridor approach, staff use historical (observed) crashes, expected crashes, predicted crashes, or some combination thereof to identify the need for mitigation. As noted in the High Crash Corridor Safety Approach section, the preferred methods use predicted crashes or expected crashes in the selection of high crash corridors. Once potential mitigation measures are identified, staff apply CMFs in order to determine the potential crash reduction and cost effectiveness of the proposed measures.
In this step, the designer may need to consult with traffic engineers or safety engineers/analysts to develop the justification for installation. If the corridor does not warrant installation, then the decision will be for no installation. If the corridor does warrant installation, then the designer or analyst would document the need and potential safety benefit and move forward to Step 3.
There are three special considerations within this step: pavement condition, bicycle accommodation, and noise accommodation. Each of these are discussed individually.
The pavement should be in good condition (i.e., minimal cracking) and have adequate pavement depth when rumble strips are installed. There is little evidence showing accelerated degradation due to rumble strip installation, but agencies have noted accelerated degradation when the pavement surface was in poor condition. Maintenance personnel may be involved in the decision-making process if the pavement quality is in question, or a pavement quality database can be consulted. If the installation is part of a pavement resurfacing, rehabilitation, or a new construction, then pavement condition is not a concern. Refer to the FHWA Rumble Strip Implementation Guide: Addressing Pavement Issues on Two-Lane Roads for more details on pavement issues.(17) If the pavement condition is adequate or a major reconstruction is more than 3 to 5 years away, then move forward to Step 3b. If the pavement condition does not support installation, then move forward to Step 5.
If bicyclists are not considered in the development of the standard rumble strip design, there are likely to be modifications needed for some installations. Bicyclists have difficulty traversing rumble strips and need adequate clear space on the shoulder and periodic breaks to cross over rumble strips. A non-motorized transportation coordinator (typically the bicycle and pedestrian coordinator) and local stakeholders are consulted to determine if 1) the corridor is a designated bicycle route or 2) if bicyclists utilize the corridor. This consultation utilizes maps of designated bicycle corridors, crowdsourcing technology that identifies bicycle usage, or discussion with those who have local knowledge. Refer to the FHWA Rumble Strip Implementation Guide: Addressing Bicycle Issues on Two-Lane Roads for more details on bicycles issues and accommodation.(13) If it is determined that bicycles use the route, and the standard installation will result in inadequate clear space, then move forward to Step 4. If bicycle accommodation is not a concern, then move forward to Step 3c.
If noise accommodation is not considered in the development of the standard rumble strip design, there are likely to be modifications needed for some installations. Vehicles traversing over rumble strips result in noise that differs from background highway noise, which can disturb nearby residents. An environmental specialist with a background in noise can be consulted to determine if noise is a potential concern for this installation. Refer to the FHWA Rumble Strip Implementation Guide: Addressing Noise Issues on Two-Lane Roads for more details on noise issues and accommodation.(15) The number of receptors, locations of residences, traffic volume, and traffic characteristics are of interest where your agency has no formal policy on noise mitigation. This work utilizes plan-view mapping, site visits, discussion with residents, or discussion with those who have local knowledge. If it is determined that noise accommodation is necessary, then move forward to Step 4. If noise accommodation and bicycle accommodation is not a concern, then the standard rumble strip design may be installed.
Step 4 applies to corridors identified to have bicycle accommodation and/or noise accommodation concerns and roadway elements do not allow for standard installations (e.g., shoulder width too narrow to allow for bicycle clear space). In this step, a rumble strip committee may be consulted to come to a consensus about rumble strip installation and to determine any potential changes to the standard design. The rumble strip committee may include a roadway designer, a non-motorized coordinator, a noise specialist, a traffic or safety engineer/analyst, and an individual from maintenance. At this point, the rumble strip committee can consult with outside stakeholders (e.g., local stakeholders) to weigh the potential safety benefits versus the special considerations. The rumble strip committee will consider the installation of the standard design, potential modifications (e.g., those listed in the Special Considerations section), or not installing rumble strips. Modifications to the design, such as a shallower rumble strip or sinusoidal pattern, may provide adequate warning for motor vehicles and accommodate bicycle and noise concerns. If the committee determines there are too few safety benefits, which do not outweigh other concerns, then move forward to Step 5, otherwise install the recommended design (standard or modified).
If the analyst determines rumble strips are not a viable solution in Step 3a or Step 4, and there is a documented safety problem, then the analyst may consider alternative treatments. The Special Considerations section presents a short list of alternatives for consideration; however, other treatments may not focus on distracted or drowsy driving. The CMF Clearinghouse (www.cmfclearinghouse.org), HSM Part D, the Low-Cost Treatments for Horizontal Curve Safety 2016 guide, and the NCHRP Report 500: Guidance for Implementation of the AASHTO Strategic Highway Safety Plan series may be consulted for additional potential countermeasures. Alternative strategies may be considered based on their effectiveness in reducing the crash type or types of interest. The final decision should be documented along with the expected safety benefit. The rumble strip committee may be involved in the decision-making or the designer can consult with traffic engineering or safety analysts. If no viable alternatives are identified, then the committee or individual may recommend not to install any countermeasures. In this case, the decision should also be documented.
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