Road Safety Audits (RSA)
Road Safety Audit Case Studies: Using Three-Dimensional Design Visualization in the Road Safety Audit Process
Cases in which RSAs May Benefit from 3-D Visualization
Three-dimensional models may require significant time and effort to create and, therefore, may not be cost-effective on all types of projects. Specific characteristics of projects that may benefit from 3-D visualization as a cost-effective tool to improve safety are as follows:
- Large or complex projects
- Innovative or unusual designs
- Significant differences in elevation and/or grade
- Inaccessible locations
- Vital public involvement
Benefits of 3-D Visualization
Generally speaking, the incorporation of 3-D visualization into the RSA process offers a number of tangible benefits:
- The 3-D model enables members of the RSA team who are not proficient at reading and interpreting roadway design plans to grasp the proposed improvements. A typical roadway plan sheet includes a variety of information types, including existing topographic features; existing right-of-way and easements; existing drainage facilities and utilities; property lines; construction baselines; proposed roadway improvements; proposed right-of-way and easements; proposed drainage facilities and utilities; etc. Linework will vary in type, thickness, and color to represent specific components of the roadway environment, and there are various textual and numerical details presented on the sheet. To unfamiliar eyes, a roadway plan sheet may represent little more than "information overload," as the reviewers may not be able to directly decipher the material before them. Because 3-D visualization strives to replicate real-world conditions, it is more easily comprehended by persons of limited roadway design experience.
- The 3-D model can be used to illustrate exactly how the roadway environment will be affected by signs, structures, guardrail, and other key features that are supplemental to the roadway itself. While the characteristics of a roadway's horizontal geometry may be effectively conveyed through a roadway plan sheet, the vertical components of other features may be lost in this traditional 2-D vantage. The 3-D model conveys not only the vertical qualities of the roadway itself-namely its superelevation and the incidence of crest and sag vertical curves-it can also illustrate the 3-D characteristics of other features of the existing or proposed environments. These features may include trees, fence lines, guardrail, and concrete barrier. Furthermore, the accurate incorporation of proposed or existing signs can also be invaluable in allowing the reviewer to observe how the positioning and size of the signs may affect their perceptibility (and, ultimately, their effectiveness) with regard to approaching drivers.
- The 3-D model allows users to view the proposed conditions from any number of vantage points, which may reveal issues not otherwise obvious from a review of standard 2-D plans. A traditional 2-D rendering could be developed to capture the perspective of a driver at a specific location looking at a specific point or in a specific direction, and such a rendering may prove useful to a reviewer. However, if the reviewer then wanted to observe a slightly different vantage (e.g., for a driver positioned 20 ft. to the west or pivoting 15 degrees to the left), then a brand new rendering must be created to accurately recreate that perspective. The development of a series of similar renderings would require significant time and effort. Conversely, the models created here are truly 3-D and allow the user to turn 360 degrees and move about throughout the virtual environment; as such, the models provide the users with essentially every possible vantage that they may desire. This array of available perspectives ranges from an on-the-ground street view to an overhead view and includes every vantage in between. By capturing screen images of various perspectives, users can create a vast collection of viewpoints of the proposed or existing conditions to use for a number of purposes.
- The 3-D model can be used by the RSA team to provide visual support of its findings and recommendations to the project owners, stakeholders, and others. Regardless of whether a recommendation of the team was based on a review of the 3-D model, field observation, or another exercise, 3-D visualization often serves as an effective tool to explain and support that recommendation to the project stakeholders. The unrestricted movement allowed within the parameters of the model affords the team the opportunity to "bring" the stakeholders to the location and vantage in question. One need not rely on the audience members' ability to visualize the roadway environment within their own minds, as that very roadway environment can be explored collectively using 3-D visualization.
- The 3-D model can help to maximize the effective time of the RSA team members. A typical RSA is conducted over two to three consecutive days, with its beginning and ending proceedings-the kickoff and preliminary findings meetings, respectively-scheduled well in advance. These meetings serve as bookends to the multi-day process and establish a finite time frame in which all group activities must transpire. It is, therefore, essential that each group activity is completed in as efficient a manner as possible to maximize the reach of the team in its short time together. By streamlining the process of familiarizing itself with the roadway environment through the review of the 3-D model, the team spends less time comprehending the conditions and more time pondering the potential safety concerns and associated mitigating actions related to those conditions, which, of course, is the overarching goal of any RSA.
- The 3-D model affords the RSA team the opportunity to provide another set of collective eyes in reviewing the project designs and engineering studies. The main purpose of the 3-D visualization is to bring a static design to life for its audience. The RSA team is able to evaluate and validate the appropriateness of many of the design and engineering components because the model brings multiple portions of the design together in an easily comprehensible format. First, it allows the coordinated review of the horizontal and vertical alignments because it presents both simultaneously. Second, because the 3-D model is analyzed in light of other key engineering components beyond the geometric design, it can also bring those pieces to life. For instance, reviewing a traffic impact assessment while simultaneously driving the corridor via the model will assist the RSA team in giving more thoughtful consideration of the projected traffic demands than if that document were viewed independently of the visualization.
There were also several specific benefits realized for the particular projects analyzed here:
- In Rhode Island, the 3-D model helped the team to visualize and understand key engineering concepts. One of the potential benefits of a modern roundabout is a traffic calming effect on vehicular speeds at the intersection. While the departure legs are designed to allow vehicles to exit the circle efficiently, an element of horizontal deflection is incorporated into the design of the approach legs such that drivers are obliged to reduce their speeds in order to navigate the geometry ahead. Excessive speed was a major concern on an urban four-lane arterial considered during the Rhode Island RSA. Posted at 25 mph, this roadway was characterized by exceptionally wide travel lanes (i.e., 15-18 ft) and commonly-observed speeds greater than 40 mph. During the team's comparison between a roundabout and traffic signal along this corridor, 3-D visualization was invaluable in illustrating how the geometric deflection applied to each approach of the roundabout would in essence slow every vehicle that traversed this intersection. The team "drove" in a virtual sense along each approach and observed directly how the horizontal deflection would combine to command deceleration and a heightened awareness of the impending intersection.
- In California, the 3-D model promoted a holistic design approach. Traditionally, the early stages of roadway design focused primarily on establishing "line and grade" (i.e., horizontal and vertical alignments). Oftentimes, little attention was paid to other vital components of the roadway environment (e.g., signs, pavement markings, roadside barriers, etc.) until much later in the design process. At the heart of the California RSA was a complex interchange between an existing Interstate highway and a proposed high-speed multi-lane facility. The 3-D model enabled the RSA team to virtually "drive" along several of the paths within the study area, including the Interstate mainline, several of the interchange ramps, the crossing streets, and a frontage road paralleling the Interstate. Reviewing the model highlighted just how critical the pavement markings and overhead guide signs would be to the safe and efficient operation of the proposed intricate roadway system. As a result, the RSA team recommended that the design team make it a priority to progress the overhead signing plan from a conceptual level to a more advanced state to ensure that critical wayfinding measures can be provided. Additionally, the team discussed the impact of sign structure locations and grading practices on the extent and type of roadside barrier that would be required throughout the project limits. In summary, because it combined all elements of the proposed design, 3-D visualization for California highlighted the importance of a holistic approach to design by simultaneously considering all design features that affect roadway safety-pavement markings, signing (and supporting structures), roadside barriers, etc.
- In Montana, the value of the 3-D model was fully realized when the RSA team considered two separate interchange designs-one of which was modeled while the other was not. Across the four RSAs that comprised this effort, there was a sense that the 3-D visualization offered a real benefit to the RSA team. There was no clearer case presented for this sentiment than the Montana RSA that involved two separate interchange designs. The scope of the visualization effort allowed only one of the alternatives to be modeled; thus, the RSA team had one modeled design and unmodeled design at their disposal. The team was able to conduct a more thorough review and generate a series of detailed recommendations for the interchange design that was modeled. Conversely, for the design alternative not modeled, the team conducted a more basic assessment and was more limited in the overall project visualization and associated depth of potential improvements. The RSA team concluded that the modeling of the second alternative would have enabled it to complete a much more thorough evaluation of the two designs.
- In Rhode Island, the 3-D model allowed for the review of locations that were not readily accessible to the RSA team. A bypass corridor was being considered as a way to alleviate congestion on Aquidneck Island, and the conceptual alignment of this new roadway bisected the secured Naval Station Newport (NAVSTA). Because some sections of the alignment were well within the security fencing at NAVSTA, the RSA team was unable to walk the entire path of the bypass route. However, the 3-D model allowed the team to virtually "drive" the whole corridor and get a general sense of the future roadway environment.
- In Virginia, the 3-D model helped clearly visualize impacts of proposed designs in sensitive areas. The 3-D model was an important element in demonstrating the proposed changes to the public. Since the project passed directly behind houses and a neighboring community, it was important to be able to show the impacts on homeowners and the adjacent community. The extents of the proposed roadway widening and realignment as well as landscaping and fencing placement were all critical to demonstrating the overall project impact. Furthermore, realistically depicting existing features, such as a highly-recognizable convenience store, was key to building confidence in the accuracy of the model. Ultimately, the model was utilized in a public meeting to illustrate the project to all stakeholders.
Visualization Development Efforts
The models developed for these four RSAs were created using Microstation V8 and V8i and then exported to a 3-D PDF format. This technique was used because the 3-D PDF format is easily accessible. The PDF platform is commonly used by many people and can be downloaded for free. During the course of this project the RSA team and roadway owner were able to share and review the 3-D models to ensure their accuracy. In no way is this an endorsement of this or any of the design tools used to create these models. There are many other design visualization design tools and methods that can be used to create a 3-D model. The FHWA Office of Federal Lands Highway Design Visualization Guide provides information on other design visualization techniques and procedures. Detailed information on the techniques used for this project is in Appendix B. A basic review of this process and effort is provided as follows:
- The effort expended in the development of the 3-D models for the four RSAs varied from 100 to 200 person-hours The same individual developed the visualization models for each RSA and estimated his efficiency increased by as much as 40 percent from the first to the last
- Trimble 3-D warehouse was used to secure some of the supplemental elements, such as light poles
- Information requested from the project design team included a variety of files:
- Proposed CAD linework (both 2-D and 3-D, if available) for all improvements, including pavement markings.
- Existing and proposed digital terrain models (DTMs) or triangulated irregular networks (TINs).
- Supplemental files, such as pavement marking plans and typical sections for bridge designs.
- PDF of the entire plan set.
- For the RSA conducted in Rhode Island, DTMs were not provided Rough elevation information was pulled from an on-line mapping resource, which increased the overall level of effort needed to create the 3-D model
- For the RSA conducted in Montana the proposed on ramp design was not provided in CAD and therefore had to be created in the 3-D model, thereby increasing the overall level of effort needed
