U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
REPORT |
This report is an archived publication and may contain dated technical, contact, and link information |
|
Publication Number: FHWA-HRT-17-048 Date: May 2018 |
Publication Number: FHWA-HRT-17-048 Date: May 2018 |
Following on the initial screening of previous related work, the literature review, and an initial examination of attributes related to interchange complexity, the project team selected four States to serve as partners in this project. The intention of the State transportation department participation was to permit for streamlined access to sites for data collection purposes and the easy acquisition of background information on safety performance and traffic operations related to each site selected from those under the jurisdiction of the participating agencies. This process included the selection of partnership States, the preliminary site list, and the final site list. The site selection process was detailed in the Site Selection Report[1], submitted in December 2014, and that information is included here.
The process of selecting participating States was conducted in coordination with FHWA and the technical evaluation panel. The project team identified seven characteristics of a suitable partnership agency:
Subsequent to a review of the States meeting these characteristics, the project team identified four suitable agencies. These agencies and the characteristics of the complex interchanges within their jurisdictions are listed in table 36.
TH 62 = State Trunk Highway 62.
Each State was invited to sign a partnership agreement. The intent of the agreements was to clearly define relationships and responsibilities for the involved parties, identify areas where State transportation department contributions could occur, manage the relationships and contacts with agency staff, and provide a managed scope for efforts in support of the research project.
All four agencies provided prompt communication. The sheer size of agency operations, however, precluded timely information on sign replacement projects throughout each jurisdiction, and individual project delays that were beyond the control of the project team prevented some data collection activities from taking place during the course of the project.
Some State agencies have produced comprehensive materials in support of freeway design tasks (e.g., interchange configuration, ramp terminal design, freeway corridor design, and the design of freeway signing and pavement markings).
MnDOT produces a document that addresses specific sign-design criteria, using FHWA publications as a basis for design assistance. The MnDOT Traffic Guide Sign Design Manual provides design criteria not specifically addressed in the MUTCD or the Standard Highway Signs Catalog (SHS).(34,35) For example, the manual provides specific information on fractions sizes and the design and use of guide sign arrows. Publications from other agencies address other aspects of guide sign design, including the arrangement of the legend, a method for determining how many legend elements appear on a sign (for sizing of signs where standard legend sizes are not used), and specific design and use criteria for signs related to tolling systems.
In tasks 4 and 5, the project team conducted testing and evaluation of various traffic engineering treatments in an effort to demonstrate which treatments are likely to address specific HFs, operational, and safety performance needs in the complex interchange environment. Field work at these interchanges was the basis for evaluations of real-world driver behavior. While the team anticipated data collection concomitant with regular signing replacement and upgrading work, internal agency communications and the proximity of other construction contracts prevented this from being a practical work product during this project.
The original candidate site list numbered 70 interchanges from throughout the United States and Canada. The initial 35 junctions were compiled during the development of the complex interchanges spreadsheet tool. The remaining 35 interchanges were selected by the project team. Factors influencing the selection included the following:
The project team did not analyze crash history in the selection process. However, in some cases, selected interchanges were inclusive of geometric design features that appear to have been subject to various safety treatments in an effort to mitigate crashes. The team’s field visits to these sites included an examination of roadside design elements and the presence of devices used to reduce the severity of roadway departure crashes, including redirective elements and energy dissipating elements. In some cases, obvious or known retrofits of upgraded impact attenuation equipment indicated that task saturation or insufficient information may be occurring upstream of that location.
In the original process, the project team considered interchanges located in Canada. Signing and pavement markings in Canada differ, in some cases, from applications in the United States. One interchange in British Columbia was newly constructed and features an application of blended APL signing that is similar to the practice outlined in the 2009 MUTCD. The team chose not to conduct field analysis at these sites, owing to the complexity of international travel and the provision of suitable sites within the United States.
Table 37 lists the interchanges that were selected as candidate sites for further evaluation, including the gathering of data, photographs, and other information.
Not all of the candidate interchange sites were included in evaluation and study activities. Additional sites were selected for the final list so that some redundancy in site availability would be possible in case of unplanned impacts to sites. For this project, sites 25, 26, 27, 28, 32, 33, 41, and 42 were not evaluated using field data collection. For these sites, evaluation was limited to the collection of photographs and observations based on drive-through activities. Complete descriptions of the field study sites are provided in chapter 7.
In addition, the initial candidate list included three sites from California. Because California was not selected to be a participating State, these locations were not included for evaluation with field study activities. The sites did provide important context, however, for how agencies deal with multiple exiting lanes, direct-access ramps from restricted lanes, and C/D roadway systems. Each of these sites, listed in table 38, exhibits attributes related to complexity.
For each interchange, a separate sheet has been provided. These interchange description sheets include satellite imagery of the interchange and a brief description of specific characteristics that set that particular interchange apart from others. This information is included in appendix A.
The sites selected for evaluation are inclusive of interchanges and freeway corridor segments. Within each site, several locations may be identified to help adequately describe the specific areas of individual study tasks. For example, site 31 has been divided into three locations, location 31-1, location 31-2, and location 31-3, each inclusive of one approach to the interchange.
The site selection process and the work of the practices evaluation and field study resulted in a final list of sites examined in detail in this project. Table 39 lists the final field study sites, detailing where project personnel undertook in-person evaluations or collected data, including those locations where only photographs were collected.
TH 62 = State Trunk Highway 62; UAV = unmanned aerial vehicle.
[1] The Site Selection Report was an internal report submitted as a deliverable as a part of this project. This internal deliverable was submitted to FHWA in December 2014.