Interchange 5th Edition Level 2 Pdf

[Sabel Kantah]

Typicallysubstantiated information comes by way of Interchange Justification Reports (IJRs). IJRs are written early in the project planning process, with details generally consistent with conceptual design and descriptions of potential safety performance impacts.

In 2009, FHWA began collaborating with the Transportation Research Board to develop the Enhanced Interchange Safety Analysis Tool (ISATe), an improved prediction methodology and safety analysis tool for corridor and site-specific analysis. ISATe also provides information about the relationship between roadway geometric design features and safety. This version of the tool automates a safety prediction method consisting of algorithms and equations. The lead researchers of ISAT and ISATe worked as the lead researchers in the development of the Highway Safety Manual (HSM). Hence, many of the methodologies used in the interchange safety tools are adopted in HSM.

As an alternative approach to using ISATe during the planning phase, particularly for interchange configurations not considered in the existing tool, analysts can use a single crash modification factor (CMF) to assess the difference in expected safety performance from one interchange configuration to another. Unlike HSM models, a single CMF fails to capture complex interactions taking place and cannot be used to evaluate factors within an interchange configuration that may impact safety performance. However, this is a reasonable approach given what is known at the planning stage of a project.

While ISATe filled a critical need, analysts identified several difficulties in utilizing the tool. When funding became available in fiscal year 2020 to support the need for substantive safety performance assessments for IJRs, FHWA began developing planning-level models and tools to predict crash frequency and severity for an existing or proposed interchange. Published in early 2023, these planning-level models now allow analysts to compare the potential safety performance effects of freeway access and interchange design decisions earlier in the project development process without knowing the geometric details.

The research team surveyed FHWA division representatives for all 50 States, plus Washington, D.C., and Puerto Rico, to identify how commonly each interchange configuration is considered or constructed in each State, city, or territory annually. The survey included a graphical representation of potential interchange configurations to choose from, in order of importance or value to the State.

FHWA representatives from 47 divisions responded to the electronic survey, providing detailed descriptions of practices and information on access proposals received over the past few years in their respective locations. The results of the survey indicated the following configurations should be included in the next improved version of the predictive tool for interchanges (in order of most to least responses):

Additionally, this survey revealed the need to differentiate single roundabout interchanges from diamond interchanges with roundabout ramp terminals, otherwise referred to as roundabout diamond interchanges. The development of the new Interchange Configuration Safety Comparison Tool included roundabout diamond interchanges.

The method underlying this tool separately predicts fatal, injury, and property damage-only crash frequency. When combined, the tool predicts the total crash frequency for each interchange configuration considered. Moreover, the tool includes inputs to evaluate the relationship between geometric and operational features on the predicted severity level of injury crashes. Analysts can use the tool to evaluate the predicted crash frequency for varying interchange configurations, considering a standard diamond interchange or compressed diamond interchange as the baseline.

The predictive models underlying this tool identify that the relative safety performance among interchange configurations differs as the freeway volume per lane, crossroad volume per lane, or interaction of freeway volume to ramp volume changes. This means that for a given set of conditions, the relative safety performance among interchange configurations is different than an alternate set of conditions (i.e., a single CMF would provide misleading results of relative safety performance).

Additionally, this tool includes adjustment factors for planning-level geometric and operational characteristics that will impact injury severity, given that a crash has occurred. Considerations impacting crash severity include:

The FHWA research team developed an implementation spreadsheet based on the predictive model. The implementation spreadsheet allows users to enter data for any or all applicable interchange configurations for simultaneous analysis. Users can enter the exact data for each alternative or enter specific features as needed.

The implementation spreadsheet provides the predicted property damage only, fatal and injury, total crash frequency, and a 95 percent confidence interval for each interchange configuration entered. Additionally, the implementation spreadsheet provides a graphic representation of the outputs for visual analysis. As a companion document, the Interchange Comparison Safety Tool User Guide gives practitioners details on input data requirements and examples of data elements required for applying the predictive model.

The development of the Interchange Configuration Safety Comparison Tool bridged a gap, attempting to strike a balance between the need to assess the safety implications of design-level details and those details that are generally known during project concepts and preliminary engineering. Further, this tool focused on considering the interactions between individual project elements, rather than using a building-block approach; however, the safety effects of some interchange components (e.g., ramp terminal control) were difficult to isolate.

This new tool focused on the service interchange configurations most considered in access modification requests and cannot be applied to unique interchange configurations or system interchanges. Future efforts should build on the foundations of this tool to incorporate more locations (to support identifying the safety effects of ramp terminal configuration and traffic control) and to incorporate more interchange configurations considered by agencies as viable alternatives during project planning.

Service interchanges are facilities primarily designed to facilitate vehicular traffic movements, and this tool is developed based on this reality. Although design elements can be implemented at such facilities to better integrate non-motorized traffic, the design thresholds, such as roadway grades, curvatures, and design sight-distances, already adopted for decades at such facilities, imply that there are limits of what can be done to accommodate non-motorized users. At high vehicular traffic facilities like service interchanges, it is better to completely separate non-motorized traffic from motorized traffic using micro tunnels, separated bridge decks, or light-weight overpasses as conduits for moving non-motorized users.

Currently, the concepts of Complete Streets, Safe System approach, or safe roads for all users (different ways of providing better safety for non-motorized road users) are getting more attention from top-level decisionmakers. As the Vision Zero policy gets implemented broadly and into real projects, facilities for non-motorized road users will be systemically planned, designed, and built out, and the mix between motorized and non-motorized traffic will gradually shift to a new (more stable and livable) balance. As a result, traffic crashes will also change to new patterns with stable outcomes for all modes of road users. During the transition period, the safe performance prediction models for different types of facilities should be updated periodically to reflect the new paradigm.

Wei Zhang, Ph.D., P.E., is a research highway engineer/intersection safety program manager with FHWA, specializing in innovative intersection designs and safety analysis. He has a doctorate in civil engineering from the University of Minnesota.

Scott Himes, Ph.D., P.E., is a highway safety engineer with an engineering consulting firm in Raleigh, NC, specializing in the development and implementation of HSM methods. He has a doctorate in civil engineering from Pennsylvania State University.

The Four Level Interchange (officially the Bill Keene Memorial Interchange) is the first stack interchange in the world.[1] Completed in 1949 and fully opened in 1953 at the northern edge of Downtown Los Angeles, California, United States, it connects U.S. Route 101 (Hollywood Freeway and Santa Ana Freeway) to State Route 110 (Harbor Freeway and Arroyo Seco Parkway). In 2006, the interchange was officially renamed in the memory of Los Angeles traffic and weather reporter Bill Keene.

The highway is a stack interchange that connects U.S. Route 101 to State Route 110. All movements are possible in this interchange between US 101, which crosses over SR 110, but not necessarily with surrounding roads, like Sunset Boulevard, which crosses SR 110 just northeast of the interchange. The interchange is located at Exit 3 of US 101 and Exit 24A of SR 110.

The four-level reinforced concrete structure was designed by a team of engineers and built by the James I. Barnes Construction Company. Although it was finished in 1949, it was not put into full use until the freeways it served were completed and opened on 22 September 1953. [2][3]

In July 2006, the freeway interchange was officially named in honor of Bill Keene, former KNX and KNXT traffic and weather reporter, although the new name is rarely used. Keene referred to the interchange as "The Stacks" and the "4-H Interchange". During the 1960s, Dick Whittinghill on radio station KMPC sometimes called it the Four Letter Interchange.[4]

The interchange was constructed as a stack interchange because surrounding buildings and terrain made construction of a cloverleaf interchange impractical. The construction of the interchange displaced over 4,000 people from their homes and cost $5.5 million ($50.7 million in 2023) - making it the most expensive half-mile of highway ever built at the time.[5]

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