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Geometric Design

Scope

The scope of design work for this improvement project was to create preferred alternative plans from the collection and analysis of existing site conditions and detailed consideration of future development. This analysis provided emphasis on Railroad Canyon Road's existing geometric constraints due to local commercial development as well as standardization or improvement of deficient intersection spacing existing at the site. Once developed, these project plans will include alternative horizontal geometry and alignments, along with associated vertical profiles. These plans were then used as a vital resource in the analysis of alternative cost estimations and potential environmental impacts. Comprehensive Geometric Approval Drawings (GAD) include new or altered roadways within the project design area, superelevation diagrams for all interchange elements, and typical road cross-sections in addition to those design elements listed above. Final GADs are to be included with the Project Study Report (PSR) and submitted to Caltrans and The City of Lake Elsinore.

Existing Conditions and Constraints

Railroad Canyon Road has proven to be a significant concern for the rapidly growing city of Lake Elsinore. Unfavorable intersection configuration and limited interstate access to the city has plagued Railroad Canyon Road with persistent operational failure. These deficiencies have adversely effected overall mobility for city residents and visitors alike. Additional concerns have been raised as continued interchange degradation will negatively impact the Interstate 15 freeway corridor traveling through the city.

Railroad Canyon Road's existing conditions and constraints are highlighted in the video above. Intersections displayed above represent critical circulation elements which provide access to the city's recreational activities, local business market and access to the Interstate 15.

Alternative Consideration

Preliminary engineering was conducted in order to generate a set of conceptual alterative designs. These alternatives were considered as reasonably viable in relation to the general purpose and needs of this improvement project. From a design perspective these needs involved the evaluation of existing severe geometric constraint, right of way acquisition and intersection spacing within our project design boundary. Existing geometric design implores tight configurations with adjoining local frontage roads and movements on and off the interstate. Railroad Canyon Road services six local frontage connections and four interchange ramps within a distance of just over a quarter mile. Additional geometric consideration included environmentally sensitive areas such as the San Jacinto riverbed just north of the existing interchange and local hydrological impacts which inhibited design extents. Right of way acquisition was also limited as the existing interchange is utilized as a major source of mobility to and from the city. This naturally cultivates high density commercial development in close proximity of the existing facility which proves difficult to relocate and can significantly impact proposed alternative cost. Due to the existing elements above, intersection spacing along Railroad Canyon Road lacks the capability of efficiently servicing vehicles traveling within the interchange. These existing features were extensively evaluated in the development of viable alternatives that would require additional in depth analysis. Considered project alternatives were thoroughly assessed using methods traditionally used in industry and included the following:

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  • Single Point Urban Interchange
  • Continuous Flow Interchange
  • Hook Ramp Variations
  • Roundabout Variations

  • Diverging Diamond Interchange
  • Split Diamond Interchange
  • Collector-Distributor/Frontage Road


  • Preferred Alternatives

    Following the completion of detailed traffic and geometric feasibility analysis, potential alternatives were selected that provided the highest degree of operational improvement. In addition to this multifaceted analysis, selected alternatives received comprehensive review to ensure the highest degree of standard was met. The use of AutoTURN for example, enabled the dynamic implementation of truck turning templates to all movements within the interchange. Geometric alterations were conducted to ensure adequate off tracking spacing of commercial truck trailers particularly on and off the interstate facility. Draft designs were then submitted to Caltrans top management for assessment utilizing a design checklist for evaluation of actual industry design. These standardized and final alternatives not only met project purpose and needs but were economically responsible and environmentally conscientious.

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    Diverging Diamond Interchange (DDI)

    The Diverging Diamond Interchange also known as DDI, is a relatively new interchange design and is beginning to become a forefront in design consideration for urban mobility. It incorporates the "braiding" of traffic movements which essentially diverts traffic to the opposing side of the roadway. While this may be unfamiliar to drivers, the operational advantages are numerous. This design effectively reduces traffic signaling to three phases instead of four allowing for continuous left turn movements onto the adjacent interstate facility, while extending through movement phases.

    This alternative was selected as a preferred design based upon it meeting or exceeding our project needs. Due to existing deficient intersections spacing, traffic phase reduction improves continuous mobility while decreasing delays invoked by inadequate queuing lengths of lanes. Additionally, high left turn movements experienced at the project site are allowed to move freely, eliminating excessive vehicle storage. In addition to these benefits, this alternative also limits significant alteration to existing road alignments and adjacent facilities which greatly reduce total project costs.

    Please click the following link to view/download mandatory design exceptions for this alternative. DDI Fact Sheet


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    Continuous Flow Interchange (CFI)

    The Continuous Flow Interchange also known as CFI, is also a relatively new interchange design. This design is similar to that of the Diverging Diamond, although instead of diverging all traffic, only the left turn movements travel to the opposing side. Just as with the Diverging Diamond, this design also reduces traffic signaling to three phases instead of four allowing for continuous left turn movements onto the adjacent interstate facility while extending through movements of approaching vehicles.

    This alternative was selected as a preferred design based upon it meeting or exceeding our project needs. Due to existing deficient intersections spacing, traffic phase reduction provides greater mobility while decreasing delays invoked by inadequate queuing lengths of lanes. As before, high left turn movements are allowed to move freely, eliminating excessive vehicle storage and mitigating potential traffic jams that often block upstream intersections. In addition to these benefits, this alternative also limits significant alteration to existing road alignments and adjacent facilities which also greatly reduces total project costs.

    Please click the following link to view/download mandatory design exceptions for this alternative. CFI Fact Sheet


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    Single Point Urban Interchange (SPUI)

    The Single Point Urban Interchange, also known as SPUI, has been gaining a reputation in recent years as these designs are being implemented on major facilities throughout California. Despite it's larger footprint than the previous alternatives, this design features the implementation of an interchange with a single point of intersection for all movements on and off the interstate facility. This is in stark opposition to traditional two intersection ramp configurations but offers improved mobility in areas of high geometric constraint. This single intersection offers traffic control for all ramps and local through movements and exceeds traditional interchange performance by allowing generally opposing turning movements to operate simultaneously.

    This alternative was selected as a preferred design based upon it meeting or exceeding our project needs. Due to existing deficient intersections spacing, this alternative would eliminate existing nonstandard spacing and provide the highest level of operation for this project. This is achieved by the removal of short storage lanes for vehicles and provide adequate phasing for high left turning movements on and off the interstate during AM and PM peak hours. Additionally, this design will provide alterations to the existing Interstate 15 overcrossing which will comply with the future build out and extend the structures design life.