ALTERNATIVE #1 - TIGHT DIAMOND

Lamb Canyon (South)

OVERVIEW

The Tight Diamond Interchange will connect SR-79 to Lamb Canyon Landfill while limiting Right-of-Way (ROW) and environmental impacts. This design alternative is a simple and common design that provides familiarity to constructors and drivers alike. The Tight Diamond will provide on and off ramps for both Northbound and Southbound traffic while producing maximum sight distance for drivers.

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TRAFFIC ANALYSIS

The traffic team performed a traffic analysis for this alternative using Trafficware Synchro 10 to evaluate the number of approach lanes and level of service. Peak hour traffic volume data was obtained from Caltrans Traffic Counts Census, Riverside County Traffic Analysis Model (RIVTAM) and Southern California Association of Governments (SCAG) Model. The annual growth rate for traffic volumes for 2025 and 2045 were forecasted using Caltrans 2017 Transportation Concept Report. The tight diamond design will have two intersections. For the SB intersection, the 2025 AM/PM LOS is A/A and the 2045 AM/PM LOS is A/A. For the NB intersection, 2025 AM/PM LOS is A/A and the 2045 AM/PM LOS is A/A. These results satisfy the minimum LOS requirement of D as set forth by Caltrans standards.

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GEOMETRIC FEASIBILITY

The Tight Diamond Interchange consists of providing on and off ramps with access to Lamb Canyon Road from the realigned SR-79. This alternative utilizes signal controlled stop lights at ramp termini in order to facilitate traffic flow and reduce congestion and traffic accidents. This design alternatives accomodates expected traffic congestion increase and is a viable interchange alternative for Lamb Canyon Road.

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ENVIRONMENTAL IMPACT

The Tight Diamond Alternative is a simple design that allows for the least amount of right of way impacts for Lamb Canyon Road and the conserved land west of the SR-79. The Mutiple Species Habitat Conservation Plan (MSHCP) land and Public Quasi Public Conserved (PQP) land are located along the Southern portion. They are habitat to multiple endangered and threatened species and rare plants. Some of the species included is the Stephan Kangaroo Rat, the Los Angeles pocket Mouse, and the California Satintail. Proper mitigation techniques such as relocation of a species are thought to be the best tactic not only ensure the completion of this project, but also the safety and prosperity of the species. In addition, to the project site rolling terrain condition, the introduction to retaining walls were introduced. Also, this alternative requires utility relocation. Lastly, proper drainage will be implemented in the design and a Storm Water Pollution Prevention Plan as outline by the Riverside County Flood Control and Water Conservation District.

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DETAILED DESIGN

The Tight Diamond Interchange design will provide two (2) twelve-foot (12) lanes and one (1) four-foot (4) shoulder for each travel direction (East & West). These travel lines will be separated by a four-foot (4) median in the center of Lamb Canyon Bridge. The on and off ramps for the Tight Diamond will provide a four-foot (4) shoulder, twelve-foot (12) travel lane, and another eight-foot (8) shoulder. The ramps will be constructed with a 2% negative grade in order to facilitate drainage throughout the interchange.

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VIABILITY

The Tight Diamond Interchange was one of three design alternatives considered for final design selection for the intersection at Lamb Canyon Road. This alternative design has been analyzed through a Cost Analysis, Traffic Analysis, Environmental Analysis, and Geometric Design Viability. It has been determined to improve freeway conditions and provide a viable alternative to the intersection at Lamb Canyon. All documents and delivers for this design can be found under the Project Deliverables tab.

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