ALTERNATIVE #2 - SPREAD DIAMOND

Lamb Canyon (South)

OVERVIEW

The Spread Diamond Interchange will connect SR-79 to Lamb Canyon Landfill while limiting Right-of-Way (ROW) and environmental impacts. This design alternative meets driver expectations and provides familiarity to constructors and drivers alike. The Spread 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 spread diamond ramp design will have two intersections. For SB intersection, the 2025 AM/PM LOS is A/A and the 2045 AM/PM LOS is A/A. For NB intersection, the 2025 AM/PM LOS is A/A and the 2045 AM/PM LOS is B/B. These results satisfy the minimum LOS requirement of D as set forth by Caltrans standards.

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GEOMETRIC FEASIBILITY

The Spread Diamond Interchange provides access to Lamb Canyon Road from the realigned SR-79. The design incorporates two on ramps and two off ramps with signal control at the east and west sides of Lamb Canyon Road. The proposed alternative decreases traffic accidents and promotes traffic flow by utilizing a bridge median and two to one ramp transition lanes for the northbound on ramp. The design alternative accomadates for future traffic congestion and is a practicle design.

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ENVIRONMENTAL IMPACT

The Spread Diamond Alternative is a newly design intersection that allows for limited impacts to 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. This alternative causes the second highest right of way impacts for Lamb Canyon Road. 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 Spread 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 Spread Diamond will provide a four-foot (4) shoulder, twelve-foot (12) travel lane, and another eight-foot (8) shoulder The northbound off and on ramp features a two to one transition lane. The ramps will be constructed with a 2% negative grade in order to facilitate drainage throughout the interchange.

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VIABILITY

The Spread Diamond Hybrid was deemed viable upon examination of the design's Traffic Analysis, Cost Analysis, Environmental Analysis, and Geometric Design Analysis. The alternative would be sufficient in reducing congestion and determined to improve freeway conditions. All documents and delivers for the design can be found within the Project Deliverables tab.

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