ALTERNATIVE #2 - SPREAD DIAMOND
California Avenue (North)
The diamond interchange is a simple, commonly implemented design that allows traffic to easily access SR-79 through two intersections by making right/left turns. The new design will connect the unpaved road on the east side of SR-79, and transition to existing alignment on the west side without interfering with traffic on the freeway. Access roads will be provided to surrounding private properties from California Ave through Laird Rd. on the eastern side, and the newly implemented frontage road on the left side.
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 design will have two intersections. For SB intersection, the 2025 AM/PM LOS is A/A and the 2045 AM/PM LOS is B/C. 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.
The Diamond Alternative consists of converting California Ave to a skewed overcrossing that stretches above SR-79 . The new 4,500 ft realignment of California Avenue will merge into existing on both sides of the freeway. The ramps follow a simple diamond design creating two, four-way controlled intersections, 600 ft apart on the bridge. This alternative is feasible and suitable for future improvements to increasse capacity of the interchange.
The Spread Diamond Alternative right of way impacts were reduced slightly compared to the Hook Ramp Alternative. The skew bridge causes less impacts to the surrounding residential and vacant parcels. However, partial and full land acquisitions are still required with this alternative. Due to the project site rolling terrain condition, the introduction to retaining walls were introduced. The proposed alternative requires utility relocation. Continuing, 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.
The cross-section of California Ave. in the Diamond alternative will have a 6' sidewalk, a 4’ bike lane in each direction to improve access for all users, a 4' external shoulder, two 12’ through lanes, and a 12' median. Bike lanes and sidewalks were included in our bridge design to promote active mobility and accessibility for all modes of transportation. The ramps of this alternative consist of an 8' external shoulder, one 12' lane with auxiliary to provide additional capacity on the intersections, and a 4' internal shoulder.
For our project study report, an Advance Planning Study (APS) was done to define the scope of structure work and develop a reasonable cost estimate for budget purposes. APS consists of a plan sheet for each structure with basic dimensions and minimal detailing including the vertical clearance, span length, and structure type. Each plan sheet contains the plan, elevation, typical section view, and cost estimate of the structure. All these structures will be constructed out of precast concrete. The Bridge Design Aids were used for the design of the new bridges. Please refer to the Geometric Approval Drawing and Advanced Planned Study under the Deliverables tab for geometric details of this alternative.
The Diamond Alternative was carefully revised and evaluated based on multiple factors including: Alternative Scoping, Traffic Analysis, and Geometric Design. It was considered as one of the three viable alternatives as it satisfied all the categories mentioned above. It also passed geometric feasibility, and impact evaluation steps and was considered viable for detailed design. All documents and deliverables pertaining to this design can be found under the Project Deliverables Tab.