I-215 and Keller Road Interchange
Cal Poly Pomona Senior Project
The hybrid diamond interchange is an innovative interchange which combines the compact diamond and spread diamond configurations. The Geometric Team came up with this design after dealing with right-of-way constrictions due to the ongoing construction of the Kaiser Permanente Hospital and local businesses in the area. It takes the layout of a conventional diamond interchange with two on-ramps and two off-ramps.
Hybrid Diamond Interchange
Traffic Analysis
Synchro 9 and SimTraffic were used to model and analyze the intersections. Synchro analyzed the Level of Service (LOS) at each intersection using HCM methodology and presented the LOS at the Northbound and Southbound intersections for both AM and PM peak hours.
Result: Pass
C/D
B/C
Geometric Feasibility
This step involved a rough design for the hybrid diamond interchange. By designing a hybrid configuration with spread diamond ramps west of the freeway and compact diamond ramps east of the freeway, we determined that the interchange could be laid out within the existing right-of-way and undeveloped land, while still providing the capacity determined in the Synchro analysis. As this alternative is still considered viable, we may proceed to the next step in the selection process.
Result: Pass
Impact Evaluation
The possible negative impacts of the Hybrid Diamond Interchange to the surrounding area were evaluated in this step. The design goes through an undetermined flood hazard zone; therefore, a flood hazard analysis will need to be conducted. A portion of land with a high potential for paleontology resources goes through the Hybrid Diamond design boundary. This means that a Paleontology Identification Report needs to be done in the northeast portion of the site. The drainage at the site needs to accommodate additional stormwater runoff since pavement will be added at the site. Soundwalls will also need to be constructed as the design is located near two noise sensitive receptors. This alternative is still considered viable at this point and will move on to the next step in the selection process.
Result: Pass
Detailed Design
A Merge/Diverge Analysis is an examination of the impact a ramp is expected to have at freeway-ramp junctions. The methodology provided in the HCM 2010 was followed for this analysis. The analysis procedure first involves computing the demand flow rate immediately upstream of the merge (on-ramp) area or diverge (off-ramp) area. The capacity of merge/diverge area was compared to the demand flow rate; if the demand is greater than capacity, then the LOS for the ramp-junction is F. If not, the density was then computed and the LOS was determined accordingly. Failing LOS indicates that the length of the merge/diverge ramp is inadequate. However, since the nearest adjacent interchange next to this project location is only 1 mile north of Keller Rd, auxiliary lanes must be added as per the Caltrans Highway Design manual between the Scott Road and Keller Road Interchanges. Shown below is the LOS obtained from the analysis.
B
B
B
B
Merge/Diverge Analysis
Geometric Design
The Geometric Team came up with the Hybrid Diamond design after deciding that the eastern ramps were constricted by right-of-way due to the ongoing construction of the Kaiser Permanente medical facility and local businesses in the area. To accommodate for this, it was decided to use the layout of a compact diamond. By using a compact diamond layout, the ramps would use less area and will not interfere with the Kaiser Permanente medical facility, nearby businesses, and local residents.
On the west side of the I-215, there was more generous room to work with as there was more undeveloped land. It was thus decided to use the layout of a spread diamond. By utilizing the layout of a spread diamond, plans can be made for an increase in population in the area while also reserving the land for an additional loop ramp if needed. This spread-out design also provides for more storage room between the intersections and helps to alleviate congestion. Thus, the final design is called a Hybrid Diamond because it makes use of both a compact and a spread diamond.
The cross section of Keller Road was also modified underneath the bridge to ensure continuity with the Keller Road corridor. This cross section includes new sidewalks, shoulders with bike lanes, and 2 additional lanes in both directions. This was possible by changing the side slopes underneath the bridge into cantilever walls.
The complete Geometric Approval Drawing for the Hybrid Diamond interchange can be found under Project Deliverables.
APS, or Advance Planning Studies, are required in Project Study Reports and Project Reports to document the scope and cost of structure work in projects. They consist of one plan sheet for each structure showing the basic layout details and cost estimate. Typically APS must be prepared for all structural work including bridges, culverts, tunnels, retaining walls, and any non-standard or special design structures. It helps decide on a feasible structure type, requirements, constraints, and an associated cost estimate summary for the structure work involved. For this project, the only major structure within the scope of the project is the bridge which lies at beneath the I-215 freeway at the intersection with Keller Road. From current conditions, the existing bridge at this location is below the minimum 15-foot vertical clearance from Caltrans bridge design aid requirements.
For the Hybrid Diamond alternative, fortunately, a new bridge or any other drastic changes will not be done to the existing structure due to the alternative’s geometric design layout. However, the three elements of concern with this APS are ensuring that the 15-foot vertical clearance is met, and that the width of the existing bridge is extended due to the widening of the I-215 in each direction as noted previously. The existing pre-stressed concrete box girder remains the same. Also, as shown in the elevation view, instead of having sloped paving on the sides we opted to have straight cantilever walls.
Advance Planning Study
Viability
The Hybrid Diamond Interchange went through all steps done while reviewing possible alternatives - Alternative Scoping, Traffic Analysis, and Geometric Design. It was considered as one of the three viable alternative design through all of the aspects mentioned in detail above. It also passed the traffic analysis, geometric feasibility, and impact evaluation steps and was considered viable for detailed design. It was ultimately chosen as the team's recommended alternative interchange design based on the Weighted Decision Matrix. All documents and deliverables pertaining to this design can be found under the Project Deliverables Tab.
