I-215 and Keller Road Interchange
Cal Poly Pomona Senior Project
The benefits of the Single Point Urban Interchange are its relative compactness and lower right-of-way requirements. This alternative requires a bridge replacement to be able to accommodate the four left-turn ramps under the bridge. Just as we did with the previous alternatives, we maintained the existing profile of the I-215. We re-graded the local road to meet the 15-foot minimum vertical clearance for the bridge and maintain positive drainage.
To improve the flow of traffic, the SPUI is designed with free right-turn lanes. The SPUI is a viable alternative because it is more efficient than tight diamond interchanges in handling large volumes of left-turn traffic and there will be a high volume of left-turn traffic on the southbound off-ramp.
Single Point Urban Interchange (SPUI)
Traffic Analysis
Synchro 9 and SimTraffic were used to model and analyze the intersection. Synchro analyzed the Level of Service (LOS) at each intersection using HCM methodology and presented the LOS at the intersection for both AM and PM peak hours. All right-turn movements are yield control and all left-turn movements meet at a single intersection.
Result: Pass
C/D
Geometric Feasibility
This step involved a rough design for the Single Point Urban Interchange. Due to its relative compactness and efficiency in handling high traffic volumes compared to a standard diamond interchange, we determined that the interchange would be able to provide the capacity determined in the Synchro analysis with minimal impacts to the existing right-of-way. 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 Single Point Urban 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 geological impact report will also be needed for this alternative because the design is located in an area that is susceptible to landslides. A portion of land with a high potential for paleontology resources goes through the SPUI 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 need to be constructed as well 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.
Merge/Diverge Analysis
B
B
D
D
Geometric Design
The benefits of the Single Point Urban Interchange are its relative compactness and lower right-of-way requirements. Referring to the guidance provided by Caltrans, the right-of-way requirements for SPUIs and tight diamonds are similar. Since SPUIs are not common in California, it was ranked low in the driver expectation category of the weighted decision matrix, which can be found under Project Deliverables.
This alternative requires a bridge replacement to be able to accommodate the four left-turn ramps under the bridge. As done with the previous alternatives, the existing profile of the I-215 was maintained. The local road was re-graded to meet the 15-foot minimum vertical clearance for the bridge and maintain positive drainage.
To improve the flow of traffic, the SPUI is designed with free right-turn lanes. The SPUI is a viable alternative because it is more efficient than tight diamond interchanges in handling large volumes of left turn traffic and there will be a high volume of left turn traffic on the south bound off ramp.
However, due to the compact nature of the SPUI, it would be difficult to modify the intersection for future growth past its original design life. Also, bicycles are typically difficult to accommodate in the traffic lanes or shoulders without adversely affecting the operational efficiency of the SPUI due to their slower speeds.
The complete Geometric Approval Drawing for the SPUI can be found under Project Deliverables.
The typical cross section shown has 8-foot bike lanes and 8-foot sidewalks. The median serves as a left turn pocket to enter the highway.
Advance Planning Study
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 SPUI alternative, a new bridge design is needed but unlike the other two alternatives with single span bridges, this one requires a three span bridge due to the interchanges structural configuration. The middle span length would stay at an extended 150 feet, and the two additional spans on each end are ¾ of that length at 112.5 feet. The other distinguishing factor of this bridge to consider, compared to the Roundabout’s layout, is that in order to provide sufficient support for the bridge itself, hammerhead pier columns were decided to be placed directly underneath each end of the middle span, as shown in the cross section and elevation view. The pre-cast California wide flange girder section type stays the same. Also, for this alternative, the sloped paving on the sides were kept instead of the cantilever walls so as to not incur any additional unnecessary costs in construction since there are no elements of concern in the empty spaces on each end of the bridge for this design.
Viability
The Single Point Urban 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. All documents and deliverables pertaining to this design can be found under the Project Deliverables tab.
