DESIGN PROCESS

Our Design team examined the existing geometric related issues, which we identified as undesirable driving curves, as well as sharp vertical grades. These conditions reduce the maximum comfortable speed. Adding to the issues, the areas surrounding our location travel at higher rates and due to these design features, are forced to slow down as they reach the intersection. Which all in all create an uncomfortable driving environment.

These concerns on their own would negatively affect any conventional state highway, however, they are amplified at our site by the presence of the State Route 2 which interrupts any continuous flow along State Route 138.  

The design came up with 5 design alternatives for this project which are identified as:

1. No-Build: This alternative analyzed the traffic and environmental impacts of the intersection if no improvement was made to it. 

2. Continuous Green T-Intersection: This intersection provides continuous flow for westbound 138 traffic, realign both state routes to provide a 90-degree intersection, as well as increase the storage length for seasonal traffic by implementing 2 left lanes for left turn movements. However, this alternative was dropped as it was not able to address the through movement of eastbound 138 traffic, and ultimately not mitigating the purpose and needs of the project.

3. Half Tight Diamond Interchange: The final alternative that was chosen based on our weighted decision matrix. This interchange was determined to meet every need that our project has, including providing continuous movement for state route 138 through grade separation. This alternative was also able to address seasonal traffic with a two lane westbound off ramp. However, with this, the cost of this alternative would be increased at our location due to structures, earthwork, and r/w impacts.

4. Half Diverging Diamond Interchange: This design alternative replicate most of the design features that were present in the ½ tight diamond interchange with one key characteristic, that would allow the intersection of the westbound 138 traffic to be located on the westbound side of 138, increasing our storage length and providing “through like” movements at the intersection provided by the crossovers in this design.

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5. No-Mo traffic interchange: This design alternative provides continuous flow for all movements. One of the key features of this design was that it provides similar features of a Roundabout but resulted in no Intersection. However, due to preliminary design, we found that although this alternative would meet the purpose and needs of the project it also would require significant increases in cost and we determined that an in depth design of such facility would not be feasible as well as provide an over design for the issues this project aims to address, however, we decided to still keep the Alternative in our Benefit/Cost analysis, as well as our decisions making process.

Further detailed information about all of our design alternatives and our design process can be found in our Project Initiation Report (PIR) which can be found under our Project Deliverables. Or can be accessed through the button listed bellow.