HALF TIGHT DIAMOND INTERCHANGE

We wanted to look and see if providing a ½ tight diamond interchange would accommodate the needs of our project, as shown previously. 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.

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This design implements a grade separation along State Route 2 which allows for continuous movement in both directions along State Route 138.  The addition of dedicated off-ramp lanes for westbound 138 creates a significant increase, we effectively eliminate the potential for seasonal traffic to cause back-up and create another bottleneck situation.  When the design is put into the traffic modeling software Synchro, the signalized intersection at the top of the grade separation shows an A-rating for level of service, which is a measurement of the delay it causes.  This means the interchange improves operations and accommodates 2045 traffic volumes for both AM and PM peak hours. Lastly, the design improves sight distance issues and conflicting points from the existing intersection, which will greatly reduce the chances of accidents caused by speeding, failure to yield, and improper turns.  

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The half-tight diamond layout addresses all of the needs of this project, while simultaneously reducing greenhouse gas emissions, providing better access for emergency service vehicles, and increasing comfort speed for State Route 138.

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For this design, we created a GAD and an APS which both can be found under Project Deliverables.