Ord 1423 (2) - Laserfiche WebLink

Home Browse Search

Selection of Preferred Alternative The process of selecting a preferred design alternative for the Aurora Donald Interchange started with an initial set of 20 different interchange design concepts that was reduced to 9 concepts after a fatal flaw analysis. (See TAMP Chapter 4 Concept and Alternatives Development.) After further study and review by ODOT Region 2 and continued design refinements, two interchange design alternatives emerged: Single Point Interchange and Diverging Diamond Interchange. ODOT conducted stakeholder and public engagement to vet the two alternatives, ultimately selecting the Diverging Diamond Interchange (DDI) as the Preferred Alternative based on performance and public and stakeholder feedback. The DDI Preferred Alternative is also known as a double crossover diamond interchange (see the Refined Preferred Alternative in TAMP Figures 5-3 and 5-4). In a DDI interchange configuration, traffic on Ehlen Road crosses to the opposite (left) side of the road while within the interchange footprint (i.e., between the ramp intersection traffic signals). Dual traffic signals at the ramp intersections control the movement of traffic during this crossover maneuver. Upon reaching the second traffic signal, vehicles are returned to driving on the right side of the road. The DDI allows signalized ramp intersections on Ehlen Road to operate in a more efficient manner, as two-phase traffic signals. The DDI will improve safety because there are no left turns across opposing traffic and most turning movements are controlled by signals. Another safety and traffic operation benefit is that left and right turns can occur simultaneously. The Preferred Alternative would construct one new 1-5 bridge to carry north- and southbound traffic over Ehlen Road.The new I-5 bridge would require reconstruction of the 1-5 travel lanes to attain additional vertical clearance over Ehlen Road and would move the 1-5 southbound lanes east, into the median to align with the new bridge structure. Realignment of Ehlen Road west of 1-5 would also be required to create the desired approach angles for the crossover intersections. Bents Road and Dolores Way would both be realigned to improve sight distances and intersection spacing, while allowing full access to the adjacent businesses. TAMP Figure 5-3 shows the refined Preferred Alternative; Figure 5-4 shows a cross section of the 1-5 bridge over Ehlen Road. Phasing of the DDI Preferred Alternative is needed to accommodate funding allocated in the Keep Oregon Moving Act. This funding represents a substantial down payment towards fully implementing the Preferred Alternative but does not cover the full cost of the interchange as designed. As a result, an initial Phase 1 project was developed. The primary objective of the Phase 1 project is to improve safety and operations by keeping the interchange off-ramp vehicle queues out of the portions of the ramps needed for safe deceleration from 1-5 mainline speeds or onto the 1-5 mainline itself.The extended lengths of the off-ramps and capacity improvements at the ramp intersections allow vehicle queues to be safely stored on the off-ramps. Phase 1 is focused on protecting the interchange operational area west of the interchange along existing Ehlen Road through an improved Ehlen Road/Bents Road/Bents Court intersection. ODOT will also purchase access control along Ehlen Road between this access point and the southbound ramps. On 1-5:Aurora Donald Interchange(Exit 278)TAMP:Supporting Findings for Marion County Adoption 2