DDI : The Ops ExperienceA Region 3 Perspective
DDIs in Region 3• American Fork
– Pioneer Crossing and 500 E– Purpose built – Work great– Run free
DDIs in Region 3• Timpanogos Highway (SR-92)
– Retrofit DDI – Under the freeway– Was opened with less than designed lanes– Works great (most of the time)– We’re retrofitting a trail into the DDI
DDI Operational Modes• Excess Capacity Mode (Low V/C ratio)
– Run the intersections uncoordinated– Snappy response on detection– Low investment in timing – spend efforts on
best possible detection– Low delay – easy to operate– American Fork DDIs
DDI Operational Modes• Design volume mode (moderate V/C ratio)
– Run the intersections coordinated– Coordination is relatively easy– Low delay – fun to operate – Timpanogos Highway
DDI Operational Modes• Near Capacity Mode (high V/C ratio)
– Coordination is crucial, difficult and time consuming
– Interchange may “lock up”– Small changes = big delays– Large through movements are a problem
Observations• DDI vs. SPUI
– Power out/Flash operations DDI is better– Off-peak operations DDI is better– Overcapacity ops – SPUI is better– Frontage road spacing – SPUI is better– Pedestrians – DDI works great with center
sidewalk
Observations• With both intersections
on same cabinet: – Diagram in cabinet
shows indications– Camera Access in
cabinet
Indicators show which lights are
on
Pedestrians• Timpanogos Highway
– Adding trail to south side of interchange– Not impossible – but would be better in center– Adding peds on side rather than center can
drive a decision to add a second controller and cabinet.
Acknowledgements• Eric Rasband and the I-15 CORE team
• Matt Luker and the UDOT Traffic Management Division
• Further Reading:– UDOT Diverging Diamond Interchange (DDI) Observations &
Experience, Eric Rasband, Taylor Forbush and Kelly Ash
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