DDIs – State of the Practice and the Next Evolution

1 DDIs State of the Practice and the next EvolutionSmith SiromaskulOVERVIEWCONCEPTUAL OVERVIEWDDI Sites Used for high volumes of turns Typically requires fewer lanes Possibly costs less Generally looks coolTHE BIG PICTUREA WORD OF WARNING Concept to 15% DesignNON- PERPENDICULAR CROSSING ANGLE Crossroad alignment driven by structure cost No need to achieve a perpendicular crossing can mean MUCH less right-of-way with a DDIP ioneer Crossing DDI IntersectionINTERIOR ANGLESIGNING AND PAVEMENT MARKINGSS igning & Pavement MarkingMonotubeOptionSigning & Pavement MarkingOverhead SignagePEDESTRIANS OUTSIDE TREATMENT Pedestrian Travel Paths Bicycle Travel PathsPEDESTRIAN TREATMENT Common Practice to keep pedestrians to outside Conflicts with left turn onto entrance ramp Unsafecondition with limited sight distanceNUniversity ParkwayPEDESTRIAN TREATMENT No conflict with left turns Barrier-protected sidewalk 80-90% public approvalNUniversity Parkway Significant pedestrian volumes are present Turning roadways have more than one lane To eliminate weaving issuesSIGNALIZED MOVEMENTSOFF RAMP RIGHT TURN OPTIONSC heyenne, WYCheyenne, WYFL LESSONS LEARNEDFL LESSONS LEARNEDM odelWest Ramp TerminalEast Ramp TerminalAM PeakPM PeakAM PeakPM next Evolution Splintered Diverging Diamond Interchanges Here s where it gets UPON A TIME IN FLORIDAEXISTING VOLUMESPROJECTED VOLUMESTYPICAL DDI LAYOUT-UNIVERSITY PARKWAY Median pedestrian treatment Pavement slope concerns Uncertainty of future volumesNUniversity ParkwayDIFFERENCES Existing (2012 counts) Design Year (2034)WHAT S NEARBYCHOOSING A DESIGN Need for excess capacity, within reason Mitigation for pavement sloping issues DDI VariantsColorado Springs, CO Three structures Three roadways (2 EB, 1 WB)

2 ADVANCED LEFT DDI SECLIN, FRANCEA dvanced Left Turn DDI / I-75 at SR 70 Sarasota, FLADVANCED LEFT TURN DDIS plintered DDI / I-75 at SR 70 Sarasota, FLKEY DIFFERENCESC olorado Springs, COSplintered DDI / I-75 at SR 70 Sarasota, FLVOLUME SCENARIOSFINDING FLAWS IN A DIAMONDS cenarioTypical DDIS plinteredDDIEB ThruSB LeftOverallEB ThruSB in seconds per vehicle through the entire interchange areaSUMMARYA dvanced left DDI Improves core lane utilization Separation of crossroad left queue Splintered DDI Large number of lanes Excessive internal queuing Left turns from ramps Unbalanced leftsBraided Splintered DDI / I-75 at SR 70 Sarasota, FLCONTACT INFORMATIONS mith Siromaskul, SW 5thAvenue #1800 Portland, OR