Superstreet Concepts & Application
Prepared by: PAPE-DAWSON ENGINEERS, INC. October 16, 2012
1 Purpose of a Superstreet • Improve Traffic Flow • Increased Safety • Economical Solution What is a Superstreet? • Innovative intersection improvement • Also referred to as a Restricted Crossing U-Turn Intersection (RCUT) • Minor street traffic turn right • Minor street left-turns and through required to U-turn downstream
Vehicle Movements Pedestrian Movements Safety Benefits Reduction in Conflict Points
Operational Benefits of Superstreets Per FHWA: • Superstreets can provide up to a 30% increase in throughput (vehicles exiting intersection per hour) • Superstreets can provide up to a 40% reduction in network travel time reductions
Capacity Benefits of Superstreets Loop 337, New Braunfles (Simulation Results) Where Are They Deployed? • Michigan - Median U-Turn (Michigan Left) intersections common; one RCUT intersection at Big Beaver Rd in Troy, MI • Maryland – Deployed primarily as a rural unsignalized safety treatment, called a J-Turn • North Carolina: • US 17 in Leland • US 17 in Pender County • SU 15-501 at Erwin/Europa Drive, Chapel Hill • US 1 near VASS, Moore County Source: Google Maps • US 74 west of Waynesville, Haywood County
Source: Google Maps Source: Google Maps Where Are They Deployed? • US 281 North, San Antonio Encino Rio to Marshall Rd • Loop 1604 West, San Antonio New Guilbeau to Shaenfield Rd • SH 71 at FM 973, Austin (Under Construction When Are They Appropriate? • High Major Street Volume • Low Cross Street Through Volume • For High Cross Street Volumes a Median U-Turn or (MUT) intersection may be applicable
• FHWA: Alternative Intersections & Interchanges: Informational Report (AIIR) • Minor Road Total Volume (MRTV)/Total Intersection Volume (TIV) Ratio • RCUT Throughput 15 to 30 percent higher than Conventional when MRTV/TIV Ratio is 0.1 to 0.2 • Conventional Throughput 5 to 17 percent higher than RCUT when MRTV/TIV ratio greater than 0.25
Design Parameters Turnaround Location • 400 – 1,200 ft from intersection • AASHTO: 400 – 600 ft spacing for Median U-Turn • MDOT: 660 ft as standard spacing • NCDOT: 800 ft minimum
• Considerations in Placement • U-turn Queue Storage • Signal Timing • Driveways • Travel Time
Design Parameters Channelization • Left-Turn Lanes and Central Islands
• Triple Right-Turn Lanes
Median U-Turn Intersection: US 281 at Encino Rio • Triple left-turn from Encino Rio Design Parameters Turnarounds • Two-Lane Turnaround Design Vehicles
PP
WB-62 Accommodates truck off-tracking Design Parameters Turnarounds • Minimum Median Width: (Including turnaround lanes) • 4-Lane: 62 ft • 6-Lane: 40 ft • Minimum ROW required at Turnarounds for WB-62. • 4-Lane: 155 ft (nominal) • 6-Lane: 165 ft (nominal) Design Parameters Turnarounds 110’
40’ MIN Signalization
• Source: Alternative Intersection/Interchange Report 18
Signalization Signal Control
• One Controller • Both major street approaches and turnarounds • Two Controllers • One for each direction on major street, controls intersection and turnaround for same direction • Four Controllers • Each direction of major street and turnaround operated by a separate controller • Simple Operation
Signalization Vehicle Detection • High Speed Major Roadway • Advanced Radar Detection • Presence Detection • Radar • Video
Signalization Pedestrian Considerations • ADA Path • Audible Pedestrian Signals • Navigate complex intersection
Signalization Turnarounds • Turnarounds treated like left-turn phases • Under lower volume conditions, turnarounds could be unsignalized
Need for Additional Through Capacity • Approximate Major Street Capacities: • 700 to 900 veh per hour per lane (conventional) • 1,250 to 1,350 veh per hour per lane (superstreet) • Efficient signal phasing leads to increased green time. • 1,800 veh per hour per lane uninterrupted flow • Throughput at intersections can be increased with Auxiliary Through Lanes (ATL) • A four lane road with an ATL in each direction could conceivably carry 3,750 veh per hour (1,250 x 3) in one direction through a superstreet intersection • Used on Loop 1604 at Shaenfield • ATL utilization can be improved with increased upstream storage length and downstream merge distance (Not supported by NCHRP 707)
Need for Additional Through Capacity • Loop 1604 Auxiliary Through Lanes at Shaenfield Rd 1,000’ Merge 2,200’
1,000’ 1,400’ Questions