2016 ITE Mid-Colonial District Annual Conference Wilmington, Delaware Safety Evaluation at Innovative Geometric Designs Gilbert Chlewicki, PE Advanced Transportation Solutions April 18, 2016
WHY INNOVATIVE INTERSECTIONS & INTERCHANGES? Intersections are a safety concern, with the highest percentage of crashes and severity than any other roadway 2 Photo Source: Mark Doctor, FHWA element.
INTERSECTION SAFETY FACTS Angle crashes account for over 40% of fatal crashes at intersections 3
INTERSECTION SAFETY FACTS Left turn crashes account for over 20% of fatal crashes at intersections 4
INTERSECTION SAFETY FACTS Ped/Bike crashes account for 25% of fatal crashes at signalized intersections 5
INTERSECTION CONFLICT POINTS - VEHICLES Crossing maneuvers occur where vehicle travel paths cross one another, merging maneuvers occur where vehicles from one traffic stream enter into another, and diverging are located at points in which vehicles depart a traffic stream. 16 Crossing Conflicts Source: North Carolina DOT
INTERSECTION CONFLICT POINTS LEFT TURNS Every conflict point is affected either directly or indirectly by a left turn movement
INTERSECTION CONFLICT POINTS VEHICLES/PEDS Four vehicle/pedestrian conflicts per crossing Conflicts involving RTOR and permissive left turns can be particularly problematic 8
ROUNDABOUTS Lake Ozark MO (2014) 9
ROUNDABOUTS TRACK RECORD Measurable progress in last 10+ years, but still underutilized Effective at individual locations and in corridors Source: Jeff Shaw, FHWA Proven in both low-speed urban and high-speed rural settings Can complement other improvements such as Access Management 78-82% Reduction in Severe Crashes 1 Source: Jeff Shaw, FHWA 1. AASHTO Highway Safety Manual, Chapter 14
ROUNDABOUTS ELIMINATE THE CROSSING CONFLICT POINTS
Essentially, roundabouts have Right-In and Right-Out movements WHY ARE ROUNDABOUTS SAFER?
COMPARISON OF VEHICLE / PEDESTRIAN CONFLICTS 16 Conflicts 8 Conflicts Source: NCHRP Report 672
SUPERSTREET/ J TURNS DISTINGUISHING FEATURES Cross street (minor road) traffic turns right, then accesses U-turn to proceed in desired direction. Main and U-turn intersections can be either signalized ( Superstreet ) or not ( J-Turn ) 14 Source: Wisconsin DOT
DIVIDED HIGHWAY WITH OPEN MEDIAN Problem: Far-Side Right-Angle Collisions 15
CONFLICT POINTS Traditional Intersection: 32 Conflict Points 16 Crossing Conflicts 20 Conflict Points True apple to apple comparison, J-Turns only has 10 and 16 superstreets only has 8 conflict points with just 2 crossing CPs
PEDESTRIAN-VEHICLE CONFLICT POINTS Conventional Intersection 24 conflict points Superstreet / J-Turn Intersection 8 conflict points 17
J-Turn Intersection Maryland Field Evaluations J-Turn versus conventional: Crashes decrease between 28% and 44% 1 1. Field Evaluation of a Restricted Crossing U-turn Intersection (FHWA-HRT-11-067) 18
NORTH CAROLINA STUDY Fatal and injury, angle, and leftturn crashes decreased by more than half following J-Turn installation Sample included 13 J- Turn intersections across the state where a two-lane rural minor road (STOP control) intersects a four-lane high-speed (55 mph) major road
J-Turn Intersections Tennessee Implemented J-Turn designs at 4 sites Before: 54 crashes (2 fatalities, 8 injuries) After: 10 crashes (0 fatalities, 0 injuries)
MODOT Performance Evaluation Analysis of 5 sites converted to J-turns Safety Benefits: 35% total crash reduction 54% reduction in fatal & injury crashes None of the five sites had a fatal crash following J-turn implementation In a public survey regarding trip time perceptions resulting from the J-turn, the majority said there was no adverse effect
J-Turn / Superstreet Crash Modification Factors J-Turn All Crashes Edara (2013) CMF = 0.652 (MO) Inman (2012) CMF = 0.56 (MD) Hummer (2010) CMF = 0.54 (NC) Fatal / Serious Injury Edara (2013) CMF = 0.46 (no fatals) Hummer (2010) CMF = 0.37 Superstreet: - Not enough years of open suburban / urban superstreets for CMFs yet - National CMF likely by 2018/19
MUT Median U Turn (aka Michigan Left) At-grade intersections with indirect left turns using a U-turn movement in a wide median and/or loon The MUT eliminates direct left turns on both intersecting streets, reducing the number of signal phases and conflict points at the main intersection 23
MUT LEFT TURN FROM MAJOR ROAD Vehicles on the major street (or the street with the median) that want to turn left are directed through the main intersection to a U-turn movement at a downstream directional crossover (usually signalized), and proceed back to the main intersection to then turn right onto the minor street.
MUT LEFT TURN FROM MINOR ROAD Vehicles on the minor street that wish to turn left at the major street are directed to turn right, make a U-turn movement at the same crossover, and then proceed through the main intersection.
VEHICLE-VEHICLE CONFLICT POINTS Crossing conflicts reduced from 16 to 4 Merging and diverging conflicts are each reduced from 8 to 6
PEDESTRIAN-VEHICLE CONFLICT POINTS At a MUT, the left turns are removed from the main intersection (and shifted to the U-turns located away from the intersection), thus removing pedestrian exposure to left-turning vehicles. MUT Intersection 16 conflict points Conventional Intersection 24 conflict points Although the number of pedestrian conflict points at a MUT is reduced, since leftturn demand movements are consolidated into right-turn movements, the total number of vehicles crossing the crosswalk is the same. Consideration of treatments such as a Leading Pedestrian Interval or right turn on red (RTOR) prohibitions may mitigate the conflicts. 27
SAFETY PERFORMANCE STUDIES CRASH RATE VALUES, NOT CMF! MUT intersections show safety performance improvements compared to conventional intersections for most crash types and injury severities. Source: FHWA Median U-Turn Informational Guide
Displaced Left Turn (DLT) Intersection CONTINUOUS FLOW INTERSECTION (CFI) Distinguishing Feature: Left-turn movement (on one or more approaches) strategically relocated to the far-side of the opposing roadway via interconnected signalized crossover in advance of the main intersection SR 30 and Summit Rd in Fenton, MO Source: Bing 29
PARTIAL CFI CONFLICT POINTS Every displaced left removes one conflict point and relocates three conflict points away from the main intersection. 30 Conflict Points 32 Conflict Points 30
CFI Crash Modification Factors CFI All Crashes Zlatkovic (2015) CMF = 0.877 (UT) Standard Deviation +/-4.6% Not officially rated yet, but likely to be between and
DIVERGING DIAMOND INTERCHANGE -DDI DDI with center-running light rail at I-494 and 34th Avenue in Bloomington, MN 32
CONFLICT POINT COMPARISON 33
OUTSIDE VS. INSIDE PEDESTRIAN PATHS Outside Walkway With transverse crossing Center Walkway 34
EARLY CONCERNS Will it? Cause driver confusion Cause pedestrian confusion Have many wrong-way movements Not accommodate trucks or emergency vehicles Work when the power goes out Work when it snows 35
DDI Crash Modification Factors DDI All Crashes Edara (2015) whole interchange CMF = 0.592 (MO) Edara (2015) ramp terminals CMF = 0.466 (MO) Fatal / Serious Injury Edara (2015) whole interchange CMF = 0.374 (MO, no fatals) Edara (2015) ramp terminals CMF = 0.322 (MO, no fatals) Similar results in national study that will be released shortly Conclusion: Results indicate that DDIs are SAFER than multilane roundabouts as ramp terminals!
CONTACT INFORMATION Questions??? Gilbert Chlewicki, PE Advanced Transportation Solutions gchlewicki@ats-american.com www.ats-american.com www.divergingdiamond.com 301.395.9971 37