Safety Performance of the Median Cable Barrier Deerfoot Trail, Calgary, Alberta UPDATE
Authors: Robyn V. McGregor, M.Sc., P.Eng. Senior Transportation Engineer & Principal Consultant EBA Engineering Consultants Ltd., Calgary Masood Hassan, Ph.D., P.Eng. Senior Transportation Engineer EBA Engineering Consultants Ltd., Edmonton Olivier Lahey, P.Eng. Operations Engineer, Calgary District Alberta Transportation
Scope of Presentation This presentation covers: Summary of design aspects Safety experience with the median cable barrier for the 22-month period May 2007 to March 2009.
Two Messages Forgiving Roadsides are a good idea. The introduction of median barriers is more complicated than we might think, so we should do our homework.
Project Overview Deerfoot Trail (Highway 2), Calgary: Six Lane Divided Freeway Rural X-Section Project length: 10.8 km High Traffic Volume 6:1 or flatter median side slopes 2.4 m (8 ft) paved inside shoulder
Pictorial Overview 16 m Median North of 16 th Avenue NE 30 m Median, South of Country Hills Boulevard
Defining the Specifications High tension (post-tensioned), 3- or 4-cable median barrier; posts in sockets in concrete foundations Main system: NCHRP Report 350 Test Level 4 (TL-4), tested for 8000 kg single-unit truck End-anchors: TL-4, or TL-3 (tested for 2000 kg pickup) FHWA-approved for 6:1 median side slopes Maximum deflection = 2.4 m (8 ft) Maximum post spacing = 6.1 m (20 ft) Competitive bidding
TL-4 Cable Barriers Available in 2006 Approved TL-4 Cable Barriers Available (Spring 2006) Barrier Characteristic Brifen (4 cables) Gibraltar (3 cables) Trinity (3 cables) Date of FHWA Approval- Letter Mar 27, 2005 Sept 9, 2005 Nov 17, 2005 Test: Post Spacing, m 3.2 6.1 6.1 Test: Maximum Deflection, m 2.4 2. 4 2.3 Cable Height from Ground, m Top Cable Middle Cable 4th Cable Bottom Cable 0.930 0.780 0.630 0.480 0.991 0.762-0.508 0.965 0.749-0.533 FHWA- Approved End Treatment TL-3, TL-4 TL-3 TL-3 Rule for Placement on 6:1 Median Side Slope Do not place on the median side slope between 0.3 m and 2.4 m (1 ft and 8 ft) from ditch bottom.
Design Aspect: Lateral Placement Median ditch deemed unsuitable for cable barrier Placed 4.0 m from painted shoulder line in the northbound direction
Existing Barriers & Hazards For hazards with existing barriers: cable barrier system runs past existing beam barriers with 0.9 m minimum separation between the two barrier systems For hazards without barriers: cable barrier runs past the hazards with 2.5 m minimum separation
Longitudinal Placement of the Barrier
Separation from Existing Barriers (0.9 m minimum)
Separation from Hazards (2.5 m minimum)
Anchor End Terminal (NCHRP 350 TL-3 Approved)
Anchor End Terminal Non-Crashworthy
Collision Experience May 2007 to March 2009 99 hits 3 penetrations (but did not result in cross over collisions) Mostly PDO Very few minor Injury NO FATALITIES Repaired and back in service within a few hours
Northbound Passenger Vehicle (3 Posts)
Northbound Pickup Truck
Same Northbound Pickup Truck (31 posts)
New Developments Dramatic reductions in crossover collisions have made median cable barriers popular worldwide Five current suppliers: Brifen, Gibraltar, Nucor, Safence, Trinity AASHTO Technology Implementation Group has an active cable barrier sub-group http://tig.transportation.org/?siteid=57&pageid=2197 MASH-08
Future Installations in Alberta 8 km of median cable barrier planned for Alberta Highway 2 in Airdrie in 2010 Alberta Transportation is considering the installation of 124 km of median cable barrier on Alberta Highway 2 between Airdrie and Red Deer and near Leduc New design challenges presented
Concluding Comments Forgiving Roadsides are a good idea. The introduction of median cable barriers is more complicated than we might think, so we must do our homework.
Our homework. Designers should research and utilize the latest approved products and related guidelines by FHWA and AASHTO. Talk to the vendors and other jurisdictions. Conduct Road Safety Audits. Monitor the performance. Apply what you learn to anything you put in the median and roadside.
rmcgregor@eba.ca