1. HIGH TENSION CABLE BARRIER IN THE MEDIAN OF A FREEWAY IN ALBERTA, CANADA: A CASE STUDY OF TWO SUCCESSFUL PROJECTS
TRB First International Roadside Safety Conference,
June 2017, San Francisco, California
Paul Steel, Masood Hassan & Gerard Kennedy - Tetra Tech Canada Bill Kenny - Alberta Transportation

2. PURPOSE & OUTLINE OF PRESENTATION
The purpose is to highlight interesting features of, and experience with, two successful high tension cable barrier (HTCB) projects in Alberta, Canada, that would be of interest to road safety professionals around the world.
Outline of presentation
Description of the two projects
Important design considerations
Safety effectiveness
Benefit-Cost analysis
Innovative construction techniques
Operation and maintenance experience
Concluding comments

3. HIGH TENSION CABLE BARRIERS
Pre-stretched, post-tensioned; 3- or 4-cable galvanized steel cables; 1,000ft lengths joined by turnbuckles
Proprietary systems (posts, terminals, foundations, post spacing, test deflection, etc.)
Acceptance by US Federal Highway Administration (FHWA) based on independent tests at various Test Levels.
Guidelines by FHWA and American Association of State Highway & Transportation Officials (AASHTO)

4. LOCATION OF THE TWO HTCB PROJECTS IN ALBERTA, CANADA

5. SUMMARY CHARACTERISTICS OF THE TWO ALBERTA HTCB PROECTS
ITEM
DEERFOOT TRAIL, WITHIN CITY OF CALGARY
HIGHWAY 2, CALGARY NORTHWARD
Cross section
6-lane divided
4- to 6-lane divided
Median type
Depressed median
Median width
16m to 31m
9m to 18m
Median side slopes
6:1
4:1 to 6:1
Cable barrier project length
11 highway-km
11 HTCB-km
122 highway-km
133 HTCB-km
(11km on both sides)
Traffic volume (AADT)
154,000
29,000 to 34,000
Speed limit
100 – 110 km/hr
110 km/hr
Year of HTCB constr’n
2007
2010
No. of cables
3 cables
4 cables

6. SALIENT DESIGN ELEMENTS OF THE TWO ALBERTA HTCB PROJECTS
DOT’s Design Bulletin for HTCB did not exist at the time
Consulted FHWA and AASHTO and US State-DOT officials
At least two FHWA-accepted HTCB systems must be eligible
Max. test deflection = 2.4m (8ft); Max. post spacing = 6.1m (20ft)
Cast-in-place concrete or driven steel foundations for posts and terminals acceptable (For Highway 2, precast concrete terminal foundations were allowed, with consequent movement problems)
Supplier’s design for terminal foundations to be confirmed or modified by an Alberta-certified geotechnical engineer on the basis of subsoil data

7. SALIENT DESIGN ELEMENTS OF THE TWO ALBERTA HTCB PROECTS (Cont’d)
Placement in the Median
FHWA guidelines applied
Placing near the shoulder preferred, provided the distance to the painted shoulder line, and to un- protected hazards in the median, exceeds the maximum specified (test) deflection.
If this condition cannot be met, the HTCB should be installed in the ditch or on both sides of the median.
Deerfoot Trail: all 11km placed near the shoulder
Highway 2: 55km near the shoulder; 56km in ditch centre; 11km on both sides.

8. SAFETY EFFECTIVENESS: DEERFOOT TRAIL
Median-related collision statistics for the before-HTCB period to 2006 (five years) were compared to the 32-month (May 2007 to December 2009) after-HTCB period.
The proportion of median related fatal collisions dropped from 4.4% to 0% (From 2007 to May 2017 there has been no median related fatal collision on Deerfoot Trail).
The proportion of median related injury collisions dropped from 21.1% to 11.8%.

9. SAFETY EFFECTIVENESS: HIGHWAY 2
Median related collision statistics for 63 months before-HTCB were compared to the 18-month after-HTCB period.
The proportion of median related fatal collisions dropped from 2.1% to 0.5%.
The proportion of median related injury collisions dropped from 34.5% to 10.0%

10. BENEFIT-COST ANALYSIS
ITEM
DEERFOOT TRAIL
HiIGHWAY 2
Highway & HTCB length
11 highway-km
(11 HTCB-km)
122 highway-km
(133 HTCB-km)
Traffic volume (AADT)
154,000
29,000 to 34,000
Year of HTCB Construction
2007
2010
No. of cables
3 cables
4 cables
Total Capital cost
$946,000
$7,500,000
Capital cost/HTCB-km
$92,000
$56,000
Maintenance cost/HTCB-km/year
$6,050
$3,790
20-year Net Present Value
$18,500,000
$53,100,000
Benefit-Cost Ratio
11.1
4.6
Payback period
<1 year
2 years
Note: amounts shown are in CDN $

11. INNOVATIVE CONSTRUCTION TECHNIQUES ON THE HIGHWAY 2 PROJECT
Vibratory Post Driver mounted on a mini- excavator to install the driven steel post sockets (Instead of the usual drop hammer technique)
Customized spool delivery truck to expedite production

12. INNOVATIVE CONSTRUCTION TECHNIQUES ON THE HIGHWAY 2 PROJECT (Cont’d.)
Special guide-post attachment to aid cable installation
Electric winch to tension the cable (Instead of the usual block and tackle arrangement)

13. INNOVATIVE CONSTRUCTION TECHNIQUE ON THE HIGHWAY 2 PROJECT (that didn’t quite work!)
Precast concrete foundations for end terminal anchors were allowed, resulting in terminal foundation movement problems

14. INNOVATIVE CONSTRUCTION TECHNIQUE ON THE HIGHWAY 2 PROJECT (Cont’d)
The innovations enabled the installation of 135km of HTCB in 45 days compared to an estimated 150 days with conventional installation methods, and more cheaply.
Of the 106 terminal foundations, 60% were driven steel, 35% precast concrete, and 5% cast-in-place concrete.
Majority of the precast concrete and driven steel terminal foundations exhibited some movement. Inspection indicated that this movement did not compromise the functionality of the HTCB. A few foundations required remedial action.
DOT now requires that terminal foundations must be cast-in- place concrete or driven steel; in the latter case they should be specified at a greater depth than the suppliers’ standard details.

15. OPERATION & MAINTENANCE EXPERIENCE
Deerfoot Trail 11km HTCB: 9-year ( ) Hit and Repair Record
Average no. of hits requiring replacement of parts = 0.3 hits per km per month
Average no. of parts replaced per hit
3.8 Posts (range 0–31)
4.8 hairpins (range 0–31)
5.1 lock plates
(range 0–31)

16. Maintenance and Operational Benefits of HTCB
Repair requires smaller crews; and is easier, quicker and cheaper (and with fewer snow problems) than more rigid barriers
Post replacement, cable splicing, re-tensioning are relatively simple
HTCB is functional in most cases following a hit, and can retain subsequent hits (except when terminal is down); no cable break experienced

17. Maintenance and Operational Issues and Challenges of HTCB
Greater need for maintenance-worker safety
High traffic roads require full traffic accommodation (Deerfoot Trail HTCB repairs are mostly done at night)
Some problems with mowing in the median, e.g. when trimming under the barrier in a narrow median, or when HTCB transitions from shoulder to ditch bottom requires mowing

18. Maintenance and Operational Issues and Challenges of HTCB (Cont’d)
Snow removal can be difficult in some snow-accumulation-prone areas where HTCB is near the shoulder (no longer possible to wing snow to ditch) leading to accumulation at the barrier which can accelerate snow drifting
Some activities (e.g. sign washing) now completed at night to limit exposure of workers and to reduce road user delays

19. CONCLUDING COMMENTS
Median HTCBs drastically reduce crossover fatalities and collision severity. And they are more cost-effective than conventional barriers.
HTCBs are easier and cheaper to maintain than conventional barriers.
The reaction of the public and emergency responders to the HTCB installations has been consistently positive.
Alberta experience indicates that, when planning and designing median HTCB installations, special attention to specific site conditions may be required, e.g. existing structures and conventional barriers in the median, or other local characteristics.

20. THE NEXT SLIDE WILL BE USED ONLY IF THERE IS A RELATED QUESTION FROM THE AUDIENCE.

21. SAFETY EFFECTIVENESS: HIGHWAY 2 Effect of HTCB placement, median width & median side slope during 18 months after HTCB installation
Factor
Collision Counts
Segment Properties
Median-Related Collision Rates (Collisions/100 Million veh-km)
All Collisions
Injury
Fatal
Highway Length (km)
Daily Traffic (Weighted AADT)
Barrier Location
Both Shoulders 94 8
12.87
33,500
42.09
3.58
0.00
Ditch
267 29 1
55.92
29,950
30.78
3.34
0.12
Shoulder
238 23 2
53.17
29,510
29.28
2.83
0.25
Total
599*
50* 3
121.96
Median Width
<= 9.0 m 80 10
17.43
28,620
30.96
3.87
> 9.0 m
478 47
104.53
29,980
29.45
2.90
0.18
558*
57*
Median Sideslope
4:1
136 13
15.21
33,260
52.28
4.96
0.38
5:1
313 30
73.16
27.66
2.64
0.09
6:1
150 16
33.59
30,060
28.87
3.06
0.19
59*