Wire Rope Barriers in Victoria

 

By Nicholas Szwed    BEng(Civil), MEngSc, MIEAust, MITE,    VicRoads.  

 

 

Abstract

 

Wire rope barriers were introduced in Victoria during the 1990's. This paper presents a decade of experience in the use of wire rope barriers in Victoria. It reports on the findings of a literature search and a before-and-after crash study.

 

The conclusions are that wire rope barriers are generally the safest types of barrier and they are very cost-effective. Wire rope barriers should be the preferred barrier types and the alternatives used only where it is not possible to use wire rope, such as where adequate deflection clearances cannot be obtained.

 

 

1       Introduction

 

Each year, in Victoria, about 145 people are killed in run-off-road crashes and over 3,000 are injured. The cost of this road trauma is about $400 million per year.

 

About 60% of run-off-road casualty crashes involve a collision with a roadside hazard. The following table shows the most frequently struck roadside hazards.

 


Figure 1 – Types of objects struck

 

The most frequently struck objects are trees and poles.

 

The preferred countermeasures for such crashes are to remove, relocate or modify the roadside hazard. If that cannot be achieved then the installation of barriers to protect motorists against a more severe crash should be considered.

 

 

 

 

 

There are basically four types of barriers in use in Victoria:

 

1        Flexible eg wire rope barriers

2        Semi-flexible eg steel beam guardrail

3        Rigid eg F-shape or New Jersey concrete barriers

4        Crash cushions

 

The steel beam guardrail and New Jersey have been in use for many years and have been used extensively in Victoria. In the past, guardrail has been the preferred barrier from a road trauma perspective because it is more flexible and forgiving in terms of damage to the motorist or vehicle. The concrete barriers have been used where there has not been enough width to use the semi-flexible alternative or for the protection of structures such as bridge piers or where a low maintenance treatment was required. The concrete barrier has also been considered to be more effective in constraining heavy vehicles than the steel beam guardrail.

 

2       Wire Rope Barrier

 

In the mid 1990’s VicRoads started to use wire rope barriers because of their excellent reputation overseas, particularly in the UK.

 

The following table shows the locations where VicRoads had installed significant lengths of wire rope barriers up until last year.

 

 

Road name

Location

Installation date

 

Frankston Fwy

1. Dandenong – Frankston Rd overpass

2. Skye Rd to 420m south

June 1998

June 1996

Geelong Rd

(Princes Fwy West)

Point Cook Rd to Maltby Bypass

September 1996 to January 1997

Eastern Fwy

Hoddle St to Bulleen Rd

May 2001

Hume Fwy

1. Sharp and Taylors Rd to Ennis Rd (left of southbound carriageway)
2. From 70.5km to Ennis Rd (left & right of northbound carriageway)

1998

1998

 

Table 1 - Locations of wire rope barriers

 

2.1        Literature

 

A literature search carried out for VicRoads by MUARC concluded that wire rope barrier is the most appropriate barrier for maximising road safety benefits for road users.

 

MUARC also found that in Victoria, there are about two fatalities per year as a result of vehicles crashing into barriers (steel or concrete). MUARC could not find any evidence in the literature of any road users being killed in a crash with wire rope barrier anywhere in the world.

 

2.2        Before and After Study

 

A before-and-after crash study has been carried out at the locations in the above table to determine the effect that the wire rope barrier has had on crashes. The following table presents a summary of the crash analysis.

 

 

 

 

 

Run-off-road crashes

 

 

 

 

 

 

 

Before

After

 

 

Location

Length

(km)

Years

Casualty Crashes

Years

Casualty Crashes

 

 

 

 

 

F

SI

OI

Total

 

F

SI

OI

Total

 

 

Eastern Fwy

8

10

2

16

20

38

1

0

2

0

2

 

 

Geelong Rd

5

5

3

7

6

16

3

0

0

0

0

 

 

Frankston Fwy (1)

0.42

5

1

2

1

4

5

0

0

0

0

 

 

Frankston Fwy (2)

 

5

1

1

1

3

3

0

1

0

1

 

 

Hume Fwy (1)

1.25

5

2

2

2

6

3

0

0

0

0

 

 

Hume Fwy (2)

2

5

0

5

3

8

3

0

0

0

0

 

 

Total ~

17

35

9

33

33

75

18

0

3

0

3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 2 – Before-and-after crash summary

 

There were 75 run-off-road casualty crashes in the cumulative before period of 35 years, an average of 2.14 casualty crashes per year.

 

In the cumulative after period of 18 years, there were only 3 run-off-road casualty crashes, an average of 0.17 casualty crashes per year.

 

This represents a reduction of 92% in run-off-road crashes.

 

If the crashes had continued at the same rate as before the wire rope was installed, there would have been 39 casualty crashes including 5 fatal crashes. This means that the wire rope barriers have saved 36 casualty crashes including 5 fatal crashes, a saving of about $5m to the community.

 

These results support the contention that because wire rope barriers are flexible and forgiving they cause less road trauma than semi-flexible and, in particular, rigid barriers.

 

2.3        Cost Comparison

 

Accurate installation and maintenance costing information was difficult to obtain because records were not always kept in a form that could be extracted and compared accurately. However, based on the limited available data the minimum indicative installation costs of the three linear barrier systems are as follows.

 

Wire rope barrier:         $130+ per metre

W-beam steel barrier:   $120+ per metre

Concrete barrier:          $150+ per metre.

 

In terms of maintenance, wire rope barrier appears to have a significantly lower cost than steel barrier and concrete is considered to be generally maintenance free.

 

3       Conclusions

 

The primary purpose of crash barriers is to reduce the severity of road crashes. Both overseas and local experience indicates that wire rope barriers have the best performance in this regard.  In Victoria wire rope barrier has been found to reduce run-off-road crashes by 92%. The installation and maintenance costs of wire rope barriers are competitive with the alternatives. However, if the impact on road trauma is considered, then wire rope barrier is the most cost-effective system and should be considered in the first instance. The alternatives should only be considered where it is not possible to use wire rope.