W-Beam Guardrail

Semi-Rigid Protection

Product Manual
Ref: PM 003/03
W-Beam Guardrail
Semi-Rigid Protection

Table of Contents
1.0 Introduction .................................................................................................................... 3
2.0 W-Beam Guardrail ........................................................................................................ 3
3.0 How W-Beam Guardrail Works ............................................................................... 4
4.0 Design Considerations ................................................................................................. 6
4.1 End Terminals ..................................................................................................................................6

4.1.1 Trailing End Protection .........................................................................................................6

4.2 The Point-of-Need ...........................................................................................................................7

4.3 Recommended Minimum Length ..............................................................................................7

4.4 Double-Sided Configuration ........................................................................................................7

4.5 Site Grading Requirements .........................................................................................................8

4.5.1 Advance Grading .....................................................................................................................8

4.5.2 Adjacent Grading .....................................................................................................................8

4.5.3 Run-Out Grading ......................................................................................................................8

4.6 Kerbs ................................................................................................................................................ 11

4.7 Culverts ........................................................................................................................................... 11

4.8 Transition to Rigid Barrier ....................................................................................................... 11

4.9 Pedestrians & Cyclists ................................................................................................................ 11

4.10 Shy Line Offset ............................................................................................................................ 12

4.11 Flaring ........................................................................................................................................... 12

5.0 Curving ............................................................................................................................ 13

6.0 Summary ........................................................................................................................ 14

7.0 Designers Checklist .................................................................................................... 15

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W-Beam Guardrail
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1.0 Introduction 2.0 W-Beam Guardrail

Providing a forgiving roadside environment reduces W-beam guardrail is the world’s most widely
the consequences for vehicles leaving the safe, specified safety barrier system offering protection
travelled way. Hazards such as trees, utility poles, from hazards located adjacent to the travelled way.
culverts and embankments are often located W-beam guardrail provides designers an economical
adjacent to roadways and relocating them is often and dependable roadside solution.
impractical. In these instances, shielding with a
longitudinal safety barrier is the most appropriate W-beam guardrail comprises a rail element, known
solution. as w-beam, that is blocked out from specially-
engineered supporting posts. Adjacent rails are
Roadside safety barrier designs have developed over bolted together forming a splice connection and end
the years and are used to safely contain and re- terminals are placed at either end to anchor the
direct errant vehicle away from nearby hazards. system.
Safety barriers reduce the severity of run-off-the-
road crashes and have made a significant W-beam systems vary throughout Australia. Whilst
contribution to the safety of our region’s roads. the rail element design remains the same, the
design of the supporting posts and blocking pieces
Longitudinal barriers are typically classified into vary according to state road authority requirements.
three categories;
The w-beam systems adopted within Australia
 Flexible barriers: designed to move substantially incorporate the use of C-posts (Queensland, NSW,
during a vehicle impact. The energy of the S.A. & W.A.) or U-posts (Victoria and Tasmania).
impacting vehicle is absorbed by movement of
the barrier; W-beam guardrail using C-posts or U-posts is
regarded as a semi-rigid barrier. A semi-rigid barrier
 Semi-rigid barriers: designed for moderate provides a desirable outcome for both designer and
movement during a vehicle impact. The energy the vehicle occupants. The lateral displacement of
of the impacting vehicle is absorbed by the system, also known as deflection, is typically
movement of the barrier and deformation of the limited to 1m providing protection from nearby
barrier; and roadside hazards. The ability of w-beam guardrail to
absorb some of the crash energy reduces occupant
 Rigid barriers: designed for no movement risk and limits deformation of the impacting vehicle.
during a vehicle impact. The energy of the
impacting vehicle is absorbed by the
deformation of the vehicle.

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Semi-Rigid Protection

3.0 How W-Beam Guardrail Works

110mm
Safe vehicle containment and re-direction is
developed through a combination of the flexural
resistance of the rail and the bending resistance of
the supporting posts.
150mm C-Post
Upon impact, the posts absorb some of the crash
energy through post rotation in the surrounding soil
prior to separation from the rail as they fully yield.
The blocking pieces, positioned between the rail and
posts, minimise vehicle snagging and reduce the 76mm
potential for the vehicle to vault over the barrier by
maintaining rail height during the initial stages of
impact.
Once the rail separates from the posts, the rail forms
a re-directive ribbon, guiding the vehicle away from
178mm U-Post
the nearby hazard.

The sectional strength of the posts, spaced every 2m

or 2.5m (Victoria), combined with the flexural
strength of the rail, limits the deflection of the
system during impact. Figure 1: Post Profiles

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W-Beam Guardrail
Semi-Rigid Protection

Tasmania – 690mm
NSW & SA – 710mm
WA & Qld – 730mm

Ground Line

All States (except Qld) – 1800mm

Queensland – 1850mm

Figure 2: W-Beam Assembly Detail

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W-Beam Guardrail
Semi-Rigid Protection

4.0 Design Considerations It is a requirement that all w-beam guardrail systems

be appropriately anchored at the leading and trailing
4.1 End Terminals end of the installation. It is necessary that the
leading end of the system be anchored with a
End terminals are the specially designed end pieces crashworthy end terminal such as the SKT-SP or
located at the leading and trailing end of the w- FLEAT-SP.
beam guardrail system.
4.1.1 Trailing End Protection
End terminals are designed to anchor the w-beam
guardrail system and introduce the necessary tensile In some instances it is necessary to install a
and flexural strength required for safe vehicle crashworthy terminal on the trailing end. This occurs
containment and re-direction throughout the when the trailing end of a guardrail barrier is located
length-of-need section. within the clear zone of approaching traffic.

Some guardrail end terminals also provide the The clear zone is the horizontal width of space
additional feature of reducing the severity of an available for the safe use of an errant vehicle. This
impact near or at the end of the system. distance is dependent upon the posted speed and
road geometry. Guidelines for determining the clear
zone width are contained within state road authority
publications.

Clear Zone Width

for Vehicle 1

Crashworthy Terminals Required on Approach

and Trailing End when within Clear Zone of
Vehicles 1 & 2

Clear Zone Width

1 Travelled Path for Vehicle 2

Travelled Path 2

Clear Zone Width

for Vehicle 1 Clear Zone Width
for Vehicle 2

Figure 3: Assessment of Trailing End Protection safedirection.com.au 6

W-Beam Guardrail
Semi-Rigid Protection

4.2 The Point-of-Need Whilst the point-of-need location may vary between
terminal types, provided the terminal point-of-need
W-beam guardrail is designed to safely contain and and the site beginning-length-of-need are
re-direct errant vehicles away from roadside horizontally aligned, the road safety barrier system
hazards. The point-of-need is the location where the will provide the same re-directive capabilities,
barrier becomes re-directive. regardless of the terminal selected.

The point-of-need is typically dependent upon the 4.3 Recommended Minimum Length
terminal selected to anchor the w-beam system. For
terminals such as the SKT-SP and FLEAT-SP the The recommended minimum length of w-beam
point-of-need location is terminal post 3, a distance guardrail on high speed roads to effectively contain
of 3.81m downstream from the start of the system. and re-direct an errant vehicle is 30m between
terminals.
It is necessary that the point-of-need location is
appropriately aligned with the hazard that is being 4.4 Double-Sided Configuration
shielded. Figure 4 provides an example.
When installed in a central median, w-beam
guardrail can be installed with blocking pieces
mounted to either side of a single post.

Terminal
Point-of-Need

Hazard

Edge of Shoulder

Direction of Travel

a = Angle of Departure

Figure 4: Positioning of Terminal Point-of-Need to Adequately Shield a Roadside Hazard

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4.5 Site Grading Requirements 4.5.3 Run-Out Grading

Grading around the area of a road safety barrier is It is a requirement that all w-beam guardrail barriers
an important consideration. The site grading should be appropriately anchored with an end terminal.
be considered from three perspectives; advance When there exists an opportunity for an errant
grading, adjacent grading and run-out grading. vehicle to strike the end of the w-beam system,
consideration must be given to the area parallel to
Under crash test conditions, the surfaces and behind the system. When struck at or near the
immediately in front of and behind w-beam nose at an angle of 15° or greater, w-beam guardrail
guardrail barriers are reasonably flat and end terminals will yield, allowing a vehicle to
unobstructed. In the field, conditions vary from site continue into the area immediately behind and
to site and obstructions such as kerbs, services and beyond the terminal.
embankments are encountered.
AS/NZS 3845 nominates an area measuring 22.5m
4.5.1 Advance Grading long x 6.0m wide measured from the nose of the
terminal to be reasonably traversable and free from
It is recommended that the area in advance of the fixed object hazards. This may be difficult to address,
w-beam guardrail barrier be limited to a grading of particularly on existing roadways. This is recognised
10H:1V to ensure that the vehicle’s suspension is by AS/NZS 3845 which also states that ‘if a clear run-
neither extended nor compressed at the moment of out area is not possible, this area should at least be
impact. The selection of a tangential end terminal similar in character to adjacent unshielded roadside
such as the SKT-SP may reduce the requirement for areas’.
earthworks normally associated with the use of a
traditional parabolic flared terminal such as the When the desirable run-out area is not available or
MELT. when there is a high likelihood of a head-on impact
with the terminal, the use of an energy-absorbing
4.5.2 Adjacent Grading terminal such as the SKT-SP or FLEAT-SP should be
the preferred option over a non energy-absorbing
Adjacent grading refers to the surface on which the terminal such as the MELT.
w-beam guardrail is installed and the area
immediately behind. It is recommended that this The ability of energy-absorbing terminals to
area be relatively flat (10H:1V) so that the terrain dissipate energy during head-on impacts and bring
does not contribute to vehicle behaviour. The an errant vehicle travelling at high-speed to a
supporting posts of the w-beam guardrail barrier controlled stop over a short distance reduces the
should have 600mm of fill material behind them, opportunity for an errant vehicle to pass behind the
providing sufficient lateral support. system.

On existing roads with limited formation, positioning

posts on the hinge point may be the only option. It is
recommended that the post embedment depth be
increased to provide sufficient lateral support.
Guidelines for calculating the increased post
embedment are detailed in Figure 7.

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Semi-Rigid Protection

Edge of Batter
Variable Taper 600mm
1500mm Grading of 10H:1V

Edge of Shoulder

Direction of Travel

Figure 5: Recommended Advance Grading for W-Beam Guardrail with Tangential End Terminal

Shy Line Offset

(refer to Table 1)

600mm to
Hinge Point

Grading of 10H:1V Travelled Way

Figure 6: Recommended Adjacent Grading for W-Beam Guardrail

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Semi-Rigid Protection

Existing Roadway with Post

Installed at Hinge Point

Additional Embedment Depth

= 1000mm/α

Embankment
(α)H:1V

Standard Embedment Depth

Figure 7: Guidelines for Increasing Post Embedment Depth (Source: Qld Main Roads Drawing 1474)

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W-Beam Guardrail
Semi-Rigid Protection

4.6 Kerbs 4.9 Pedestrians and Cyclists

Placing kerbs in front of w-beam guardrail on high- Pedestrians or cyclists may require shielding by a
speed roads is not recommended. As an alternative, road safety barrier in situations where they are
a shallow gutter in front of the barrier or subsurface considered to be exposed to a higher than normal
grated drainage should be considered. risk of being struck by an errant vehicle. Where a
pedestrian/cyclist facility either exists or is proposed
On lower speed roads that often require a kerb, it is for an existing site that has a run-off-road crash
recommended that the location of the barrier be history, an assessment of pedestrian, cyclist and
200mm from the face of kerb. This reduces nuisance bystander exposure should be undertaken so that
impacts and minimises the potential for vehicle crash reductions for alternative treatments can be
launching. considered.

4.7 Culverts Cyclists and pedestrians may require a barrier to

prevent them inadvertently running onto a traffic
When culverts are encountered the use of a post lane from an adjacent shared path (e.g. footpath on
mounted on a base plate may be considered. Where a bridge with high numbers of young
a base plate post cannot be accommodated, a span pedestrians/cyclists). In cases where there is no
of up to 6m is generally permitted without a need to protect path users from errant vehicles, or
supporting post provided the rail is nested (i.e. errant vehicles from roadside hazards, a pedestrian
double layer) throughout this location. fence of a suitable height for cyclists should be
adequate.
When providing a barrier system over a culvert, the
area behind the safety barrier system should be Where there is a need to provide a road safety
sufficient to accommodate the expected dynamic barrier between a path and road traffic it is
deflection of the barrier. important that the rear of the road safety barrier is
not a hazard for pedestrians and cyclists. Where
4.8 Transition to Rigid Barrier sufficient clearance cannot be provided, cyclists are
protected from ‘snagging’ on posts by the provision
Since the stiffness properties vary between a semi- of suitably designed rub rails.
rigid and rigid barrier, a specially designed transition
is required when connecting w-beam guardrail to a Designers should ensure that any modification or
rigid barrier such as concrete. attachments to the barrier would not be detrimental
to its performance under vehicle impact or result in
A transition gradually increases the lateral stiffness components being hazardous to motorists or path
of the w-beam guardrail barrier and reduces the users in the event of a crash with the barrier (e.g.
potential for vehicle pocketing at the connection horizontal rails spearing vehicles).
with the rigid barrier. Transition designs are
contained within state road authority specifications.

Typically transition designs incorporate the use of

thrie-beam (triple corrugation rail) and a reduction
in post spacing.

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W-Beam Guardrail
Semi-Rigid Protection

4.10 Shy Line Offset Flaring the safety barrier system provides the
following benefits;
Drivers tend to reduce speed or laterally move their
vehicles away from a road safety barrier if it is within  The end terminals can be positioned further
close proximity to the edge of the travelled way. from the travelled path reducing the potential
for a head-on impact;
The distance from the edge of the travelled way
beyond which a safety barrier will not be perceived  The shy line effects where a hazard is close to
as an immediate hazard by the typical driver is the travelled path is minimised; and
known as the shy line offset. Recommendations for
the shy line offset are contained in Table 1.  Flaring provides a gradual transition to a major
hazard close to the roadway (such as a bridge
Table 1: Shy Line Offset parapet or railing).
Design Speed (km/h) Shy Line Offset (m)
The maximum flare rates that should be used on an
50 1.1
approach to a road safety barrier are shown in Table
60 1.4 2. Following the guidelines of Table 2 ensures that
70 1.7 the flare does not significantly increase the
80 2.0 opportunity for high-angle impacts with the barrier.
90 2.2
Table 2: Flare Rate
100 2.4
Flare Rate Flare Rate
110 2.8 Design Speed
(within Shy (outside Shy
(km/h)
Source: Austroads Design Guide Line Offset) Line Offset)
50 13:1 7:1
4.11 Flaring
60 16:1 8:1
Motorists are less likely to perceive roadside barriers 70 18:1 10:1
to be a hazard if the barrier is introduced gradually
80 21:1 11:1
to the roadside environment through the use of a
‘flare’. Consequently, some end treatments for w- 90 24:1 12:1
beam guardrail barriers such as the FLEAT-SP are 100 26:1 14:1
designed to be flared away from the approaching
110 30:1 15:1
traffic. The flare rate is the ratio of the length of the
flared part of the barrier (measured parallel to the Source: Austroads Design Guide
road) to the barrier offset.
The flare rate for end terminals such as the FLEAT-SP
vary from those contained in Table 2. Please refer to
specific Product Guides for allowable flare rates for
end terminals.

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5.0 Curving
H
W-beam guardrail performs well on the outside of
curves, even those of relatively small radius, as the
C
concave shape (in plan view) supports the
development of tension in the w-beam rail. Ø
Radius
In the field, straight sections of w-beam can be used
to form a radius of 45m or greater. When a radius of
less than 45m is required, the w-beam rails are
required to be factory curved. For ordering
purposes, the orientation of curvature and radius is
required by the manufacturer.
Convex Concave
Table 3 details the chord length (C), height offset
(H), and angle (Ø) for various curved rails.

Figure 8: Curving Detail

Table 3: W-Beam Guardrail Curving
4m W-Beam Guardrail 5m W-Beam Guardrail (Victoria)
Radius (m) Ø (Degrees) C (mm) H (mm) Ø (Degrees) C (mm) H (mm)
2.4 95.5 3553 786 119.4 4144 1189
3.0 76.4 3710 642 95.5 4441 983
4.0 57.3 3835 490 71.6 4681 756
5.0 45.8 3894 395 57.3 4794 612
6.0 38.2 3926 330 47.8 4857 513
7.0 32.7 3946 284 40.9 4894 442
8.0 28.7 3958 249 35.8 4919 387
9.0 25.5 3967 221 31.8 4936 345
10 22.9 3973 199 28.7 4948 311
12 19.1 3982 166 23.9 4964 259
14 16.4 3986 143 20.5 4973 223
16 14.7 3990 125 17.9 4980 195
20 11.5 3993 100 14.3 4987 156
24 9.6 3995 83 11.9 4991 130
28 8.2 3997 71 10.2 4993 112
32 7.2 3997 62 8.9 4995 98
35 6.6 3998 57 8.2 4996 89
40 5.7 3998 50 7.2 4997 78
45 5.1 3999 44 6.4 4997 69
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6.0 Summary  The blocking pieces, positioned between the rail

and posts, minimise vehicle snagging and reduce
 W-beam guardrail is the world’s most widely the potential for the vehicle to vault over the
specified safety barrier system. barrier by maintaining rail height during the
initial stages of impact.
 The semi-rigid feature of w-beam guardrail
provides a desirable outcome for both designer  Steel components are hot dip galvanised
and the vehicle occupants. The lateral providing a durable solution.
displacement of the system is typically limited to
1m providing protection from nearby roadside  W-beam guardrail performs well on the outside
hazards. The ability of the barrier to absorb of curves, even those of relatively small radius,
some of the crash energy reduces occupant risk as the concave shape (in plan view) supports the
and the deformation of the impacting vehicle. development of tension in the w-beam rail.

 The semi-rigid feature of w-beam guardrail  W-beam guardrail can be installed using posts
limits damage during impact, reducing on base plates when passing culverts.
maintenance costs.
 The high visibility of w-beam guardrail creates
 The Australian post and block design has driver confidence.
demonstrated excellent in-service performance
over many years.

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7.0 Designers Checklist

 Calculate the beginning length-of-need required to shield the roadside hazard.

 Calculate the clear zone width and determine whether a crashworthy end terminal such as the SKT-SP or
FLEAT-SP is required on the trailing end. Refer to example shown in Figure 3.

 Ensure the end terminal point-of-need is appropriately aligned with the site beginning length-of-need.
Refer to example shown in Figure 4.

 Ensure appropriate grading is provided in advance and adjacent to the w-beam guardrail barrier. Refer
to examples shown in Figures 5 and 6.

 If the barrier is to be installed on an existing road with limited formation, assess the post embedment
depth following the guidelines of Figure 7.

 Consider locating the barrier outside the shy line offset in accordance with Table 1.

 Consider providing a flare throughout the system in accordance with Table 2.

 If the guardrail system follows a curved alignment, determine whether the straight rails can be used or if
factory curving will be required.

 Ensure the guideline for minimum length between terminals is observed.

 On high-speed roads, provide a shallow gutter or subsurface grated drainage as an alternative to a kerb.

 Undertake a risk assessment if pedestrians and/or cyclists will be accessing the area behind the barrier.

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Above & Beyond Concepts Pty Ltd

36 Sandringham Avenue
Thornton NSW 2322 Australia
Ph: (02) 4028 6155
E: sales@abovebeyondconcepts.com.au
abovebeyondconcepts.com.au
ABN 96 102 683 054

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