INGAL Ezy-Guard 4, Product Manual

Page: 7 / 34

Roadside Safety Barrier
7
Release 07/22b
Figure 4: Vehicle Trajectory
6.0 Performance
Ezy-Guard 4 provides protection from roadside hazards
located close to the edge of the travelled way. The
sectional strength of the 4 Z-post reduces lateral
deflection whilst providing controlled containment and
redirection.
Crash testing guidelines provide a set of requirements
that is “worst practical conditions” in order to demonstrate
the barriers impact performance. When the combined
effects of vehicle mass, impact speed and angle of
impact are considered, the testing criteria represents the
extremes of impact conditions to be expected in real-
world situations.
6.1 Deflection
The transverse deflection of a barrier during a crash is
dependent upon the mass, speed, and impact angle of
the errant vehicle.
Since crash testing typically represents the extremes
of these parameters, a review of the proposed barrier
location can be undertaken to assess the following;
•
Maximum attainable impact angle;
•
Design speed; and
• Design vehicle.
Figure 4 illustrates the vehicle trajectory when turned
towards the barrier. The maximum attainable angle, Ø is
limited by the speed of the vehicle and the lateral offset,
x to the barrier.
The maximum attainable angle for various speeds and
offsets is shown in Figure 6 and is derived using a point
mass model and assumes maximum steering and a
coefficient of friction of 0.7 (dry pavement).
If the deflection needs to be reduced due to the
proximity of a road side hazard, this can be achieved by
reducing the post spacing. Refer to Tables 1a and 1b for
deflections with reduced post spacing. The reduced post
spacing should be initiated 8m upstream and returned
to standard spacing 8m downstream of the hazard.
If designing for a containment level of TL4, designers
should also consider the potential roll of the larger vehicle.
Guidance on the calculation of roll allowance is detailed
in the Austroads Guide to Road Design - Section 6.3.16.
Refer Table 1b for NCHRP-350 TL4 deflection.
6.2 Slopes
The maximum cross fall for an installation of Ezy-Guard is
10H:1V (10%).
6.3 Batter Hinge Proximity
Installations of safety barriers in close proximity to a
batter hinge point should be considered within the
requirements of the road controlling authority Extended
Design Domain.
Ezy-Guard Smart has been successfully crash tested to
MASH TL3 with posts installed on the rounding point
of a 2H:1V batter. The batter was comprised of AASHTO
M147-65 Standard Soil.
Suitability of the ground conditions and/or erosion of the
batter should be considered by the installation designer
prior to installation of a safety barrier near a batter slope.
It is recommended the barrier be installed with the
maximum offset to hinge point possible. For NCHRP-350
TL4 containment, the offset to back of post should be
1.3m.
As the proximity of the batter slope may reduce the soil
support to the post, the designer should also consider the
use of an increased post embedment, refer section 7.5.2.
vehicle
barrier
x
vehicle
barrier
x
vehicle path
Figure 5: Ezy-Guard Smart on curves