INGENIEUR
Figure 11: Clearance zone was not provided
behind the guardrail
grade axle bolts had been utilised. The apparent
difference between the original and the failed
bolts illustrates an improper fastener selection
for the axle, one of the most critical structures
in a vehicle. Substandard components should be
prohibited from usage as its properties are not
in accordance with standard requirements due
to inappropriate material composition and heat
treatment.
Figure12: A deflecting guardrail should divert the
run-off vehicle back onto the road
3. Crash Barrier Failure
Accidents involving crash barrier failure have
been regularly encountered by MIROS. In road
accidents involving shoulder crash barriers or
guardrails, the common failure is the failure of the
guardrail to contain an errant vehicle and deflect
it back to its normal course. The failure usually
is due to non-compliance with the guardrail
installation standard. As an example, in the bus
crash mentioned earlier where a bus ran through a
guardrail, slid down a slope and overturned, it was
found that the dynamic deflection or clearance
zone was not provided behind the guardrail (Figure
11). The clearance zone is defined as an area from
the guardrail to the beginning of a hazard, in this
case the embankment slope. As illustrated in
Figure 12, a deflecting guardrail should divert the
run-off vehicle back onto the road, hence allowing
the driver to regain control of the vehicle.
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VOL 76
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JUNE 2013
In addition, improper end-treatment of the
guardrail posed a hazard to the traveling vehicle.
Based on cases investigated by MIROS, the
protruding end of the guardrail causes errant
vehicles to be penetrated by the stiff panel of
the guardrail, injuring the occupant as shown in
Figure 13. The protruding end of guardrails are
usually found in the gap section between median
guardrails as shown in Figure 13. Likewise, in
another case, improper end treatment of a bridge
barrier caused the bridge railing to penetrate the
bus’ passengers’ compartment and fatally injured
10 occupants (Figure 14). The investigation of
the site revealed that the bridge barrier was not
properly installed according to the standards. The
end treatment of the bridge should have been
installed in alignment with the concrete barriers to
avoid the railing from protruding.