Thursday, October 28, 2021

Safety Message – Rail bridges struck by road vehicles or vessels

Rail bridges, referred to as rail under bridges, are designed to safely carry rail over a roadway or waterway. However, bridges with low vertical clearance over a road or a waterway are susceptible to road vehicle or vessel collisions. Bridge strike incidents typically involve over-height road vehicles (such as trucks or lorries including loads) or vessels impacting against a bridge structure, bridge supports, piers and abutments. It may also involve over-width loads, colliding with the bridge supports or abutments.

These incidents can result in derailments and collisions that can ultimately cause serious injuries and even fatalities. ONRSR’s investigations have shown there are several mitigations that can minimise the risks. While not exhaustive, given the range of operational environments within the Australian rail industry, the following causes/contributing factors and controls should be noted.

Causes & contributing factors

1. Organisational factors e.g.

• suitable and available controls not put in place or not adequately maintained
• inadequate interface and communication agreements with third party road managers operators e.g. so that both the rail infrastructure manager and road manager know what risks and controls regarding the bridge interface they are responsible for
• taller truck heights and increase in volume of truck users
• lack of proper route planning by hauliers

2. Technological or equipment factors e.g.

• Administrative rather than higher level engineering controls put in place
• Lack of provision or signposting of alternative routes at low bridges
• Inadequate or poor warning signs on the approach to and at low bridges

3. Individual factors e.g.

• Drivers insufficient route knowledge or training
• Drivers not knowing the size of their vehicles
• Improper storage of equipment/loads on trucks
• Violation of vehicle warning signs

4. Environmental factors e.g.

• poor visibility of warning signs, speed boards
• weather conditions
• road gradients

Controls

While not an exhaustive list, ONRSR is aware of the following controls that are available and have been used in railways both in Australia and overseas. Rail Transport Operators (RTO) should note that there are safety and operational benefits and possible detriments associated with each control. Operators must consider a range of factors, including the likelihood of the hazard and the degree of harm to determine what controls are reasonably practicable to implement (see the ONRSR Guideline – Meaning of duty to ensure safety so far as is reasonably practicable SFAIRP for more information).

Elimination

The following controls are likely to eliminate the risk but this may not be reasonably practicable:

• Closing or diverting the road, closing or diverting the rail line.

(see the ONRSR Guideline – Meaning of duty to ensure safety so far as is reasonably practicable SFAIRP for more information)

Engineering

Some of the engineering controls that railways can employ to mitigate the risks associated with bridges strikes include the following:

Clearance controls:

• Vertical clearance controls include raising the level of the bridge soffit, lowering the road level, or both in accordance with the standards. As per AS5100, the minimum vertical clearance is 5.4m for bridges above freeways, main and arterial roads.
• Horizontal clearance ensures the distance from the roadway to the supports or piers of the bridge avoids a collision between the road vehicle and bridge piers or supports. Bridge standards mandate clearance requirements. For older bridges where moving piers or supports may not be possible, other controls, see below, can be used.

Load resistance controls:

• Lateral restraint controls can be put in place to prevent the superstructure being dislodged from its supports. Standards require bridge superstructures to have sufficient restraint to resist lateral and vertical forces from impact loads.
• Resistance controls for the underside of the bridge ensure its structural integrity is not compromised during a bridge strike. For example, this can include provision of lateral bracing and welding additional plates to steel beams, among others.
• Bridge support controls include provision of impact resistant piers, columns or abutments to prevent structural damage or collapse of the bridge. This includes designing piers or columns to ensure impact resistance, building redundancy into the bridge supports, and designing for impact loads in accordance with the specified standards.

Collision protection controls:

• Crash protection beams or crash beams, impact beams, bridge bumpers, or cushion systems are sacrificial structures designed to absorb the energy from vehicular impact forces on the superstructure.
• Collision protection barriers include deflection walls and crash walls and are sacrificial structures designed to absorb or divert impacts from vehicular impact forces on the bridge supports.

Administrative

Some of the administrative and organisational controls that railways can employ to mitigate the risks associated with bridges strikes include the following:

Signage and markings:

• Several types of passive signs and markings can be placed on the bridge or in front of the bridge and include e.g.:
  • Alternative stripes of black and white or red and white to make the bridge more conspicuous.
  • Warning signs that advise of the clearance height or low clearance, of the rail bridge ahead.
• Active signs which can provide variable messages regarding the bridge ahead or advise of where to divert should a vehicle be too large.

Height detection systems:

• Height detection gantries fitted with rubber paddles or metal chains that provide drivers a sensory warning (e.g. it will hit the road vehicle) alerting the driver they are approaching a low clearance bridge.
• Automated electronic detection systems placed in advance of the bridge to detect large vehicles and can provide specific warnings to road vehicle drivers (such as automated warnings) or alert the network controller who can then warn approaching trains.

Permit assessments, enforcement and response controls:

• Permit assessments and planning tools for oversized or heavy vehicle road users help determine the best routes for large vehicles to avoid travelling on roads with low clearance bridges. Permits are managed by the road authorities.
• Bridge strike response procedures and processes are actions that rail transport operators can take to mitigate potential safety impacts of bridge strike incidents. These include
  • notifying authorities and personnel including train drivers,
  • initial prompt actions such as stopping trains or putting in place speed restrictions,
  • assessing the bridge by competent inspector or engineer prior to resuming normal operations,
  • repairing any structural damage or track misalignment,
  • review of controls to prevent future strikes.

This information is provided as guidance only.