Monday, June 28, 2021
ONRSR is reminding rail transport operators about a range of risks, causes and controls associated with short warning times at level crossings caused by wheel-rail interface issues.
Level crossings are designed to provide the appropriate warning of an approaching train or trains to motorists, cyclists and pedestrians. This “warning time” is defined as the time between the level crossing activating and when the train first enters the crossing. A short warning time (SWT) is when the time between crossing activation and the first train entering the crossing is less than the minimum design warning time.
These incidents can result in collisions and derailments that can ultimately cause serious injuries and even fatalities. One of several factors that can cause a SWT incident are wheel-rail interface issues and ONRSR’s investigations have shown there are a number of 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.
Why does wheel or rail contamination cause SWTs?
Electrical train detection equipment (track circuits) work by sending an electrical current through the steel of the railway tracks creating an electrical circuit. The electrical circuit is monitored by electrical equipment (a track relay). When a train passes over the railway tracks, the wheels of the train shorts the electrical circuit. In railway terminology, this ‘short-circuiting’ is known as ‘shunting’ or ‘dropping the track’. If there is wheel or rail contamination, the presence of the train wheels may not shunt the track because the electrical current is not able travel from the rail to the wheels of the train. This poor electrical conductivity can then result in the track relay being unable to adequately detect the presence of the train.
What are common causes of poor electrical conductivity?
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 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.
The following controls are likely to eliminate the risk but this may not be reasonably practicable - see the ONRSR Guideline – Meaning of duty to ensure safety so far as is reasonably practicable SFAIRP for more information):
The engineering controls railways have employed can be categorised into the following:
Train Detection Systems
Two of the train detection systems can be employed to better detect the presence of trains to reduce the likelihood of SWTs due to wheel-rail interface issues:
Some of the administrative and organisational controls railways can employ to mitigate the risks associated with short warning times at level crossings include:
Track maintenance controls:
This information is provided as guidance only.