Improving speed limits for a safe and efficient service in bad weather
Although the need for speed restrictions in response to adverse weather is recognised, especially since RAIB’s report into the August 2020 Carmont crash, blanket speed restrictions (BSRs) can cause knock-on safety risks across the network. Industry needed a tool to ensure restrictions are proportionate.
Network Rail revised operational responses to adverse rainfall following the Carmont crash, including extending the use of BSRs. These were intended as an emergency measure and lacked detailed system-level data.
The North West and Central region of Network Rail asked RSSB to investigate and produce a solution.
RSSB developed a decision support tool to minimise the overall system risk during adverse weather.
Severe rainfall can cause earthwork failures that lead to derailment hazards. The risk of derailment is reduced by slowing down a train, but this also introduces other risks across the network.
PRIMA informs decisions on the application of speed restrictions, enabling the overall risk to be reduced as low as is reasonably practicable. This is achieved with three components:
- local vulnerability models that calculate the probability of earthwork failures
- local risk models that calculate train accident risk
- knock-on risk models that calculate whole system risk and disbenefits on implementing a speed restriction.
PRIMA supports Network Rail, other infrastructure managers, and train and freight operators to balance three parameters during adverse weather events: service levels to passengers, legal requirements for reducing safety risk to be as low as is reasonably practicable, and economic costs to rail.
PRIMA provides a key input to pre-determine the best speed restrictions during severe rainfall, so that response plans can be created for operational teams to quickly implement during periods of adverse weather.
This approach will enable rail organisations to respond more precisely and effectively to adverse weather, which will improve the passenger experience during these events.