Why does one year of data need three years of context?
A single year of casualty data, particularly for smaller counts, will always fluctuate more than the network’s underlying safety actually does. That’s why every figure isn’t presented in isolation but is shown alongside the longer pre-pandemic average and the baseline figures.
Statistical significance testing is planned for a future update, to help flag which year-on-year movements in an area’s figures are likely to reflect a genuine change rather than ordinary fluctuation. Agilysis’ companion in-depth article, Measuring risk before it becomes harm, sets out that distinction in more detail.
What about authorities going through reorganisation?
Several highway authorities are well into Local Government Reorganisation, with some having new unitary boundaries proposed but not yet confirmed by government. Agilysis has deliberately built the current version on 2025 boundaries, the most recent confirmed geography, rather than estimating ahead of a decision that hasn’t been made yet.
A future update is planned once boundaries are confirmed, so that newly formed unitary authorities can see what their combined area SPIs already look like under the same baseline, rather than starting their reporting from zero on day one.