The Act Commentary on sections Section 7: Investigations
29.Section 7 makes provision as to the railway accidents or incidents that the RAIB is to investigate.
	Subsection (1)(a) requires the RAIB to investigate serious accidents. Subsection (1)(b) provides the RAIB with discretion as to whether or not to investigate non- serious accidents or any incident. Subsection 1(c) provides that the RAIB is also to investigate non-serious accidents or incidents, if it is required to by regulations made by the Secretary of State.
	Subsection (2), however, provides for the Chief Inspector of Rail Accidents to exercise discretion when considering whether or not to investigate a serious accident on a tramway. Although accidents and incidents affecting tramways fall within the remit of the RAIB, the effect of section 7(2) gives the Chief Inspector discretion as to whether or not to investigate tramway accidents. This is because tramways run in various types of alignment, on street, alongside a highway, or off street. The investigation of an accident affecting a road-running part of a tramway would fall normally to the police to investigate whilst an accident affecting an off-street running part of a tramway would normally be investigated by the RAIB.
	Subsections (3) and (5) when taken together make clear that the RAIB is to try to work out the cause of the accident, without apportioning blame or liability. Although it will not consider blame or liability, the RAIB will publish a report setting out the cause even if blame or liability may be inferred as a result. These provisions are equivalent to those existing for the AAIB in regulation 4 of the Civil Aviation (Investigation of Air Accidents and Incidents) Regulations 1996, and for the MAIB in regulation 4 of the Merchant Shipping (Accident Investigation and Reporting) Regulations 1999.