Specific guidance for taking safety decisions on the Railtrack-controlled infrastructure is set out by Railtrack in its Railway Safety Case , which is accepted by Her Majesty 's Railway Inspectorate ( HMRI ) . In summary , where risks lie in the `` as low as reasonably practicable '' ( ALARP ) region , decisions on whether to implement further safety measures are guided by balancing safety benefits ( i.e . reductions in risk ) against the cost of undertaking those measures .