Warning horns—Audibility versus environmental impact

The original standards for the warning horns used in the UK were based on a combination of listening trials and available technology. Underlying this work was the need to provide people working on the track with an adequate warning of an approaching train. Recent changes to the way track workers are protected mean that this primary function of warning horns is no longer required. Train drivers currently use the horns either when they see someone on or near the track who may be in danger from the approaching train, or when a ‘Whistle Board’ is used to provide a warning for anyone using a foot crossing. At the same time as the changes to the warning procedures there have been a growing number of complaints about the noise produced by warning horns. Starting with a simulation of the original tests this paper examines the characteristics of an audible warning that would meet current requirements for audibility at some foot crossings while at the same time minimising environmental impact.