This study was commissioned by the Highways Agency to determine whether the noise generated by the firing of soil nails into embankments presents a safety hazard to road users. Fired soil nails provide a rapid means of stabilising shallow earthwork slips on the trunk road network thereby minimising traffic disruption to road users. However, the process of firing soil nails into the ground involves the generation of a sudden loud noise which may startle passing motorists and thereby present a safety hazard. TRL has carried out experiments in its driving simulator to determine drivers' reactions to an unannounced simulated nail firing noise and has deduced whether the sudden noise is likely to present a safety hazard to drivers. The results show that the noise levels generated at 7m from the firing device fitted with a silencer was well in excess of the 200 Pascal (140dB) sound pressure limit stipulated in the Health and Safety Executive Noise at Work Regulations. Noise levels measured before the silencer was fitted were, on average, 1.8dB greater for comparable measurements. The startle effect of the noise was such as to be capable of adversely affecting the driving behaviour of motorists, and thereby make the operation (without further silencing) hazardous for the site layout conditions investigated. (A)

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