For safety towards pedestrians and other road-vehicles, sound alert systems, like horns, have been in use since development of Automobiles. On the same line but with special purpose of preventing a Driver to sleep in a running vehicle, a Driver Monitoring System [DMS] is recently developed. For Electric Vehicles which are very quiet during starting and driving till 20 km/hr, Acoustic Vehicle Alert System (AVAS) is deployed in Europe and likely to be implemented in India soon.
For all these Alert Devices, there are Standard Regulations across the world: ECE R-28 for Horns and ECE R-138 for AVAS. They, however, define only lower and upper dBA limits of the sound radiated by them. For DMS, no such regulation exists till today. With this, there has been a long time debate on what an optimal dBA level should be there, for all road-users as well as for vehicle- users inside the cabin. It should be adequate, on one side, from detectability point of view and, on the other side, it should not cause human- discomfort & noise pollution to environment.
This paper discusses these two aspects in details and recommends solutions over the conflicting demands from these Sound Alert Devices based on experimental findings over a no. of passenger and commercial vehicles inside an anechoic chamber and on the test-track. This is supported by Jury Evaluation, too, with rankings given for their preference for both alertness of a passing vehicle and pleasantness of the alerting message.
Limitation of the sound as the only medium for alerting the road users is brought to notice for dense Traffic conditions in a highly populated country like India. Here, the sound of AVAS or horns could be weak in comparison with very high background noise levels in certain zones. Different design solutions are given to overcome this. At the same time, design guidelines are discussed for minimization of environmental noise pollution and for the right sound quality of all horns, AVAS and DMS assuring the best comfort inside cabin of the vehicles in running conditions.
