Judgement of the National Green Tribunal in the matter of Dileep B. Nevatia Vs State of Maharashtra Others dated 11/10/2013. NGT has directed the Ministry of Road Transport & Highways to notify the standards for sirens and multi-toned horns used by different vehicles either under Government duty or otherwise within a period of 3 months hence. Based upon the standards to be prescribed by the Ministry of Road Transport and Highways, Government of India, the State of Maharashtra and the Transport Commissioner, Government of Maharashtra, Respondent Nos. 1 and 3 respectively will take adequate step to notify the standards for sirens and multi-toned horns for different zone, within a period of one month from the date of the notification.

Original Source: http://www.greentribunal.gov.in/judgment/202_2013(WZ)(MApp)_11oct2013_final_order.pdf