When the Ambulance Visibility website was in its infancy over ten years ago one of the first webpages to be written was concerned with the inadequacies of sirens as an effective warning for fire, police and ambulance vehicles. Stephen Solomon, David Green and De Lorenzo explained in their research that soundproofing in modern cars was becoming more efficient with each passing generation. Improved soundproofing coupled with louder radios and stereos, airconditioner noise and any wind or road noise inside the cabin was making it more difficult for drivers to hear an approaching emergency vehicle. In addition, the use of non-directional sirens made matters even worse, especially in cities with tall buildings and on roads with heavy traffic where the sound is reflected from many different directions. New ‘rumbler’ type sirens have been developed in an attempt to reduce these effects but with limited acceptance.
A US National Safety Council newsletter3 (April 1997, p1) reported on the results of a study by the American College of Orthopaedic Surgeons. The study demonstrated that the siren sounds of an ambulance proceeding at 100 kph barely precedes the ambulance, so that vehicles ahead of it cannot respond to its warning. The study showed that the distance for getting the attention of a motorist travelling at 100kph to be within 2 meters of the ambulance’s front bumper.
A new report published in the Accoustics Australia magazine last year tests and compares an Australian siren with a large number of international siren types including the Rumbler. The paper titled Accoustic Characteristics for Effective Ambulance Sirens and written by Howard, Maddern and Privopoulos from the University of Adelaide is a comprehensive examination highlighting the following points:
- At 90 degrees to the forward axis (intersections) the siren may be approx half as loud.
- “These results are consistent with Ref  that stating that the average siren attenuation, through closed-windows and typical masking noise, resulted in an effective distance of siren penetration of only 8-12 m at urban intersections, which is an insufficient distance to alert road users to safely clear the path.”
The most practical location for the siren is on the front bumper.
- Recommends a combination of current sirens + a low frequency rumbler.
- A different urgency tone should be used when crossing an intersection or responding through traffic lights etc.
- “The selection of an effective warning signal involves many competing factors that ultimately requires making compromises.”
Read the conference summary of the report – CLICK HERE
Read the report – CLICK HERE
I also came across a YouTube video recorded in Canberra that clearly demonstrates the lack of an audible warning inside a modern vehicle. The video shows a car travelling along a suburban road at about 80kph (50mph). Two AFP (police) vehicles approach from the rear (about 35 secs into the video) and the recording clearly shows how little warning time the sirens provide. The driver in the camera vehicle also lowers the volume of his stereo inside the car as he hears the police cars approaching. The second major issue is the increased likelihood of an unwanted event because the two police vehicles are travelling so close together. Drivers may see the first police vehicle but concentrating on the first they may not be aware of the second vehicle following closely behind.
More information on the Ambulance Visibility website under Sirens and research links in the AV Reference Library