A.— MATHEMATICAL AND PHYSICAL SCIENCES 47 



vehicles in normal traffic on a variety of roads, some speed-restricted and 

 others unrestricted. 



The results were in general harmony with the previous conclusions, 

 and it appeared that a difference of about 5 phons between new and old 

 vehicles is an all-round representative figure which takes cognisance of 

 the many factors involved such as type, design, power, age and state of 

 repair. The evidence was, however, not sufficiently definite to indicate 

 that the noise was dependent on the age of the vehicles to any outstanding 

 degree. 



The measurements on normal traffic on the road were spread over a 

 range of approximately 70 to 105 phons, and from a study of the results, 

 it appeared that a general limit of 95 phons (B.S.) for the various classes 

 of vehicles was a reasonable figure, which would rule out the chief 

 offenders and would not be incompatible with the limit of 90 phons 

 proposed for the tests on newly-manufactured vehicles. If such a limit 

 were brought into force, the Committee was of opinion that the case of 

 vehicles already licensed on the roads could be met by a tolerance period 

 of two years. 



The tests indicated that greater progress had been made in the silencing 

 of sports cars than of motor cycles, many of which constitute at high speeds 

 the noisiest traffic on the road to-day. The Committee took the view that 

 the temporary figure of 95 phons suggested for the tolerance period in the 

 case of new motor cycles, should also suffice for motor cycles on the road 

 which are run at reasonable speeds. The Committee therefore submitted 

 to the Minister of Transport the following recommendations dealing 

 with used vehicles : — 



(i) ' When a vehicle is used on the public highway the loudness of the 

 noise emitted when measured at a point distant laterally 18 feet 

 from the mid-point of the vehicle, or 25 feet behind the open end 

 of the exhaust pipe shall not exceed 95 phons (B.S.). 



(2) ' A vehicle shall be regarded as complying with the above require- 

 ment if it can pass the following tests : ' — 



[Here follow the specifications for the ' normal running test ' 

 and the ' racing engine test ' as for new vehicles (pp. 59 and 60), 

 with the exception that ' 95 phons ' replaces ' 90 phons '.] 



(3) ' The noise limit of 95 phons (B.S.) for vehicles on the public 

 highway shall operate in the first case only in respect of vehicles 

 registered on or after the prescribed date, but shall come into 

 general application for vehicles of any age after two years have 

 elapsed from that date. 



(4) ' The Minister should reserve the right to amend in the future 

 the above noise limit in the light of further developments.' 



(iv) Summary of Ministry of Transport's reports.— To summarise the 

 three reports of the Ministry of Transport Committee, the position is 

 that for the first time in this country a comprehensive attack has been made 

 on the problem of road traffic noise. To this end, loudness measurements, 

 many thousands in number, have been conducted under widely differ- 

 ent working conditions, on the over-all noise of some 800 motor vehicles, 



