46 SECTIONAL ADDRESSES 



' In respect of the " normal running test " : motor cycles, 

 heavy motor cars and motor tractors. 



* In respect of the " racing engine test " : motor cycles. 



' After two years the normal limits shall prevail. 



(3) 'As it is obvious that finality has not been reached in the art of 

 quietening mechanically propelled vehicles, the Minister should 

 reserve the right to amend in the future the above noise limits in 

 the light of further developments. 



(4) ' The Minister should by regulation make it an offence to cause or 

 permit the engine of a stationary vehicle to be run at excessive 

 speeds.' 



With regard to cars, both sf the ordinary and sports types, there can 

 be little doubt that conformity with the suggested limits is either already 

 attained or readily can be. The difficulties are doubtless greater in the 

 case of motor cycles and commercial vehicles, where it may be that an 

 acceptable degree of quietness is only attainable by a sacrifice of power 

 and an increased cost. It was felt, however, that given time the problem 

 was not insoluble, and a tolerance period of two years was accordingly 

 suggested to meet the situation. 



Polar diagrams which were obtained by exploring the sound distribu- 

 tion round a vehicle, indicate that ordinary cars and commercial vehicles 

 owe their loudest noise to their engines, while in the case of motor cycles 

 and certain sports cars, the loudest noise is in the direction of the exhaust 

 pipe. Extreme examples of the latter occur, and it was to meet these that 

 the racing engine test was introduced, as such cases may not reveal 

 themselves in the lateral noise measurements associated with the normal 

 running test. 



As regards the racing engine test, the engine speeds proposed are 

 those at which the maximum power is developed, and though the speeds 

 are high, they are not abnormally so. Still higher engine speeds may 

 produce a considerable increase in loudness — as much as 10 phons — and 

 the Committee felt that such misuse of a vehicle, for example in a quiet 

 street, would be best met by a regulation on the lines of recommendation 

 No. 4. 



(iii) Tests on ' used ' motor vehicles. — Having thus dealt with vehicles 

 fresh from the manufacturers, the Committee passed on to ' used ' or 

 ' old ' vehicles, and in their third report published a few months ago they 

 deal with this matter. Experience suggests that the noise from used 

 vehicles will normally be higher than from newly manufactured ones, 

 whether by reason of development in design, or as the result of normal 

 wear and tear, or unsatisfactory maintenance. The ultimate object of the 

 investigation on used vehicles was to study the feasibility of a common noise 

 limit for all classes of vehicles on the roads to-day, irrespective of their age 

 or circumstances of use. 



Accordingly a series of tests, on the lines of those in the earlier reports, 

 were undertaken on some 40 representative vehicles, including motor 

 cycles, motor cars and commercial vehicles, of various ages up to 13 years. 

 These tests were supplemented by random observations on some 600 



