'HERE SEEMS TO BE MORE OPINION THAN By A. A. Towns*,
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SCIENCE IN ROADSIDE SMOKE CHECKS
AT what point does the emission of diesel smoke become sufficiently serious to be liable to result in prosecution? At what point can a Ministry of Transport vehicle examiner impose an order requiring it to be reduced, within a specified period? How are these points to he defined? None of these questions was satisfactorily answered by the method of operation of the spot check at which t was invited to
be present last week. .
It took place on A2 at. a point near Strood. A long hill with a gradient around 1 in 25 was chosen, and the observation point Was about two-thirds of the way up: A team of official observers was drawn from the vehicle examiners of the South-Eastern Licensing Authority, with a certifying officer in charge.
The opportunity Was taken to eirry out an inspection of such items as brake and steering on vehicles that were stopped in the now-familiar manner.
The surprising feature. of the whole operation was its haphazard nature. By this 1 certainly do not imply any personal criticism of the Ministry of T_ransp staff who carried it out, They are, course, knowledgeable and experien1 in matters of commercial vehicle ci struction and were undoubtedly trying carry out the spirit of the exercise_ However, technical knowledge d not include superhuman powers judgment and ultimately the decision to whether a particular amount of strn .was excessive or not depended entii on the opinion of the observers,ba on what they could see. No instrurne for measuring the intensity of smoke w used throughout the two hours dur which the check was in operation. Th could be no guarantee that the standa applied at Strood would he exactly same as those used, elsewhere in country..
The method of operation was as folio Three of the observers on the "offsic of the road watched lorries climbing hill. There was a very gradual curve vehicles came into View when about • yards away and were watched until t had passed the check point. One obser was equipped with binoculars and r details of the make, type of body, whet .loaded or not and, if picked out a: "smoker,' the registration number.
Aleague recorded these details on a rinted forth which had columns headed slight," " medium" and " excessive" rider a general smoke emission heading. these were inserted .7 Lick" marks when le degree • of smoking; if any, was !cided upon. The third observer atched each vehicle as it approached the leek point and, if it was seen to he noking to the appropriate degree, gave ie word to the police to stop it.
The driver was then asked if he would tree to tests being carried out. So far ; could be seen, none objected. although ost appeared to be a little bewildered y the procedure. Some were asked to :v the engine up to full speed to cheek ir smoke emission under no-load con.tions, although this procedure did not, . itself, apparently play any part in .qermining whether the vehicle was assified as a smoker."
In fairness it must be said that many, .obably the majority, of the vehicles opped undoubtedly emitted enough noke to be a nuisance to following :hides, although this was sometimes more because of smell than obstruction to vision. I did not see more than one or two that could actually be regarded as even slightly dangerous to other road users. Some vehicles which were seen to smoke were not stopped because of traffic congestion or because the static testing facilities were fully occupied, but these were noted and would receive written notification of any further action to be taken.
With most vehicles the degree of smoke emission depended on the load applied to the engine and its speed, so that the speed of other traffic had some influence on the likelihood of a vehicle being marked down as a smoker. In one or two cases at least this probably accounted for vehicles which passed the control point without being noted as smoking by the official team but which were seen by others present to smoke noticeably on the slightly steeper gradient encountered farther up the hill.
Estimating the amount of smoke emitted visually had obvious limitations and there was no doubt that in border
line cases it could be influenced by the presence or otherwise of sunlight and whether the smoke was viewed against the light or not. The eolour of the background and the position of the exhaust could also affect this.
In one particular case, an old but outwardly well-maintained fairground lorry, the exhaust was discharged upwards behind the cab. Some exhaust smoke was visible againstthe sky as it approached, but it became evident when the smoke could be viewed against a background of trees, as the vehicle came nearer, that it was blue in colour and, in my opinion, very slight in density. This strongly suggested slight burning of lubricating oil of the kind often observed before a diesel engine is thoroughly warmed-up. The vehicle was stopped, although no static tests appear to have been carried out before it was allowed to resume its journey.
Despite an obvious desire on the part of the Ministry of Transport officials concerned to operate the tests as fairly as possible, the lack of precise standards for deciding the borderline cases rnade much of the procedure appear to be haphazard. Some 12 vehicles were stopped and a further 12 noted as smoking among the 200-odd diesels which were observed. I have the impression that a good lawyer could demolish most of the evidence if any were to be prosecuted, although this was understood tc be unlikely at this stage.