asked the Minister of Transport what research his Department is undertaking regarding the possibility of altering the construction and angle of the exhaust pipes of diesel lorries in view of the skid hazards caused by exhaust fumes settling on road surfaces; and what proposals he has to make.

Studies made by the Road Research Laboratory do not suggest that deposits from diesel exhaust fumes constitute a skid hazard of any importance on modern road surfaces.

While thanking my hon. Friend for that reply— [HON. MEMBERS: "Why?"]—may I ask him if he is aware of the findings of the United States Transport Department, whose researches have resulted in a substantial alteration in the construction and positioning of diesel exhausts on vehicles? Will he not reconsider his Answer in the light of the American experience, which has been successful?

The Road Research Laboratory has considered this matter. We do not consider, in the light of its views, that special research to deal with this problem— which is not considered to be a significant one—would be justified at present.

Can my hon. Friend say whether the inquiries made by the Road Research Laboratory show that these fumes represent a health hazard? Would any advantage be achieved by having exhaust pipes, especially of public vehicles and heavy lorries, discharging from higher up?

No, Sir. This would not be advantageous at ail. Most of the constituents of the exhaust are heavier than air. Together with soot and gas and particles of carbon they would fall on passers-by and bicyclists and enter the rooms of houses by the roadside—which would be worse than the present arrangement, whereby at least exhaust pipes expel fumes at ground level.