CO2, Speedchecks and Smoking.

How often do I hear of the advice to drive in third gear to avoid exceeding the 30mph speed limit? I heard this again in the Archers, Radio 4. Naturally the carbon emissions are likely to be nearly double in 3rd than in 6th gear. Clearly most cars will not go slow enough in top gear. There is an argument to increase the 30 limit in towns to 40mph say, between the hours of midnight and 7am. This will allow a more efficient use of our roads and a reduction in CO2 emissions.
22 February.
I attempted to check my speedometer using a speed check numeric beacon parked on the pavement near Heatherwood roundabout. I turned off the air conditioning and windscreen wipers since I have discovered that spurious reflections from these can confuse the electronics in the radar.
The beacon worked fine when I was the only vehicle on the road but often read about 10% high if there was approaching traffic. This seems to me to go against the laws of Physics. Could anyone suggest a reason for this?
I heard on the radio today that the European Politicians have decided that the smoking ban in public places will not apply to the European Parliament building. So often, it seem, the Great and the Good pass laws which are imposed upon us poor sheep and our livelihood can be taken away from us if we transgress by one iota. We blindly tow the line when we know that by doing so will serve no purpose. Many of our Leaders however, consider themselves far too important to be burdened with such triviality!