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My 2 pence (caution, only for european road conditions):
1) Road debris is not an issue over here. On the autobahn, nothing survives more than 30 seconds before being shredded and cast aside :-) If there is something substantial lying on the road, police will be quite quick to clear it. And if you want to anticipate every possibility, you need your whole stopping distance as a safety cushion anyway. This will only work at 3 a.m. though...
2) In my optinion, the old 3 second rule is for half-asleep drivers in mediocre 60s cars (you may call that worst case). A modern car can stop inside 40 m (app. 120 ft.) or better on dry road from 100 km/h. Given the fact that a trailer rig will stop AT BEST as fast as a normal car (in any weather condition), we only speak about reaction time which must be buffered by the distance between truck and car. For an alert driver, one second should be quite luxurious, which translates to 22 metres at 80 km/h.
3) Give the truck drivers some pause... neither are they idiots, nor do they drive as clueless as many car drivers do. The overwhelming majority of truck drivers I have encountered do not mind someone using their wind gap (though not many of them know they even save fuel when someone tailgates them as he fills up their energy-consuming low pressure drag pocket) and drive very anticipatory to conserve their fuel.
The only time I had to hit the brakes hard when trailing a truck was when that guy slammed the brakes because I was trailing him. It was a good adrenalin rush, but far from a close call. And that was one case in a whole year of rather intensive drafting.
Most hairy situations I encounter arise from people not looking where they want to drive but just driving there...
To provide some numbers:
usual trip to work yields around 4,0-5,1 l/100km depending on how much I can use trucks for drafting (scangauge numbers). The extreme numbers are more due to head- or tailwind and other weather and traffic conditions, I would say between 4,3 and 4,8 l/100km is the usual range. So 10% is a good estimate of the savings. Maybe less for a car with low cd value, my van has one near that of castle Neuschwanstein.
so long,
tinduck
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