When following a semi I make sure I can see there rear view mirrors that way you know they can see you. Getting any closer than that is not worth a couple of mpgs. Unless your driving a hummer.

 

A Hummer might double its mileage in a draft, as almost all the gas consumption goes into overcoming air resistance with its massively unaerodynamic shape.

 

I think of it much like pushing a brick through peanut butter.

On drafting and following distance:
I draft frequently on my commutes, but only if there are few other vehicles present. If there are many other vehicles on the road there are that many more reasons for rapid deceleration and while there is a chance of a collision you are also garounteed to destroy kinetic energy which defeats the point of your hybrid, and be counter productive. So you're being unsafe unnecesarily.

 

What is drafting?

 

Following closely behind another, similarly sized or (preferably) larger, object to reduce wind resistance/drag and thereby reduce the amount of energy expenditure required to go the same speed as the object one is following.

I say "object" because bicylists do it all the time (think Tour de France), not just NASCAR racers, professional long haul truckers, and some fuel economy-seeking citizens.

I prefer to maintain adequate following distance when driving, but when cycling it can come in real handy... except it's a little messy if you're mountain biking off-road, because the one drafting is eating all the dirt/dust kicked up by the lead bike. Not that different from drafting on the roadways, actually.

More: Drafting (Wikipedia)

 

Breathing highly toxic diesel exhaust and risking decapitation from rear ending a semi?

Uhmmmm . . .
Let me think . . .
Ummmmm . . . No Thanks!

My MPG is just fine without drafting.

 

Hell yeah it does! On a recent trip to Detroit (180 one-way miles) I averaged 45mpg while drafting a tour bus that had its cruise sitting on 78mph. I was able to follow him for around 110 miles on the I80/90 Toll Road with no slowing down. I reset Trip B when I started drafting and when he exited I was showing 45mpg.

No, that's not a typo. 78mph.. 45mpg... 110 miles.

 

How close did you have to follow for these results?

 

I personally don't get closer than five car lengths to anything, semi or not.

The recirculate button with the windows rolled up should protect you from particulate matter, five car lengths should provide enough room for evasive action if necessary, and a good attention span should allay those fears.

And yes, I agree your stellar mileage numbers don't need any help from drafting. I can only imagine what consistent 60MPG tanks feel like.

 

I was easly 4-6 car lengths back... you can feel it. And you can see it on the instant MPG!

I don't think there's much too scary even 3-4 carlengths... think about it... a semi once the brake lights come on, barely even stops for a second or so.. and with an HCH you stop probably in 3x shorter length... so unless the semi hits a brick wall you're fine.

Of course I'm used to high performance road course driving, following behind a Corvette at 125mph at 2 car lengths and diving in under him in the corner