Affect of highway barriers? Affect of side drafting large vehicles?

[freebeard]

As soon as the wall I am hugging curves to the left, or the truck I am pacing obscures an on-ramp or, worse, someone making a left turn onto the road, I get very nervous.

[jime57]

1. I used to see pictures of race cars at Indy and they pulled away from the wall a car width once on the straight. A commentator said that the drag was higher right against the wall. Gotta believe those guys know what they are doing.

2. My experience both with my own race car and on the road convinces me that there is a slight drag reduction on the rear corner of "good" vehicles, like trucks. Unfortunately, the trucks are usually going too fast, so any small gain is lost to the overall aero drag, not to mention the on/off throttle required to maintain position. IMHO, it doesn't work for fuel economy.

[jamesqf]

The walls certainly can help (or hurt) if there are strong winds. There are a couple of stretches I drive where there are frequent strong winds and sound walls. On one, it's a headwind from the right quarter, so driving on the right side of the right lane gives a noticable increase in fuel economy. On the other, it's a tailwind from behind or the left quarter, which the wall to the right intensifies, so that on a really windy day I can almost coast at 65 mph.