Came across an article detailing BMW's new facility. They boast:
The BMW Group’s new Aerodynamic Test Centre is the world’s most modern facility of its kind throughout the entire automotive industry.
- world’s largest rolling road in a wind tunnel
Most of the article seems to focus on high speed & handling issues related to aero though, like the ability to study aero during overtaking manouvers, or over bumps, or in curves.
The best part of the article is the photo gallery of scale & full size models in the tunnel: