Wind tunnel technology

[lio007]

Wind tunnels became a talking point in the last couple of years with McLaren, Aston Martin and Red Bull investing in new facilities.

It's hard for me to figure out what is cutting edge technology in the wind tunnel sector. In what kind of aspects is a new wind tunnel better than an old one?

E.g. rolling roads
Does it make sense to use a 3-belt or is Single-belt used across all teams?

[Greg Locock]

The standard deviation of a round robin test on various wind tunnels around the world was ~0.01 for Cd, out of 0.30, and worse (in percentage terms) for lift at each axle.

So yes there is plenty of room for improvement.