Someone must have thought that it would fly apart at 90 rpm and harpoon a motorist on 58 a hundred yards away.
Any problems due to imbalance will increase with the square of the free spinning rotational speed but the rotational speed was hardly 3X the design rpm. It's not like a disk wind turbine needs a whole lot of dynamic balancing. It could probably safely spin at 300 rpm.
Second, the odds of it actually hitting a vehicle would be nearly zero even if it did come apart.
The disruption to traffic was a much greater cost than any risk presented by the wind turbine
Bret Cahill