Instead of using a lead car to slow things down during yellow flags, the system relies on dashboard displays that tell racers to stay under a given speed limit; they face penalties if they go over. The technology is only being used in practice sessions this weekend, but the FIA is working with teams to determine just when VSC is viable for honest-to-goodness races.
That may take some time. While VSC is tentatively a success, some drivers are complaining that it's too difficult. They spend a lot of time staring at their dashboards rather than the road ahead, and they have to manage speed very carefully if they want to keep up when race organizers give the all-clear. Even so, the dash-based limit might be worth the hassles if it prevents one collision from leading to another.
