In Mexico City, NASCAR has placed tire packs around the track at the apex of several corners, even adding another one after the first practice session. While drivers may use as much pavement as they want in some areas, such as the exit of the final corner, NASCAR wants to avoid drivers cutting corners.
They've also painted yellow lines through the esses, and crossing that line will result in a stop-and-go penalty at a designated location around the track. But the addition of tire packs is a welcomed one for most drivers, who would rather focus on avoiding those than having to worry about the painted lines on the track.
