Frisco FD/EMS, Plano FD/EMS, and DPS troopers are working a rollover accident on northbound Sam Rayburn Tollway near Preston Road. Multiple vehicles involved with one overturned. At least two patients with serious to critical injuries. Frisco Battalion 1 has command and Truck 2, Engine 2, and Medic 8 are all working along with Plano Engine 7, Medic 7, and Truck 8. Expect heavy delays in this area.