The physics, based on the Havok physics engine but almost entirely gutted and rewritten, allow for an extra dimension of interactivity in both single player and online environments. Character death can now be handled by ragdoll physics, and many physically simulated objects can exist in a map without notable performance hits. Source also provides sophisticated vehicle physics including torque, power, gears, tire material, suspension and mode. Multiple players can be in the same vehicle, but this feature has yet to be used.