Abstract: An integrated jackknife control device for a tractor trailer assembly requires minimal if any modification to the existing fifth wheel coupler of the tractor trailer. The device comprises a computer controlled braking system including one or more pivot brakes acting directly on the trailer body, sensors which detect tractor trailer conditions indicative of incipient or full-fledged jackknifing and possibly other hazardous conditions such as collision or panic braking, and a proportional controller which causes one or more brake to apply a resistive force directly to the trailer which increases proportionally with a sensed degree of trailer jackknifing. The braking system preferably will automatically remain in a standby mode during backing maneuvers and will allow the operator to actuate the braking system manually and also to reset or return the braking system to a standby condition.