A drive system includes a vehicle propulsion drive having a speed change gear box which drives tracks through a pair of planetary gears and a steering drive having a pair of variable hydrostatic drives. The hydrostatic drives engage a neutral shaft which superimposes rotation on the planetary gears to provide steering control for the tracks. The neutral shaft is separable into two segments. A differental reversing gear may be employed to selectively couple the neutral shaft segments. When the vehicle travels at high speed, the neutral shaft segments are coupled for unitary rotation. At low vehicle speeds, the propulsion drive is blocked and the neutral shaft segments are uncoupled so that both propulsion and steering are provided through the hydrostatic drives. For combined steering control and regulation of slow travel speeds as a function of the requirements of specific operating equipment carried by the vehicle, a control apparatus operates as a function of electrical signals for regulating travel speed and provides, through a linkage, adjustment of the hydrostatic unit controls and, in addition, superimposes upon the adjustment, modification required for steering the vehicle.