the end time t 108 of the sustained braking demand 143 the ecu 22 then creates a modified driver demand mdd 147 which as before is the original driver demand signal 224 multiplied by the inverse of the over ride logical value 146 when the over ride value 146 changes the ecu 22 also applies smoothing to any required change in the modified driver demand 147 in the example of fig3 this smoothing results in a falling ramp 148 that lasts for a time u03b4t 105 starting at time t 105 after the initial change in the over ride value 146 from zero to one similarly a rising ramp 52 is applied that lasts for a time u03b4t 6 54 starting at time t 108 following the change in the over ride value 146 from one to zero the ramps each change the modified driver demand 147 at a constant rate with the rate of the falling ramp 148 being less than the rate of the rising ramp 52 the length in time 149 54 of the ramps 148 52 therefore depends on the magnitude of the required change in the modified driver demand 147 but will normally be between 0 1 and 1 0 s although in this example the driver demand threshold and braking demand threshold are shown as.