There is a complicated method. Though I would not guarantee its accuracy.
Fetch X,Y pos of the car.
Lets call them X1, Y1.
Accelerate the car in forward direction (without turning).
Stop the car.
Fetch X,Y pos again.
Call them X2, Y2.
Angle = tan-1 [ (Y2 - Y1)/(X2 - X1) ]
You can use a timer to get X2, Y2 while you are driving.