If east is positive and a car is moving east and accelerating west, what is happening to its speed? velocity?

-- Its speed is decreasing.  If the situation keeps up long enough, the speed
will decrease to zero, and then begin to increase again.

-- The magnitude of the velocity is decreasing, but its direction remains pointing
to the East.  If the situation keeps up long enough, the magnitude of the velocity
will decrease to zero, and then immediately begin to increase again with the
direction pointing to the West.