As you can see Alan starts from a free-hand simple sketch that already has the right proportions, perspective, line quality and composition on the page. The wheels are very well done following the perspective.
What really is strong in this illustration is the control of its Focal Point (front wheel/hood/ground) with the light effect which is driving our attention to it first before admiring the rest of the illustration. Reading from left to right.
The balance between the light and shadow is perfect and the color treatment, too.