easy way to create a realistic shadow.
1) clone the trailer layer so now you have 2 of them....
2) CTRL click the layer thumbnail so you select the entire selection.
3) While the selection is active make a solid fill with Black on top of the cloned layer.
4) Move the black layer behind the original trailer layer so you cannot see it.
5) Use the scale tool (edit, transform, scale) and set the object centerpoint to the bottom handle of the scale box. Drag the middle handle of the scale selection down until you start to squish the cloned black layer.
6) Use the skew/perspective tools to move the shadow from where the light is coming from, this will make it look like the shadow is really being cause by a light source.
7) Use the Gaussian Blur tool to give the shadow layer a nice soft feel to it, eliminating the hard edge.
8) Use the layer opacity to tone down the shadow layer.
all done.