From the Journal of Commerce:

Over-the-road shippers worried about peak-season capacity this fall need to focus on the front of the truck, not the back. There will be trailers available ready to receive freight, and enough trucks to pull them. What may be missing is the key ingredient in truck capacity: the driver.

The escalating driver shortage has become the leading check on over-the-road truck capacity, and if freight demand continues to stay above 2013 levels, the shortage is likely to lead to sharp increases in transportation pricing, as carriers pull out all stops to recruit and keep drivers.

More at the Journal of Commerce