Shares in Swift Transportation, the largest truckload carrier in North America, were down 14% Friday after management warned it was going to have to invest more to address a driver shortage.

The New Jersey-based firm now says it's going to have to spend more on wages and training to hold onto and attract ore drivers.

...We were constrained in the truckload and (central refrigerated systems)  segments by the challenging driver market. Our driver turnover and unseated truck count were higher than anticipated. Therefore, we sold more trucks in the second quarter to offset the impact of idle equipment, which drove additional gains on sale of equipment this period. After assessing the current and expected environment, we believe the best investment we can make at this time, for all of our stakeholders, is in our drivers. Our goal is to clear the path for our drivers by helping them overcome challenges, eliminate wait times and take home more money.

It now sees "cost headwinds" going into the second half of the year.

The American Trucking Association has warned the country is short 30,000 drivers, and that the gap could climb to 200,000 in the next decade.