ArcBest Corp., the parent of less-than-truckload (LTL) carrier ABF freight System Inc., said today that it will raise its tariff rates by 5.9 percent on or before April 16, the company's second general rate increase in less than a year.

Fort Smith, Ark.-based ArcBest gave no explanation in its statement for the move. Its last general rate increase, 4.9 percent, came last May.

Truck rates have been rising, in some cases dramatically, across LTL and the much larger truckload space. However, LTL carriers, operating in a concentrated market dominated by the top seven or so companies, have been raising their rates for several years. The more fragmented truckload category is just now following suit, though they are doing it in much larger increments that by mid-single-digit amounts.

The announcement comes as the ABF unit is negotiating a new collective bargaining agreement with the 8,600 workers who are members of the Teamsters union. Last week, leaders of both sides said they had tentatively reached an accord, details of which are unavailable. Union leaders will present the proposal to the rank-and-file next week.