The Freight Transportation Services Index rose 1.9 percent in May from its April level, the largest monthly increase since January, according to the U.S. Department of Transportation's Bureau of Transportation Statistics.

Since an increase in January that was the largest in two years, the freight index failed to advance over the three months ending in April, before rising in May to return to its January level. At 111.4 in May, the freight TSI was up 3.2 percent since its recent low of 108.0 in September 2007 but down 1.5 percent from its peak of 113.1 reached in November 2005.

The 2.8 percent increase in the freight index since December marked the fifth consecutive year the index increased in the first five months.

The freight TSI measures the month-to-month changes in the output of services provided by the for-hire freight transportation industries. The index consists of data from for-hire trucking, rail, inland waterways, pipelines and air freight.

The May 2008 freight TSI level was 2.1 percent above the May 2007 level of 109.2. The freight index remains below its May 2005 level of 111.7.

Despite declines from May 2005 level, the freight index has increased 8.7 percent in five years and 10.9 percent in 10 years.

The TSI is a seasonally adjusted index that measures changes from the monthly average of the base year of 2000. It includes historic data from 1990 to the present.