The value of freight moved between the U.S. and its North American Free Trade Agreement partners increased for the 11th straight month during September, according to new Transportation Department figures, but it's the smallest gain since April.

The 3.6% overall rise from the same time a year ago came as three of the five major transportation modes carried more freight by value between the U.S., Canada and Mexico.

The value of commodities moving by vessel increased 28.6%, pipeline by 9.1%, and truck by 2.9%. Rail decreased by 3.3% and air decreased by 3.4%. The large percentage increase in the value of goods moving by vessel was due in part to an increase in the unit value and a 6.1% increase in the volume of mineral fuels traded, according to the report.

Trucks carried 64.3% of U.S.-NAFTA freight and continued to be the most utilized mode for moving goods to and from both U.S.-NAFTA partners. Trucks accounted for $31 billion of the $50.2 billion of imports, or 61.8%, and $29.7 billion of the $44.2 billion of exports, or 67.2%.

Rail remained the second largest mode by value, moving 14.9% of all U.S.-NAFTA freight, followed by vessel, 6.7%; pipeline, 5.2%; and air, 3.9%.

The surface transportation modes of truck, rail and pipeline carried 84.4% of the total value of U.S.-NAFTA freight flows.

U.S.-Canada Freight Moves Up by 5%

Comparing September 2016 to September 2017, the value of U.S.-Canada freight flows increased by 5% to $48.5 billion as the value of freight on four major modes increased from a year earlier.

The value of freight carried on vessel increased by 52.4% due in part to an increase in the unit value and a 23.9% increase in the volume of mineral fuels traded, according to the report. Pipeline increased by 11.1%, truck by 3.1%, and rail by 2.4%. Air decreased by 5%.

Trucks carried 58.6% of the value of the freight to and from Canada. Rail carried 16% followed by pipeline, 9.5%; air, 4.6%; and vessel, 4.3%. The surface transportation modes of truck, rail and pipeline carried 84.1% of the value of total U.S.-Canada freight flows.

In September 2017, the top commodity category transported between the U.S. and Canada was vehicles and parts, of which $5.2 billion, or 57.1%, moved by truck and $3.6 billion, or 40.3% by rail.

U.S.-Mexico Freight Rises More than 2%

The value of U.S.-Mexico freight flows increased by 2.1% in September compared to a year earlier, totaling $45.9 billion as the value of freight on two major modes increased from a year earlier.

The value of commodities moved by vessel increased by 19.4%, and truck by 2.8%. Air decreased by 0.6%, rail by 9.6%, and pipeline by 15.9% due primarily to decreases in the volumes of mineral fuels exported.

Trucks carried 70.4% of the value of freight to and from Mexico. Rail carried 13.6% followed by vessel, 9.2%; air, 3.0%; and pipeline, 0.6%. The surface transportation modes of truck, rail and pipeline carried 84.6% of the value of total U.S.-Mexico freight flows.

The top commodity category transported between the U.S. and Mexico in September 2017 was electrical machinery, of which $8.1 billion, or 92%, moved by truck and $0.5 billion, or 5.5%, moved by air.