The value of freight moved between the U.S. and its neighbors Canada and Mexico fell in August, totaling $92.4 billion, as all modes of transportation carried less value of freight than a year earlier.

A new U.S. Transportation Department report says the 8.1% decline from the same time in 2014 came as there were large decreases in the value of commodities moved by pipeline and vessel due to the reduced prices for mineral fuel.

In August compared to a year earlier, the value of commodities moving by truck decreased by 1.8%, while rail dropped by 8.4%.

A decline in the value of freight shipments does not necessarily mean there was a lower volume of freight transported, notes the department.

Trucks carried 63.6% of U.S.-North American Free Trade Agreement freight and was the most heavily utilized mode for moving goods to and from both U.S.-NAFTA partners. Trucks accounted for $29.7 billion of the $49.8 billion of imports, or 59.6% and $29.1 billion of the $42.7 billion of exports, or 68.3%.

Rail remained the second largest mode by value, moving 15.5% of all U.S.-NAFTA freight.

U.S.-Canada Freight Falls Even More

The value of U.S.-Canada freight totaled $48 billion in August 2015, down 13.6% from August 2014, as all modes of transportation carried less value of U.S.-Canada freight than a year earlier, due to lower mineral fuel prices. Mineral fuels are a large share of freight carried by pipeline and vessel, which were down 35.1% and 40.2%, respectively, year-over-year.

In August, the top commodity category for all modes transported between the U.S. and Canada was vehicles and parts, of which $5.5 billion, or 61.1%, moved by truck.

Trucks carried 58.1% of the $48 billion of freight to and from Canada, followed by rail at 15.8%.

U.S.-Mexico Sees More Truck Freight

The value of U.S.-Mexico freight totaled $44.5 billion in August 2015, down 1.4% from a year ago, but two out of five transportation modes, rail and truck, carried more U.S.-Mexico freight by value.

The top commodity category for all modes transported between the U.S. and Mexico in August was electrical machinery, of which $8.2 billion, or 92.3%, moved by truck.

Year-over-year, the value of U.S.-Mexico rail freight rose 3.2%, the largest percentage increase of any mode. Freight carried by truck increased by 1.5%.

Trucks carried 69.6% of the $44.5 billion of freight to and from Mexico, followed by rail at 15.1%.