Martin Marietta Aggregates is a leading producer of construction aggregates in the United States. These include crushed stone, sand and gravel that are used to build roads, sidewalks and foundations.
There is a scarcity of limestone and hard rock in the United States. In 1994, 7% of the aggregates in the US were shipped by rail and 93% by truck. By 2006, trucking of aggregates dropped to 73%, while rail increased to 16% and 11% were shipped by water. In 2006, the cost per ton-mile was 15-35 cents for trucking, 6-11 cents for rail, and 0.4 to 1.2 cents for ships. Martin Marietta operates 15 limestone mines. Two of the major sites for producing aggregates are Nova Scotia and Freeport, Bahamas.