This paper presents highlights of research conducted under Phase 2 of the Transportation Research Board's National Cooperative Freight Research Program 17 and reported in North American Marine Highways. The possibility of transporting greater volumes of chlorine and anhydrous ammonia via the marine highway system was investigated. Currently, there is no coast-to-coast (and only limited inland waterway) activity related to transportation of either chemical. The researchers identified major obstacles to development and expansion and corresponding potential courses of action. Geographical dispersion of producers and consumers works against greater waterborne volumes. Chlorine and anhydrous ammonia are characterized by mature, low-growth markets. Expansion of marine services will require significant capital costs and time to set up new terminals. There is great concern over the current condition of the system of locks and dams. Marine carriers face the same economic ramifications from risk of catastrophic accidents as rail carriers, necessitating the establishment of a new risk paradigm. The federal government could provide initial funds and expedite the permit process to allow new marine highway ventures to develop more rapidly and could also identify and assist potential new import points for both chemicals into the United States. Finally, the federal government must indicate its commitment to maintain the current inland waterway system. However, with no measures that can overcome the geographical dispersion of producers and users, the lack of density in any given corridor, and the already mature markets, significant expansion of the transport of toxic inhalation hazard materials via marine highways is not anticipated.