Cost conveyance is also holding short sea shipping back. Water is the cheapest way to go by far in terms of tons per mile because ships/barges can carry a lot of it. But cheap is only a concern for low value, high volume/weight cargos. That is why grain, coal, petroleum, etc transportation over distance is by water or rail. High value cargo (containers, cars etc), cost can be passed on to the consumer/buyer very easily because time and inventory management are primary concerns (Just in time logistics). Also, at the end of the day, cargo still has to get on a truck to the final destination. The last figure I recall is 500 miles (New England to Chesapeake Bay) or less was cheaper to truck because of the cost to transfer through a port, as previously mentioned.