Good idea ...up to a point.
I do realise that road transport does have it's advantages, and lets face it, it's just the modern version of the horse and cart. It's just when you are going down a moronway .....motonway ....motorway even, you see all the hundreds of lorries and start to ask yourself
'How many of these are actually necessary??'
'If other forms of transport were to get themselves sorted out, how many of these could be taken off the road?'
'How many lorries could, say, a freightliner replace??'
And so on.
(In a similar vein, a year or so ago in response to rising fuel costs, Maersk, the world's biggest merchant shipping operator, adopted 'slow steaming' on all voyages that were not time-sensitive, reducing from an average 25 knots to 14 knots. In the first nine months they saved $1/2 billion.)
I'm a great advocate for using rivers and waterways a lot more, (after all, I live next to the Clyde which has been chronically under used for decades, as well as the local canal, which was only restored 10 years ago), although I do remember hearing somewhere that in actual fact, if you were to sail over the Atlantic on a liner, then it would have produced as much pollution as an airliner.
Yet again, the passenger per ton of ...crap comes into play here though and it'll be cleaner over all. Sort of.