NYT today http://www.nytimes.com/2010/02/17/business/energy-environment/17speed.html?th&emc=th
Mearsk Shipping have discovered that by sailing their ships at 12 knots or 20 Knots instead of the previously standard 24knots they save considerable money, even when longer crew costs are taken into account, and also reduce emmissions.
While American States apparently are raising top speed limits it is suggested that driving at 55mph is better than 65mph. Here in NZ a couple of winteres ago I built myself a camper trailer to sleep in the motor camp close to the ski field I like, Cardrona, a field with plenty of beginners runs suitable for an old mad returning to the sport after an absence of several decade so feeling nervous and cautious.
Anyway because I was towing this light camper [ 4ft by 6ft ] I was supposed to not do more than 90k as opposed to the 100k permitted for the car by itself. I discovered despite this limitation my trip time only increased by about 15 minutes on a three hour trip, hardly worth bothering about. Fuel consumption remained about the same and I was saving on the backpacket bed costs, let alone a hotel cost. The trailer paid for inself with about three trips of four or five days each.