The sheer number of trucks on the road is appalling.  (So is the number of cars, but that's not the issue here.)  Something needs to be done to greatly reduce that number.  Merely improving the fuel mileage of vehicles that are needlessly consuming oil and polluting will only slightly lessen the problems they cause and will not approach solving them.

What's the average fuel efficiency per container on a truck versus a train?

And even if it is better, more container trains means more trouble for Amtrak and other passenger trains, who often haveta share the lines, and though the government requires the container lines to give way to passenger trains, it hardly ever happens.

It's responsible for the vast majority of the time delays by Amtrak.

Re fuel efficiency, there's no comparison between trucks and trains.  While a train engine uses more fuel than a truck engine, a train can be over 100 cars long.  Trains are far more efficient than trucks.

Of course, the fundamental problems here, as elsewhere, are overconsumption and overpopulation.  Eliminate these problems and there wouldn't be anywhere near as many trucks OR freight trains.

Slowing down from 75 to 65 is a start, but 55 is even better.  How about a national speed limit for trucks AND cars of 55 mph?  

With 55 the ENFORCED law, highways last longer, less air pollution, and perhaps consumers will no longer value "performance" over fuel economy.  Besides, with wireless connectivity and DVDs, there's no reason to blast at 75+.  Might save a few more lives as well.

Bring back the Double Nickle!