Added weight from a second powertrain can limit a trucker's haul -- increasing per ton transport costs
That's exactly the problem with today's hybrids - from the Toyota Prius to the trucks mentioned in this article. Why? There is absolutely no reason for having TWO drive trains.
The solution? I theorized about this in 7th grade for a science fair project (and still pretty sure it could have been done even then), and have written about it recently on this blog too - a single electric drive power train that is driven entirely by battery power; the batteries can then be recharged either through plug-in, or through a small generator that kicks in only long enough to recharge the batteries while the vehicle is in full use.
In fact, that should be even more feasible now than it was in 1994 since we have all these technologies to reclaim energy from braking and other activities and divert that power into the batteries.
Sadly, it looks like the first such vehicle will be GM's Volt due to be released in 2010.
Unfortunately, for the trucking industry - you have a lot more rugged condition that the vehicles need to stand up to - mostly for construction site conditions and any other off-road condition. (They face the same basic problem that off-roaders face too.) This makes it harder for the electrical drive train, which has to be protected even more, especially against water. I personally think that at least the vehicles that need these kinds of ruggedness will be the last to go electric. Semis, and all other road vehicles that only need normal road conditions will be there pretty shortly, in my opinion. (That is only based on my limited knowledge of the mechanics behind it; not on any actual industry info. But it should be what happens.)
[Edit: In another story, Porsche had one of these "serial hybrids" in 1901. So it was definitely achievable in 1994.]