This non-referenced answer http://answers.yahoo.com/question/index?qid=20081220144240AA... says locomotives weigh roughly 130 tons, and each carriage weighs 65 tons. That's a lot more than a one ton car.
In any event, doesn't the train being heavier mean that it can carry a much bigger battery pack than the automobile?
Amtrak's newest diesels produce 4200 horsepower, which is just over 3 megawatts. 40 Roadster battery packs (at 53 kilowatt hours per battery pack, and about a thousand pounds per battery pack) would store roughly 2 megawatt hours (35-40 minutes of the diesel at full throttle), weigh 20 tons, and probably cost something under $2 million at Tesla Model S era pricing. The catenary locomotives Amtrak is buying are over $6.6 million each, so the cost to add batteries sufficient for Richmond or Springfield service might well increase the cost of the locomotive by less than 50%.
Charging such a massive ammount of batteries quickly could potentially be problematic.
Recharging will take longer than refuelling a diesel, but if the recharging can be done in under an hour, that's probably tolerable.