The old DOT-111 rail cars carry about 700 barrels of oil but because of safety concerns they are being phased out for newer, safer DOT-117 oil rail cars which can carry about 675 barrels of oil.
We will use 700 barrels as a round number to form a basis of comparison:
1 rail car tanker = 3.25 truck tankers = 700 barrels = 111,000 liters = 29,500 US gallons = 117,500 US quarts
As you can see below there are different capacities of DOT-117 rail cars:
Canada ships about 150,000 barrels of oil PER DAY on rail, mostly from the Alberta Oil Sands, because there is no more pipeline capacity remaining in the system: