No, as has been stated many times, railroads do not give any bonus to forests.
What railroads do is increase the output of any terrain improvement by 50%, rounded up. As it happens, this always works out to a +1 bonus in the standard game. For example, let's say you have irrigated a floodplain wheat. The floodplain gives 3 food by itself, +2 for the wheat, for a total of five. Irrigation increases that by +1, to six. Now you add a railroad. If railroads increased the output of the whole tile by 50%, you would expect to get 9 food from the tile. But it doesn't. It adds 50% of the irrigation bonus, rounded up, or 1*0.5 = 0.5, which rounds to +1. Railroaded, irrigated floodplain wheat produces 7 food, the highest in the game.
The highest value terrain improvement bonus is a mine on a hill or mountain, which gives a +2 shields. But of course 50% of +2 is still just +1, so railroading a mined hill still gives you only one additional shield.
Unless you play modded games, you can just think of railroads as giving a +1 improvement bonus, and you'll come out the same.
But the shields from a forest are not coming from a terrain improvement, but from the terrain itself. Therefore, there is no bonus applied from a railroad, as has been reiterated several times. Similarly, the floodplain wheat we mentioned above gives 5 food without irrigation. If you put a railroad on that non-irrigated tile, it still gives "only" 5 food.
....I know that....

I guess I was just trying to say the same thing you just did...I'm just not one with words
