Tests done on original section of forest in setting Winter, Cold, Good, and then repeated as Winter, Cold, Bad yielded up roughly the same results as Summer, Warm, Good, and Summer, Warm, Bad, respectively. Vehicle mobility dropped the same amounts in the Terrain info menu, and unit speeds were the same.
If you feel that forests should be more of an impediment to vehicles, then I guess the easiest thing to do would be to generate scenarios with poorer ground conditions. I played through a quick scenario last night with all other conditions optimal, but with Bad ground conditions. I had Canadians defend vs Soviets. I chose a choke point where the highway ran between two decently sized forests, but also had fairly large areas of brush/fields/open on both sides of those forests, to see what the AI would do. The highway was barricaded and mined, as well as a couple of dirt side roads running through the woods. The Canadians were on foot and supported by M113 TOWs (US M150s), the Soviets all mechanized in BMP-1s supported by T-62s. The AI Soviets avoided both the woods and the barricade and made strenuous efforts to take the objectives from the rear using the clear areas and what side roads there were to advance. Prior to this, most of the time I was playing with ground conditions set to good or fair, and noted the AI had no fear of running vehicles through the woods in those scenarios. I didnít notice the Soviets suffering any apparent mobility casualties when moving through the more accessible terrain. I was wondering if that might be a problem because of the ground conditions being globally bad, the idea being that the forests should be more of an obstacle, but not necessarily everything else to the same degree. I would make note that running through the forest in these bad conditions, even without breaking down, you are only doing ~ 1 kph, which, unless it is a very short distance, is impractical at best, and at worst, you are putting your assets out of the fight.
Then again, it was only one scenario done on the fly, so maybe it doesnít mean anything.
It seems like it might be a ďwell, duhĒ moment by saying make the ground conditions worse, but for me words like good, fair, poor, bad, without any context, donít mean anything, which is why I had to run the tests. If Iím lying in the hospital with two broken legs, but the fellow next to me has terminal cancer, then comparatively speaking, my condition can be considered as ďgood.Ē