ORIGINAL: Bil H
That is map dependent... the map designer can decide whether to allow access to woods for vehicles or not... in fact in the map editor, in addition to movement effects; fire effects and spotting effects can be specially adjusted to account for the effect you are looking for. What I would do is make woods (heavy woods) not accessible to vehicles other than on roads.. but I would then mix woods and scattered trees, which you could allow vehicles to enter. So creative use of the map editor can indeed supply the effect you are looking for.
Yes I gathered that from my map design effort for HTTR (my Cologne map/scenario), so I experimented with the vehicle movement speed in woods, and set it to extremely low values (1-3). In HTTR the engine did not cater for the last "mile" to the point of attack, though, that means a tank unit would even attack through dense woods, resulting in an attack to be delayed by up to 10 hours or more, because the tanks had to make it through the rough terrain, first.
That makes me wonder, now, though: Currently, with the BFTB engine, tanks cannot enter dense woods (heavy woods), right? So, are you talking about placing wood and scattered tree layers next to each other, if you're suggesting to "mix" layers?
Whatsoever, from what I gathered, from various sources, including vet accounts, pictures and original footage, tanks could and can access woods, if the ground is not too muddy/sticky. There's a video of a T-34 being pulled out of a mud hole in Russa a few years ago, on youtube. The mud basically preserved the tank, its tracks and wheels were fully working, and I didn't spot any rust. Since it was in the middle of a wood, question is: how did it get there? [;)]
EDIT :
Ppl may wonder why I'm so persistent here, regarding accessibility of woods or rougher terrain ... I just think it's more realistic, plus it offers different approaches for the player. If your tanks can cut through 400 meters of dense wood, instead of approaching the enemy's AT guns in a village with a frontal attack on the main road, and if such a tank unit is then able to use the trees as cover/protection against AT shells/spotters, it will make a major difference.