(To expand on what I wrote: There's surely a risk of some forum users getting pissed off with other forum users in ways that would never have happened without an "off purpose" forum - imagine something like the way that the intelligent design thread might be in 10 pages.
There are a huge variety of backgrounds on the boards, united by a common interest in road safety. So far we all seem like a civilised bunch
but as the boards become more popular there will be some coming with shorter fuses. Religious debates (although how one anyone with scientific training can actually 'debate' against evolution and keep a straight face is beyond me) and suchlike can only lead to unwanted tension and distract from more useful discussion.
Of course, you could argue the converse, which is that this will lead to a greater sense of community, which is what I assume your motive was...)