After all the comments about the various states banning filtering (Lane Splitting) makes me glad to be in Belgium.
Previously it was done, but never mentioned in the law. That has now been amended. The law states that you can filter if you are travelling within 20 kmph of the other traffic & under 50 kmph. However I am the slowest person while filtering - A colleague of mine has topped over 100kmph in the traffic!
I think it is all down to the safety margin every one has. I spent a number of years off the bike, so my reactions are slowed. That and the desire to get back to wife & kids means I have a rather wide safety margin, so I do not travel as fast nor go through gaps as perhaps I could.