Yep, it's the dogs! If you get a later 2005 BM54 it's improved even further with Dynamic Routing. This feature takes the TMC data (length and time of delay, bad weather, closed roads, roadworks, faulty traffic lights, etc.) and assesses all traffic and route options. If a quicker route is found it automatically reroutes. Of course it's only as good as the TMC data source, which is generated from vehicles fitted with special transmitters, traffic monitoring cameras, etc. There tends to be a 10 -15 minute delay i.e. some traffic incidents aren't reported in time and sometimes they show as still present when they have cleared.

Still it's a lot better than standard radio broadcasts, and it's saved me being sat in major traffic jams on many an occasion