You need to leave much more space for merging and pulling out in traffic. Many people that drive 240D's on a daily basis are familiar with the "slingshot" method utilized to pass traffic on two lane roads. This method requires knowlege of the road being travelled, when you are approaching a passing zone you drop back a couple hundred yards and then use the space to accelerate the car to a safe passing speed while hoping the passing zone will be clear. If the passing zone is not clear you have to jump on the brakes and resume your place behind the slower driver...
HAHAHA! I have to do this with my 300SDL as well to pass someone at 40 or 50 to gain enough speed (70 or so) to pass them quickly enough..
Thats one of the things that makes diesels so great, these little quirks.