At BMW factory in South Carolina there is a Z3 Safety Shell Exhibit that shows off some of the design and technology BMW is using to make these cars as safe as possible. One of the improvements they are especially proud of is the yellow bar you see running horizontally across the door.
It looks simple enough but this bar is designed to protect the occupant by spreading the impact in front of and behind the driver. At the exhibit we were told that this could easily make the difference between walking away from an accident or not.
Okay forget marketing hype, Mike Dwyer saw this device work in real life. “I had someone run a red light and hit me directly on the drivers door at about 35mph. Only a few minor nicks for me, but the M roadster had the back left wheel tweeked and the total bill was almost $12k”
Looking at this picture you can see that the door was the impact zone. But notice the raised ridge (and picture that yellow bar from the safety shell exhibit).