I put this in another thread, but I feel it's important enough to get its own topic.
You could spend forever making minor tweaks and adding features, but my biggest usability suggestion would be to have graphical sub-menus rather than a list. To read a list takes your eyes off the road for too long and with the bumps, it's easy to select the wrong item. I've whipped up a new sub-menu screen in Photoshop.
Note the new items: Car stopped (so common, but missing) and Slippery (instead of Oil spill, which works for any liquid, sand, gravel, black ice, etc.)
VP, Product Management (for a software company)