Originally Posted by lesdunham
It would be a shame to say I knew better ... after the fact.
Always wear a helmet when riding. The human skull can be damaged in a natural fall, add 14 - 20 mph to the equation, asphalt or gravel, and complicate it proximity to moving automobile and it is dangerous enough. Reduce the seriousness with a helmet. Concussion, broken collar bones, and scrapes will heal. Permanent damage is what you need to prevent.
The proximity to moving autos is the real helmet deciding factor for me. I'm more likely to get in a fall situation if I have to make an emergency manouver to avoid getting doored, hooked, etc. I always wear my helmet when street riding.
The speed factor is why I wear my helmet on the MUP. I've been in some high speed wrecks, and feel that the damage my brain bucket took was better than having smacked my bare dome on the pavement.
If I was worried about "natural fall" damage while riding across the parking lot to the grocery, I'd also wear my helmet when I was walking to the video store, in case I tripped on a crack in the sidewalk.