Traffic is my chief concern. I'm always convinced there's a pickup barrelling up the road towards me that I'm just not seeing/hearing. I once flew round a blind corner at speed when I was 14 or 15, and I landed on the front windshield of a Toyota Starlet, with my frame totaled and a couple hundred pounds (a lot of money to a teenager back then) worth of damage done to the car. I don't want to ever repeat that experience.