Cycle Counter

Hi, I'm currently investigating the best methodology to count cyclists or users of a bike path near my home. I am currently pursuing the idea of a PIR motion sensor with a concentrated field of vision, but open to other ideas. I have also thought about a wireless tripwire, but am unsure about that technology. If I wanted to go the tripwire route, what should I google to start looking at this? It seems like most people are using a laser pointer type thing, but I want something that would be safe to leave alone with idiots that would stare directly into the laser.

Are there any other technologies that are viable and easily interfaced with arduino to sense stuff like this?

Thanks!

How wide is the path? Is it practical to have an IR transmitter and receiver on one side, and a reflector on the other?

Another possibility is an ultrasonic transmitter/receiver.