Guessing will save only minimal time. Soooooo many cheaters. 4/5 cars in the lane are solo drivers without a pass. Even worse when traffic is backed up, when you'd actually need it the most.

I got so annoyed I contacted UDOT about it. Here is there response:

Thank you for contacting us about the Express Lanes.

HOV violations are very frustrating to us on the Express Lanes team as well. Over time and despite UHP's enforcement efforts, we've seen the number of violators steadily increasing over the years.

We are currently deep in the middle of piloting a modern, camera-based tolling solution that should be much more effective at enforcing the lanes. This new system will allow us to send a bill to motorists using the Express Lane who haven't registered for an Express Pass, with additional enforcement for occupancy requirements planned as well. We hope to begin tests this winter, and if successful will move to a full deployment of the technology shortly after.