The Compass Card may have been years late in coming to Vancouver, but TransLink’s reaction to my story last week of being charged for a three-zone trip without leaving a station came swiftly.

A spokesman told me that the day after the story aired, two teams of engineers were assigned to figure it out. They spent eight hours in their testing lab, using the data generated by my Compass card to recreate exactly what happened.

Here, in a nutshell, is their conclusion: the $194-million Compass system worked as it was designed. Unfortunately I had fallen through a crack that is only open during the current phase of the Compass Card rollout - when the fare gates are open.

And when the fare gates close, the "user error" that resulted in me being charged $4.20 will be incredibly rare.

Here’s what happened.

We were covering a story about a new phase of the Compass Card rollout. We needed some footage of the Compass Card in use, and I offered up mine. I went in and out of the station four times, tapping in and out each time, for no charge. The CTV cameraman shot the events from different angles. Everything worked as it should have.

On the fifth time, records show I didn’t tap in. When I tapped out, the Compass system noticed that I was not in their system, and assumed that I had entered the Skytrain improperly. In that situation, it bills the passenger - who it feels is likely a gate-jumper or fare-evader - the maximum fare that could be owing: three zones, or $4.20.

In isolation, that would be normal: the system is billing me for the maximum trip it believes I could have been taken. 

But in my situation, I had just tapped in and out of Stadium Station minutes before. It would be impossible for me to have gone more than one zone in that time. I believed, if anything, the highest I could be charged would be $2.10, the discounted Compass one-zone fare.

In a phone call with the customer service desk, the operator did much better than that - she refunded the entire cost. 

And in a subsequent conversation with TransLink communications director Marc Riddell, Riddell explained why Compass would have handled this correctly if it was fully operational.

Right now, it’s possible to walk onto the system, even if you intended to tap in, as I did. That means it’s possible for someone to walk off, tap out, and get charged.

When the gates close, they will not open unless someone taps in correctly and pays their fare. That means nearly everyone on the Skytrain, Seabus or West Coast Express will be in the system, and tapping out will gauge the correct fare.

I say “nearly” because there may still be the chance for other honest mistakes we haven’t seen in action yet. A person following someone too closely through a gate, for example, or someone walking through the accessible doors and forgetting to tap in. 

Riddell says those will be very rare situations, and this is a problem that will not affect the vast majority of fare-paying customers.

I asked: will there be a system that warns the registered card users when they’re being billed for a trip they may not expect? An e-mail to the e-mail address connected to their card, for example?

That may be possible, he said -- but not something being done right now. TransLink's strategy has instead been to be open about the possibility of being overcharged, mostly in the situation where the rider doesn't tap out. He says 70 per cent of users are doing it right. The rest have to learn -- a learning curve that will get a lot steeper in 2016, when the gates start working.

So until those gates close, customers should keep checking that online account to make sure an honest mistake doesn’t become a charge.