Priority traffic sounds like a good idea until you throw enough bandwidth at the problem. For example, laundry. If you have some garment that you need to wear and wash every couple of days, such as your only work uniform for a messy job, you might keep it aside and throw it into the wash whenever you put on a load. Everything else sits in the basket and waits its turn. This is a perfectly functional system, but it can break down if too much laundry gets the priority treatment. At that point, even though you have a system for treating some garments as special, their express handling doesn't mean anything, because they still don't get washed quickly enough.
The real solution is more capacity, not prioritising. If you wash enough laundry per day, then all of your garments get washed, whether they are high priority or not. It doesn't make sense to bypass a queue that operates at high speed. The same argument applies to anything buffered: theme park queues, to-do lists, internet traffic, highways or airport security. The answer to delays in general is not to create a new, better, alternative queue, but to throw a lot more capacity at the existing queue.
Mokalus of Borg
PS - If you're selling express tickets, though, you have no motive to increase capacity.
PPS - In fact, you are now motivated to clog up the regular queue as much as possible.