You used to need to have your ID card validated or whatever at the Security and traffic office so that the boom gates open for you, but from last year onwards you dont need to do that, but like KP said, if it doesnt seem to work you should go get them to do it.
I've been told/I find that the trick is to make sure you do it at the same time, or at least within like 2 secs of each other. Otherwise you're screwed. The gate on the left is for small cars, the right for bigger ones.
My friends and I were always on point with this, but then I got a new carpool partner and he sucks balls. Except I think security is always watching carpool coz they've always automatically opened up the gates for me, without me even pressing the button.