Strangely, you are posting this and a SPVM officer got slashed in the face at Bonaventure station here in Montreal just earlier this week.
http://www.cyberpresse.ca/actualites...-iranienne.php
a knife never jams, never runs out of ammo. People should stop underestimating this. I practised Yoseikan style Aïkido for almost 4 years and even then, I will always be scared shitless of a knife wielding attacker.
Keep your distances or just run.