I recommend not considering a knife as a self-defense weapon. A knife is a very useful tool, and there are any number of good, valid reasons to carry one, from cutting a boot to repair a sidewall tear to prepping a tube for a patch to opening those confounded little rubber cement tubes to removing metal flakes and debris from brake pads. But discussing any tool, be it knife or tire iron or bike pump, in terms of pre-planned defense or use of force, particularly in a public forum, can make that tool look a lot like a deadly weapon in the law's eyes. Get non-lethal deterrants (like spray or a stun gun) appropriate to the laws in your area. Carry other tools, like a pocket knife or wrench or bike lock, as appropriate for your mechanical needs. You should also practice with any thing you might use defensively. 4AM is a crummy time to be learning how to use something, or doing it wrong and hurting yourself.

I am not a lawyer, this is not legal advice. I'm just a fan of sharp tools, and enjoy the right to carry them for appropriate purposes.

I also believe in stopping for stop lights and otherwise obeying laws of the road as they are written. Morning commutes aren't good places for protests, nor will protesting them in the road have any impact on changing them. Make your voice known to your local representatives and work to get the ordinances changed.