Traffic Law 101:
1) If a guy with a uniform, gun, and badge turns on the lights and pulls you over, he owns you. If he said you broke the law, regardless of whether he is right, you broke the law.
2) In the event of (1) above, act like you are guilty and say you are sorry. Don't be a smartass. At worst this will get you shot so you got off easy with an $1100 ticket.
3) Ignorance of the law is NOT a defense. e.g - I will bet the HOV lane was clearly marked as HOV. It may have even explained that this means you need more than one occupant. If there are no other signs than this then it means that these are the minimum requirements: more than one person. Any reasonable person (yes, this is a legal precedent) would know this and assume that all bets are off if this one and only rule is not followed.
4) It is not the governments responsibility to tell you all the inclusions, exclusions, and things legal or illegal in the HOV lane or any other roadway. For example, any reasonable person would know that it is against the law to drive down the HOV lane naked in a convertible shooting a .45 cal while drunk. This will get you thrown in jail. They should not have to put this on a freakin' sign just like they should not have to put up a sign saying it is a 24/7 HOV lane.
What really amazes me is that you would even think you have a fight in this case. The judge is probably going to tell you something close to what I just wrote. But if you want to waste your time and money, by all means, go ahead. Just keep in mind that it is people like you who make for the overly litigious world we live. It seems we are coming to a point where every simple logical rule has to be explained in detail otherwise people bear no responsibility for their own actions.
Oh well, I bet you don't hop over into that HOV lane anymore