Re: How can I increase my confidence when hacking?
Take him for walks - get yourself a 12-foot line and pressure rope halter and walk him round your usual hacks. It's great for his confidence to see you on the ground as his leader, and it's safer for you because you have plenty of space with the line to stay out of the way if he freaks. If a bike comes by, keep calm, let him have his paddy (but don't let him tank off), and then continue the walk as normal. Don't get on his back until both you and him are completely happy and confident with bikes.
My own horse isn't great with bikes but unfortunately where we are every week a group of dirt bikers come by and sometimes I am out walking him when they pass. I take him off the trail, let him freak, and then keep walking. Any desensitization work you can do with push bikes, hairdryers, leafblowers, loud noises etc. is great because it will get him used to loud, moving objects. If you know anyone with a motor/dirt bike, see if you can borrow it to get him familar with it! Be aware that this will take potentially a long time and should be done gradually, so as to keep him happy at all stages. If at any time he's unhappy, take a step back.
When you do begin to ride him again, please please remember that getting off is not a case of 'him winning or you losing' or something that will knock your confidence. It's a matter of safety. Falling off and injuring yourself or your horse will knock your confidence - getting off and leading him will build it and keep you both safer. He'll also be able to see you more as his leader on the ground and take comfort and courage from you. If you ever feel afraid, get off.
Get in touch with a local Natural Horsemanship trainer - eg. Parelli, or Monty Roberts (Intelligent Horsemanship) - who can help you conquer your horse's fear and will do great things for your confidence too! Good luck. :)