Confidence issues with Rowdee

I have a 4 yr old qh named Rowdee. I have owned him since he was 4 months old. I love this horse to death!! I am very, very attached to him! I started him last year as a 3 yr old and he was going really good. I rode him from July to November. About the last time I rode him in November I was crossing him over a pile of logs and he got spooked and jumped up in the air away from the logs. I fell off, well more like launched off up in the air and almost landed on my feet. Not really a big deal but it happened so quick I had no time to react. I got back on him and rode him around our feild he did fine after that. Fast forward to this year. Started riding him again he started off prety good a ltitle unconfident but still remembered everything I taught him from last year. Well come to find out he is afraid of traffic that goes by my house. I live along a busy state route with semis and motorcycles going by. His pasture is right beside this s.r. So I figured he should be prety much used to it right? WRONG! I was riding him about a month ago or so and a hugh loud semi went by and let off the jake break! He spooked bolted and tried to run off with me so I tried the one rein stop which I thought he was pretty good at when he was not scared. Didn't work out so well he jumped sideways about 3 or 4 times and I started to loose my seat. Then he bucked and off I went! Didn't get hurt then but let me tell ya the next day or two I was so sore! I had a hugh bruise on my arm where I must of hit the saddle horn. And of course my pride and confidence were both shot! I have ridden him twice since then and only at a walk and not at all by the road where the big trucks go by. He is just so calm normally but if something scares him LOOK OUT! Or HOLD ON, I should say! Everyone is telling me that he is immature and will grow out of it. Would love to send him to someone to put miles on him, but I really cannot afford that right now. So there is my story about my confidence issues. I am hoping I can come over come them!! I know I can do it!! I cannot give up on him or myself!