Owl City - Cave In Lyrics Meaning

At first the song seems to be about running away from home as a child.
"I'll ride the range and hide all my loose change in my bedroom, cause riding a dirt bike, down a turnpike, always takes it's toll, on me"

yes, it's a pun about the turnpike, his songs are full of these puns, but there is meaning hidden behind them.

if a child wants to run away from home, he has to hide all his loose change in his bedroom where his parents won't find it.

when he says "I'm history" in that line he's trying to tell his parents that he's serious about this and there's no stopping him.

"I've had just about enough of quote 'diamonds in the rough'
Because my backbone is paper thin
Get me out of this cavern or I'll cave in"

he's saying he's had enough of trying to find the good in bad situations, and that he can't take anymore of being in that house, the house being the cavern he mentions.

"If the bombs go off, the sun will still be shining
Because we've heard it said that every mushroom cloud has a silver lining
(Though I'm always undermining too deep to know)"

He's saying that if the family has a serious issue, the bombs going off, he'll be okay because every bad situation has a silver lining of sorts. his would be running away; but he's saying that from a child's point of view they wouldn't think that, it's too deep to know. Which is why many kids don't run away, despite wanting to, and why many kids commit suicide. When he says he'll cave in, that is what he means.

"I'll soak up the sound try to sleep on the wet ground
I'll get ten minutes give or take
'Cause I just don't foresee myself getting drowsy
When cold integrity keeps me wide awake"

he's talking about insomnia there, and how kids tend to lie awake and think. he's using very vivid pleasant imagery there to the point of being surreal, showing that the kid hasn't really run away, but is instead imagining it and how great it would be.

at the end he's talking about how if he crashed he would likely die/kill himself, so he's keeping "his helmet" on for safety. his helmet is likely a metaphor for the emotional walls we all put up to protect ourselves from others.

Finally, he states that he will keep his eye on the task at hand, survival, and his ideal future. He's talking about the long journey of life that he's persevering through despite suicidal thoughts.

so that's it. it's a song about childhood crisis at home that leads to suicidal tendencies and the journey of surviving those young hardships for a better future.