I just want to put it here since my mind can't relax if I didn't say it out. Pardon my English.
In my opinion, Wataru is dead (or he's still unconscious). There is no way a city can develop that much in 3 years (even though this is a fiction but if this manga is inspired by a novelist like Kafka I think it has some meaning behind the absurdism). He's in the 'after-world'.
So every time he says "I'm hurrying to live" I think he means that he wants to find the meaning of his life. As a funeral officer (idk the English word) sometimes he wants to know how is life after death will be like. So he's hurrying to live and he rides his bike to the 300 because his friend told him whoever rides his bike over 300 will see another world.
Some people think that he's hurrying to death because what he did seems like a suicide to them. Even so, he always dismisses the thought and says "I'm hurrying to live". He believes what he did is different from the other people in the Kingdom do (where they treat lives lightly).
The point is, sometimes all of us wonder what will happen to us once we're all dead. We only hear from the other people what is the after-world going to be like (heaven or hell or something) although every one of them has not been there yet. So their opinion is not credible either. But when we live our life without goals or meaning in it, we will feel restless and empty. It's like running on a path that you don't know what's the end will look like.
Will you be praised for doing a good job while running on the path. Or you will be punished because you've done bad. But what's good and bad again?
So Wataru, instead of finishing his track like how it should be, he goes straight to what he believes as the end of the path. He wants to know the answer by himself. Because he believes that his life holds meaning and not empty, unlike the people of the kingdom do.
Now I can go to sleep. （/TДT)/
It feels like I read the manga version of a German Novel in the 20th Century ლ(´ڡ`ლ)