Japanese by Example
Learning through examples in manga

Because it's only this road with 〜だけ

からかい上手の高木さん » Volume 2 » Page 24

Takagi convinces Nishikata to spend his summer practicing riding his bike with her on the back.

One day, she asks Nishikata if he’s progressed on his summer homework, saying they should go to his house to work on it.

Since the road back is wide and without cars, Takagi convinces Nishikata to ride doubles to his house.

"Because it's only this road."

Nishikata says he’s riding doubles because it’s limited to 「この(みち)」, this road.