This is the 969th most frequent Chinese word.
一路
"All the way" or "the entire journey."
In this sentence, "一路上" means "along the way," signifying the course of our journey.
我们一路上都很开心。
We were happy all along the way.
Here, "一路" is figuratively used to mean "all the way" or throughout, regarding ongoing support.
我会一路支持你的决定。
I will support your decision all the way.
"一路" is used here as part of the idiomatic expression "一路顺风," wishing someone a smooth journey.