过路 = cross the road 过路即要小心, crossing the road, [one must] have to be careful. 路过 = pass by (doesn't have to be by road). For example, 路过貴島 "I pass by your esteemed island" obviously not by road transport.

we seldom use " 过路"，in most case，过路 is adj ,such as 过路的，过路客，过路人，过路费， in most case 路过 is vt, vi, adj, such as 他路过（vt）上海, 他从上海路过（vi）,(从.......路过) 路过的（adj）地方太多，我都忘了

路过 is a verb.It means passing by somewhere.Like 我刚刚路过一个邮局。 We seldom use "过路". You might say toll as "过路费" in Chinese, I think.

过路即穿越过马路，路过即从此处经过。

usually, 路过represents an action that happened just now, means that I just passed someone or somewhere; and 过路 however, means a passer-by and most of the time we rather call passer-by as 过路人