I'm looking for the sentence which is the opposite of "The traffic is busy." The sentence I want to make is, "The traffic to the downtown is usually very busy during rush hour, so we should leave very early around 5 o'clock when the traffic is light/ the traffic is empty / the traffic is smooth / the road is empty. Which sentence is the most natural English to say? Or if there are other sentences, could you tell me? I've checked it myself, but I'm sitll not sure which is the appropriate sentence.
I've never heard or used "busy traffic" in this context. Rather, the roadway is what is busy with traffic. So I would use: "The traffic is usually heavy during rush hour," which would make the opposite "light traffic."
I think "traffic flow is smooth" is how you say it in English