A traffic system was a network of transportation modes. A roadblock was something put in place to block traffic.
In 1996, Rain Robinson was concerned that the driver of the truck she and Tom Paris were following was going to notice them tailing him, since there was zero traffic on that desert road. (VOY: "Future's End, Part II")
In 2267, Spock monitored the traffic on Eminiar VII so as to determine a reasonable place to beam down to. (TOS: "A Taste of Armageddon")
In 2268, Spock noted that the planet Cheron had several traffic systems devoid of traffic. (TOS: "Let That Be Your Last Battlefield")
A planet in System J-25 once had a system of roads indicating a highly industrialized civilisation. TNG: "Q Who")