A method controls vehicular traffic on a one-way roadway. A hardware sensor detects vehicular traffic on a roadway. A hardware traffic control device determines whether the vehicular traffic on the roadway has been moving exclusively in a first direction during a preceding period of time, such that the roadway is a one-way roadway on which current vehicular traffic is authorized to travel only in the first direction. The hardware sensor detects an errant vehicle that is traveling on the one-way roadway in a second direction that is opposite the first direction. In response to determining that the errant vehicle is traveling in the second direction on the one-way roadway, a warning signal is transmitted to vehicles, other than the errant vehicle, on the one-way roadway.