Design traffic lights at an intersection of a city.  North and South (up and down) are going to be a main highway, East and West (right and left) will be a smaller cross street.  There will be no turn signals and no cross walks.  You only need to build/code one set of lights for each street (one set of green, yellow, and red for the highway, and another set for the cross street).  You do not need to build actual traffic lights or an intersection. 

Explanation:

The following code is written in Java. In order to code this efficiently, I created a class for the trafficLights. The class contains the currentLight, and the streetType as variables and contains a constructore, getter and setter methods, and a method to turn to the next light in the sequence. Then I created 4 objects of TrafficLights for the highways and the streets.

class {

   public static void main(String[] args) {

       TrafficLights highwaySouth = new TrafficLights("Highway", "green");

       TrafficLights highwayNorth = new TrafficLights("Highway", "green");

       TrafficLights streetEast = new TrafficLights("Street", "yellow");

       TrafficLights streetWest = new TrafficLights("Street", "red");

   }

}

class TrafficLights {

   String streetType, currentLight;

   public TrafficLights(String streetType, String currentLight) {

       this.streetType = streetType;

       this.currentLight = currentLight;

   }

   public void nextLight() {

       if (this.currentLight == "green") {

           this.currentLight = "yellow";

       } else if (this.currentLight == "yellow") {

           this.currentLight = "red";

       } else {

           this.currentLight = "green";

       }

   }

   public String getStreetType() {

       return streetType;

   }

   public void setStreetType(String streetType) {

       this.streetType = streetType;

   }

   public String getCurrentLight() {

       return currentLight;

   }

   public void setCurrentLight(String currentLight) {

       this.currentLight = currentLight;

   }

}