But the days of getting stuck in congestion could be a thing of the past - if cities added a fourth colour their traffic lights. That's according to researchers from North Carolina State University, who found that delays at junctions could be reduced by more than 25 per cent by adding a'white' signal. Instead of simply stopping or going, this signal would tell autonomous vehicles to figure out their own way across while human drivers simply follow the car in front. Co-author Dr Ali Hajbabaie said: 'This improves travel time, fuel efficiency and safety for all of the cars on the road.' Scientists have proposed adding a new traffic light colour which uses autonomous vehicles to reduce traffic.