A method of obtaining data relating to the timing of a transition between phases of a traffic control signal. The method involves obtaining live probe data relating to the travel of vehicles in the region of the traffic control signal, and using the data to determine times at which a given transition of the signal has occurred. This is carried out by consideration of the distance from the traffic signal at which a vehicle waits when stopped at the signal, and a time of passing the signal, as determined using the probe data. Different transition time pairs are analyzed to obtain time differences between the transition times. A cycle time which best fits the time difference data is determined, and used with the transition time data to predict future transition times of the traffic control signal.