Cameras located on the A19 trunk road at Hedworth lane south of the tunnel and the A193 north of the tunnel record the number plates of vehicles as they pass. Cameras located at the north and south exits of the tunnel record the number plates of vehicles as they leave the vehicle tunnel. A comparison of the records is done as each vehicle leaves the tunnel to compare the time that it was recorded on the approach to the tunnel with the time it leaves in order to calculate the current journey time in each direction. The calculation takes an average of all recorded timings within a 2 minute period and outputs this figure to a live file for transmission to the website and a log file for historical information gathering.