MAIN ROAD 4 LAHTI - HEINOLA JOURNEY TIME MONITORING AND INFORMATION SYSTEM FUNCTIONAL EVALUATION

This study consists of a technical evaluation of a journey time monitoring and information system on the main road 4 between Lahti and Heinola. The system was installed during the summer of 2000. The study is not intended to an impact assessment but a description of the system functionality and principles. The technical evaluation is based on the reliability of chosen equipment and on the information given to the road users. Between Lahti and Heinola the main road 4 is a 28 kilometres long three lane road with two lanes alternating between each directions between the motorways from Helsinki to Lahti and from Heinola northbound. The traffic is congested regularly during the summer weekends. The typical Friday evening congestion northbound lasts for four hours and the average delay is fifteen minutes (normal travel time is 20 minutes on the link). On the worst 15 minutes of typical congestion, delay is up to 25 minutes. During the Midsummer congestion delays were up to 35 minutes. The Sunday afternoon south-bound congestion is not as severe. Typically the link is congested on the end of the motorway south from Heinola. Average Sunday congestion lasts for two hours with an average delay of under 10 minutes. The traffic is monitored using automatic licence plate recognition. When the same licence plate is seen by two measurement stations, the vehicle journey time can be calculated. The system comprises of four measurement stations. The average journey times between the outstations are the basis for the values displayed on the variable message signs. The speed limit on the link is 100 km/h. Due to the heavy traffic allowed only to drive at speeds up to 80 km/h the normal average travel time is given as 22-27 minutes. The five minute difference in travel times equals to the 20 km/h difference in travel speeds. Technically the system has functioned rather well. Due to a system malfunction on four different occasions the information given to road users has been incorrect. During the malfunctions the system has however monitored traffic properly, the information has just not been transferred to the signs due to telecommunication failures. The current software does not predict the travel times. The given information is solely based on latest measured travel times. When the congestion builds up, the retrieval of travel times is delayed more and more. Therefore the values displayed on the VMS are too small in comparison to the current situation in the beginning and too big on the end of the congestion. Maximum error at the beginning of the congestion has been 9 minutes, meaning the time spent on the link has been 9 minutes more than what was displayed on the VMS to a road user. Usually, the time window during which erroneous values are shown lasts for 20-30 minutes. The lack of a prediction algorithm has been compensated by adding manually a constant to the travel times during the normal congestion build-up on Friday evenings. The corrected shown journey times have been on a par with the real measured journey times. A short-term prediction function will be added to the system. After the implementation of the function, the displayed journey time values will be more precise compared to the real journey times. Also, publishing the journey time information on the internet for the road users and media, can be implemented before the summer of 2001. Improvements on technical maintenance of the system will be done: the system shall automatically alert maintenance group in case of a faulty or malfunctioning equipment or in case of loss of performance. Studies on the possible effects of the journey time information on traffic behaviour, attitudes to congestion and route choice, should also be carried out.