EFFECTS OF THE WEATHER-CONTROLLED TRAFFIC MANAGEMENT SYSTEM ON A SINGLE-CARRIAGEWAY MAIN ROAD 1 (E 18)

The purpose of the study was to investigate the effects of variable speed limits and message signs controlled manually according to weather and road conditions on traffic flow on a single-carriageway highway 1 (E18) and the acceptance of the system. The TMC-operator made the control decisions based on the weather and road condition data. There were 22 variable fibre optic speed limit signs and four variable message signs on the 37 km long study road section. The speed limits used were 60 kmph, 80 kmph and 100 kmph. The study used the before and after design for the traffic flow effect studies. The study road data was collected at three measurement points (traffic flows to Helsinki and Turku separately). The control data was collected at a point on the same road west of the study section. Drivers were interviewed at a rest area on the study section. The variable 100 kmph speed limit was used for 4%, 80 kmph speed limit 94-96% and the variable 60 kmph speed limit only for 0.3% of the study time. The signs were malfunctioning for 0-1.7% of the time. The rest of the time the speed limit was 80 kmph. The system affected speeds clearly more than the road surface conditions before the implementation of the system. The following average effects were: The increase of the speed limit from 80 kmph to 100 kmph increased the mean speed of cars and vans out of queues by nearly 7 kmph in normal and by about 6 kmph in good road surface conditions. The percentage of short (under 1 s) headways in queues increased by about half in normal and by a quarter in good road surface conditions. The display of the old 80 kmph speed limit by a fibre optic sign increased the mean speed 2 kmph in inferior, by less than 2 kmph in normal and only slightly in good road surface conditions. The percentage of short headways in queues increased by 8-30% in inferior road surface conditions and by 5% in normal road surface conditions. The 'slippery road' sign with the 60 kmph speed limit decreased the mean speed by 2.5 kmph in inferior and by 3-4 kmph in normal road surface conditions. The percentage of short headways in queues decreased by 18% in inferior and by 6% in normal road surface conditions. The 'slippery road' sign with the 80 kmph speed limit decreased the mean speed by less than 2 kmph in inferior and by at most 0.5 kmph in normal road surface conditions. The percentage of short headways in queues towards Helsinki decreased by 20% in inferior and by 14% in normal road surface conditions. 86% of the interviewed drivers recalled the speed limit displayed by the variable sign. The combination of a 'slippery road' sign and the text AQUAPLANING was recalled by 41% of the drivers about 10 km after passing the sign. The low recall compared to other studies is due to the long (10 km) distance from the sign combination to the interview location. 96% of the drivers considered the variable speed limits to be necessary and 92% considered them as correctly set. 78% of the drivers considered 80 kmph to be the appropriate speed limit in inferior road surface conditions in daylight. Two-thirds of the drivers considered the appropriate speed limit in good road surface conditions in the dark to be at most 80 kmph. The most usual benefit mentioned was improved traffic flow and increased traffic safety. The system functions according to the specified goals when used properly. The drivers accept the variable speed limits and trust their correctness. This sets high requirements for the control principles and reliability of the system. The 60 kmph speed limit should be used more frequently in inferior road surface conditions. The use of the 100 kmph speed limit calls for good weather and road surface conditions. The study has been granted European Community financial aid in the field of Trans-European Networks - Transport.