Traffic flow and level of service on high-class two-lane rural roads in Finland

The basic characteristics of traffic flow on high-class two-lane rural roads in Finland were analysed. The speed-flow relationship was found to be linear. For platoon percentage and mean platoon length as a function of traffic flow loglinear relationships were used. For the mean platoon length as a function of platoon percentage a hyperbolic relationship was used. The percentage of vehicles driven with time headways less than 5 seconds was used as an approximation of the percent time delay (PTD) of the 1985 HCM. The measured flow levels on high-class roads corresponding to a certain PTD-value were lower than the level of service calculation procedure of the HCM would suggest. The probable causes of the differences are the difference of the HCM adjustment factors and those needed for Finnish road and traffic conditions and different speed-flow curves (Finland versus USA).