This report presents suggestions for new speed-flow relationships for motorways (MV), low standard motorways (4F), oncoming lane separated highways with grade separated intersections (MML), oncoming separated highways with at grade intersections (MLV), and two-lane highways. The suggestions are based on measurements from the Swedish Transport Administration’s (Trafikverket) traffic measurement system TMS in combination with model calculations. The TMS data have, for each road category, been quality checked, processed and analysed. The data material is presented as speed-flow diagrams for passenger cars, buses and trucks without trailer, and trucks with trailers. A comparison of the Swedish Transport Administration’s current speed-flow relationships and the TMS measurements was then conducted for each road category. The average free flow speed for trucks without trailer has in general increased on motorways (0— 1 km/h), on low standard motorways (up to 3 km/h), on oncoming separated highways with grade separated intersections (1—2 km/h) and on oncoming separated highways with at grade intersections (0.5—5 km/h). However, there are some uncertainties due to difficulties to classify trucks without trailers in the TMS system. There are also cases in which the speed for trucks without trailers has decreased up to 3 km/h. The trend does not apply for two lane highways for which the speed for trucks without trailers has decreased with 0.5—2.5 km/h for all speed limits except 100 km/h. Another trend is reduced speeds for trucks with trailers for all road types except low standard motorways. The decrease varies between 0.5 and 2 km/h with some few exceptions. The underlying reason for the general increase is unclear. The speed on two lane highways continue to decrease. The revision of the speed limits system seems still to imply decreased speeds on two lane highways. The trend with reconstruction of two lane highways to oncoming separated highways is still ongoing. This implies that the characteristics of the remaining set of two lane highways have changed since roads with good alignment and higher flows are rebuilt into oncoming separated highways. To utilize data from the TMS system in combination with the national road database (NVDB) to revise speed-flow relationships have some limitations which affect the accuracy of the results. The TMS measurement system is designed to measure traffic flow in a representative and statistical correct way. The placement of the measurement points does not necessarily result in representative travel speed on road links, some locations are e.g. close to intersections. Another problem is that the TMS system only collects cross-sectional time mean speed aggregated on an hourly basis, which imply that a transformation to space mean speed is required. There are transformation equations for this but these require the variance in space mean speed (or time mean speed) which were not available. There have also been some problems related to the classifications of roads used in the Swedish Transport Administration’s speed-flow relationships and the national road database (NVDB). NVDB classifies roads based on their geometry and not how the traffic process looks like. Furthermore, the current sub road classification is no longer suitable. For example, to divide two lane highways with respect to road width does not seem to be relevant anymore and a division based on the type of traffic (commuter/long trip) seems to be more relevant. Next step should therefore be a review of the road classification based on the knowledge from recently conducted research projects and the current revision of the speed-flow relationships. There is also a need for development of definitions and methods for a concise and unique translation of the attributes in NVDB and the road classification utilized for the Swedish Transport Administration’s speed-flow relationships. (Author/publisher)
Abstract