The dependence of the speed-flow relationship on the traffic volume has been discussed time and time again over the last years. Traffic demand varies systematically and can be explained by daily, weekly, and yearly cycles of traffic volume. The speed behaviour is also subject to temporal variations. These variations do not only depend on the traffic volume, but they also can be attributed to the different desired speed of the drivers. Furthermore the environment conditions (daylight and weather) have considerable influences on the speed behaviour. These temporal variations could be even stronger than the dependence of the speed on the traffic volume. The aim of the research project is to point out the differences is to point out the differences of capacity between the sorts of days (weekday, weekend, holidays) and between the varying environmental conditions. Furthermore the basic relationships of the systematic variations towards the capacity are shown, noticed from the daily and yearly cycles. The database of the project was built by measurements of 15 continuous counting machines at two and three lane carriageways. These measurements were done over a time of three years (1991-1993). The effects of different sorts of days on the speed-flow relationship are not of a uniform nature. They vary on the different counting points. The influence of the environment conditions are shown by comparison of the speed-flow diagrams, with the permutations light/dark and dry/wet. By the analysis of the measured time-series the general trends of the velocity and traffic volume development are shown. It is also shown that at the same environmental conditions higher velocities are observed in winter than in summer. (A)
Abstract