Vehicle-induced turbulence near a motorway

In spring 2001, turbulence measurements were carried out adjacent to the motorway from Mannheim to Heidelberg in order to determine the intensity and range of vehicle-induced turbulence compared to the natural atmospheric turbulence. It was found out that the location of the motorway on a 1 m high dam leads to mean vertical winds in the vicinity of the dam (distance of 3 m). The windward/lee difference of the mean vertical velocities, wwind−wlee, normalized to velocity perpendicular to the motorway, u, amounts to about (wwind−wlee)/u≈0.1. Due to the different surface properties, kinematic heat flux at 4.75 m height in the lee vicinity of the motorway (distance of 3 m) is higher than on the windward side by up to 100%. However, comparison of the resulting thermally induced production with mechanical production of turbulent kinetic energy (TKE) shows that the higher kinematic heat flux is not responsible for the lee increase of standard deviation of the vertical wind speed (σw) or TKE. The significant increase in the turbulence parameter σw and TKE in the lee is restricted to an area close to the ground less than 50 m away from the motorway. Near the motorway (distance of 3 m), lee values exceed the windward values by about 70% for typical TKE values of e≈1 m2 s−2 and by about 50% for typical σw values of σw≈0.5 m s−1. Analysis of the energy spectrum reveals that this additional energy occurs in the frequency range starting from f>0.1 Hz. The lee/windward difference of the TKE values exhibits a distinct functional relationship with commercial cars (R=0.77) and a moderate relationship with passenger cars (R=0.58) such that the increase of TKE can be attributed to vehicle traffic.