The Dutch Department of Public Works, Directie Oost-Nederland (RWS-ON) took it upon to answer whether the presence of illumination on motorways as compared to motorways without illumination leads to increased utilisation. In 1995, RWS-ON installed illumination along the A50 motorway. As this was known well in advance, a study could be launched whereby the situation before and after the installation could be compared. TNO-INRO was commissioned to aswer this utilisation question. The following `traffic variables' were included in the analyses: capacity, headway, and distribution across the lanes. The only change in the before and after situation was that the right-hand lane was used more after the illumination had been installed and with that the left-hand lane was used less when traffic intensity was lower. It was also shown that: (1) speeds did not change significantly; (2) brief headway did not increase when behaviour was noted; and (3) that the capacity estimator did not indicate any differences. Therefore, the general conclusion may be drawn that illumination does not lead to improved road utilisation under free-flow conditions. (A)
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