Traffic-compensated luminance measurement: complementary addition

The document describes the findings from a study, performed as a complementary addition to previous work on Traffic compensated luminance estimation, as reported in MTk4P06467-2, Final report - Traffic compensated luminance estimation (2015-06-24). During the test period the Lseq camera registered many scenes with extraordinary luminance distributions, caused by sun illuminated cloud edges and direct sun in the camera field of view. In the report, we discuss the influence of saturated pixels, field of view of the Lseq camera and the intra-day variation of the visibility of objects in the tunnel opening. Moreover, we show that the luminance value is highly dependent on the centring of the field of view. A rotation of the camera (or diode-based sensor) of approximately 1 degree will — for this particular scene and time of year — result in an average L20 luminance error of 5 percent. One of the principal objectives of the original project was to estimate the impact of active traffic compensation to reduce the influence of traffic on road surface luminance estimation for lighting control. European standard EN 13201 dictates that the luminance should be measured from the road surface — and not the roof tops of the vehicles. In order to achieve this, we need to continuously keep track of the vehicles (using e.g. computer vision techniques) and make sure that, every time we sample a road patch, it is free from occluding vehicles. The basic technology for active traffic compensation was evaluated in the original project. However, the technical evaluation was performed during a time of year when high-density traffic did not coincide with twilight or nocturnal conditions - the conditions of most interest for lighting control. In this complementary project, however, we have utilised the same set of camera prototypes to acquire data under highly relevant conditions. The results show that, at peak traffic hours between 7am and 8am, the mean relative error between the compensated and uncompensated signals may exceed 60 %. The data clearly indicates a correlation between relative luminance errors and traffic flow - where high errors are more likely at times of high traffic flow. Based on these results, we believe that active traffic compensation should be a requirement to maintain errors at a reasonable level allowing lighting control while maintaining traffic safety. In addition to the above, we study the impact of various weather conditions on the road surface luminance. Under conditions with fog and/or snow, our results show that the average surface luminance may double thereby providing opportunities for significant energy savings through active dimming of light sources.

Language

  • English

Media Info

  • Pagination: 33

Subject/Index Terms

Filing Info

  • Accession Number: 01664490
  • Record Type: Publication
  • Source Agency: Swedish National Road and Transport Research Institute (VTI)
  • Files: ITRD, VTI
  • Created Date: Mar 28 2018 10:26AM