Observations at a semi-urban, priority T-junction at the London-Southhampton trunk road (England) indicate that the gap acceptance behavior of drivers in the left-turn merging maneuver differs significantly between daylight and street-lit, night conditions. This difference appears to be unrelated to differences in the main- or side-road flow and in the main-road speed distribution, or to delay. The only known previous study of day and night gap acceptances at a similar junction by Tsungos and Weiner (1969) considered both crossing and merging and did not consider the street-lit case. Although that study produced different results, no significant differences were found for gaps between four and nine sec. For the merging maneuver, very few accepted gaps of less than four sec. were observed, none at night. The present study found that nearly 30% of the night data fall in this class, which may indicate a real difference in merging gap acceptance behavior between the populations. The main difference found in this study is that (for a closely constant population of side-road drivers), drivers appear to accept appreciably shorter gaps in darkness; a developed simulation model predicts that they thereby have a much higher risk of being involved in a serious accident. Interviews of a small sample of side-road drivers showed that they uniformly thought that they had exercised more caution in decision making during nighttime conditions. This suggests that they overestimate the time gaps available at night. The twilight data are consistent with the hypothesis that the observed difference between day and night gap acceptance is primarily due to the change in background light intensity, and not directly to the use of headlights.

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  • Supplemental Notes:
    • Sponsored in part by Transport and Road Research Laboratory.
  • Corporate Authors:

    Printerhall Limited

    29 Newmart Street
    London W1P 3PE,   England 
  • Authors:
    • Darzentas, J
    • Holms, V
    • McDowell, MRC
  • Publication Date: 1980-4

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Subject/Index Terms

Filing Info

  • Accession Number: 00386126
  • Record Type: Publication
  • Source Agency: National Highway Traffic Safety Administration
  • Report/Paper Numbers: HS-029 170
  • Files: HSL, USDOT
  • Created Date: Jun 28 1984 12:00AM