title: Time-to-collision judgments under realistic driving conditions.
abstract: OBJECTIVE
  This study examined perceived time to collision (TTC) with automobile drivers under realistic approach, rear-end crash scenario conditions.
  
  
  BACKGROUND
  TTC refers to the time before impact if prevailing conditions continue.
  
  
  METHODS
  In this test track study involving 51 drivers ranging from 20 to 70 years old, the driver's vision was occluded at either 3.6 or 5.6 s TTC during an in-lane approach to a lead vehicle. Drivers provided TTC estimates by pressing a button the instant they felt that they would have collided with the vehicle ahead.
  
  
  RESULTS
  Results indicated that TTC was consistently underestimated. The TTC ratio (perceived TTC/actual TTC) increased as driver speed decreased and as relative speed increased. These ratios were largely unaffected by age, gender, actual TTC, viewing time (1 s vs. continuous), and the presence of an eyes-forward, mental addition distraction task.
  
  
  CONCLUSIONS
  Overall, these results suggest that under these low TTC conditions drivers estimate TTC in a relatively uniform fashion and that they are capable of providing this estimate based on a brief glimpse to the vehicle ahead.
  
  
  CONCLUSIONS
  These results are being used to develop an alert timing approach for a forward collision warning system intended to assist drivers in avoiding rear-end crashes with the vehicle ahead.
authors.affiliation: General Motors Structure and Safety Integration Center, 30200 Mound Rd., Mail Code 480-111-E18, Warren, MI 48090-9010, USA. raymond.j.kiefer@gm.com
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Kiefer
authors.forename: Carol A
authors.initials: CA
authors.lastname: Flannagan
authors.forename: Christian J
authors.initials: CJ
authors.lastname: Jerome
mesh_terms: D000063:Accidents, Traffic; D000328:Adult; D000368:Aged; D001334:Automobile Driving; D005260:Female; D005431:Florida; D006801:Humans; D007600:Judgment; D008297:Male; D008875:Middle Aged