THE EFFECT OF SIMPLIFYING ASSUMPTIONS ON MOMENTUM SPEED ESTIMATES

This technical report points out some of the fallacies in applying simplifying assumptions to a typical situation where two vehicles collide. This is when two cars approach a junction at which a traffic signal is inoperative, neither vehicle is braked, and the post-impact motions of the vehicles include rotation, skidding, and rollout to their final resting positions. Although this scenario is not uncommon, such crashes are often reconstructed by a linear momentum analysis, whose assumptions about post-impact parameters have little regard for vehicle dynamics or the laws of physics. Four of the many possible incorrectly treated factors are noted. The correct analysis of the accident data is much more demanding mathematically than linear momentum analysis, and it often cannot be completed due to lack of empirical data. The report demonstrates how very bad this simplified post-impact analysis is, when it was applied to several very well documented 'staged collisions'. It is easy to show that the technique of matching damage profiles to determine approach angles can sometimes produce very large errors in estimating impact speeds. In one example, changing the alignment of the vehicles by 7 degrees could change the estimated speed of one of the vehicles by as much as 22%.

  • Availability:
  • Corporate Authors:

    METROPOLITAN POLICE FORENSIC SCIENCES LABORATORY

    109 LAMBETH ROAD
    LONDON,   United Kingdom  SE1 7LP
  • Authors:
    • KWASNOSKI, J B
  • Publication Date: 1995

Language

  • English

Media Info

  • Features: References;
  • Pagination: p. 111-3
  • Serial:
    • IMPACT (ITA1)
    • Volume: 4
    • Issue Number: 4
    • Publisher: METROPOLITAN POLICE FORENSIC SCIENCES LABORATORY
    • ISSN: 0959-4302

Subject/Index Terms

Filing Info

  • Accession Number: 00722428
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD
  • Created Date: Jun 28 1996 12:00AM