5. Primary party rate
   The possibility of being the primary party (primary party rate) is shown in Fig. 11 in a collision with a four-wheeled vehicle only, for the reason explained in the previous section. Of the two parties directly involved in a traffic accident, the more negligent one is called the primary party and the other one the secondary party.

  Primary party rate = Number of primary parties / Number of primary + secondary parties × 100 (%)

  A higher primary party rate means a higher possibility of committing a violation. As can be seen in Fig. 11, with the age group around 35-39 at the bottom, the rate becomes higher for younger and older age groups in a U-shape in every accident year, apparently along with the effects of aging. For elderly drivers, however, the rate drops, although only slightly, in more recent accident years.

Fig. 11: Primary party rate for primary parties driving standard- and mini-sized passenger cars by age group (colliding with a four-wheeled vehicle)


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Institute for Traffic Accident Research and Data Analysis (ITARDA)