The Effect of Microcars’ Lightness and Compactness on Safety in Side Impacts

In this paper, the term ‘microcar’ refers to a car which is categorized as L7 by the UN and conforms to the Ultra Compact Mobility regulation in Japan. The car is much lighter and smaller than a conventional passenger vehicle. It is generally understood that a microcar has poorer crash safety performance than a conventional passenger car. In particular, the microcar would seem to have a disadvantage in terms of side-crash protection performance, since a smaller gap between an occupant and the door means a shorter distance to absorb the impact energy. On the other hand, having a lighter mass, it moves earlier when struck, meaning that the speed and depth of the door intrusion is reduced: an advantage. Thus the severity of a microcar side crash is not obvious. The aim of this study is to find out how the lightness and compactness of the microcar affect its side-crash protection performance. This study was conducted using a numerical simulation of a Japanese K-car full-vehicle model. Two kinds of parameters were created. One is the Vehicle mass, the other is the Gap between the door inner panel and an occupant. Three levels of mass were investigated (351 kg, 658 kg, and 1000 kg) by removing parts which do not contribute to vehicle body strength or adding weight to the center of gravity. The UN R95 load case was selected for the evaluation. To simulate the microcar, the crash dummy and the seat were repositioned outboard laterally from the original position, the seatbelt was fastened without a pretensioner, and there was no airbag. The struck microcar’s velocity was obviously affected by its vehicle mass: the lighter the mass, the sooner the vehicle moved after the Moving Deformable Barrier (MDB) impact. However, the door velocity profile was almost the same in every vehicle mass condition up to the time of the peak injury value, so the injuries were at the same level—except for the head region, which was impacted by the roof rail. The lighter vehicle produced the higher head impact velocity, resulting in higher head injury values. As for the effect of door clearance, larger clearance seemed to reduce the injury level—slightly but demonstrably. This study indicated that the effect of vehicle mass (in the 358 kg–1000 kg range) on crash severity seems to be very small for the chest-to-pelvis region. On the other hand, the lighter vehicle mass seems to carry a higher injury risk for the head region. Thus it is suggested that the focus for microcars’ side-impact safety should be on protection performance for the head rather than the chest-to-pelvis area.


  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; Photos; References; Tables;
  • Pagination: 12p
  • Monograph Title: 27th International Technical Conference on the Enhanced Safety of Vehicles (ESV): Enhanced and Equitable Vehicle Safety for All: Toward the Next 50 Years

Subject/Index Terms

Filing Info

  • Accession Number: 01888610
  • Record Type: Publication
  • Report/Paper Numbers: Paper number 23-0027
  • Files: TRIS, ATRI, USDOT
  • Created Date: Jul 24 2023 4:38PM