Research Papers

Determination of Snowmobile Deceleration Rates for Ejected Occupant Scenarios

Filename cmrsc19_32.pdf
Filesize 251 KB
Version 1
Date added June 7, 2009
Downloaded 4 times/fois
Category 2009–CMRSC-XIX–Saskatoon
Tags Session 1A
Author/Auteur Jason A. Young, Michael T. Sinnott

Abstract

In collision reconstruction, skid distances are a reliable tool in helping to determine the pre-impact speed of a vehicle. When reconstructing a snowmobile accident, the ‘skid-to-stop’ distance of the snowmobile can similarly be used to help determine the impact speed, if the deceleration rate of the snowmobile is known. For some basic scenarios, snowmobile deceleration rates can be estimated from the literature. However, for scenarios where the snowmobile rider is ejected during impact, which is often the case (as with motorcycle or bicycle collisions), the ‘coasting’ deceleration rate of the unoccupied snowmobile is required. To our knowledge, this coasting deceleration rate for unoccupied snowmobiles has not been previously documented. In motorcycle or bicycle collisions, the vehicle will typically fall over and a sliding coefficient of friction can be used. However, an unoccupied snowmobile can continue gliding upright if its rider is ejected. In such cases, the snowmobile suspension would be expected to ‘unload’ the weight on the high-traction belt that drives the snowmobile, leaving more weight on the low-friction front skis. In this initial study using a live test subject, the deceleration of a moving snowmobile was measured when the occupant was suddenly ‘thrown’ from the vehicle and the snowmobile was allowed to coast to a stop. Safety measures were taken to ensure that the tests could be conducted safely. Starting speeds of up to 40 km/h were tested, both on fresh powder snow and on pre-made snowmobile tracks in powder. Control runs with no occupant ejection were also conducted at speeds of up to 90 km/h, allowing the snowmobile to coast to a stop (simulating an unconscious or stunned rider). For the ‘ejected occupant’ test runs, the average snowmobile coasting deceleration was 0.24 g, with 3 of the 4 test runs being 0.19 g (range of 0.19 g to 0.39 g; 1 ‘g’ = 9.81 m/s2). For the ‘unconscious occupant’ test runs, the average snowmobile coasting deceleration was 0.27 g (range of 0.14 g to 0.37 g). When the results were categorized by the test speeds, other trends emerged. In particular, the coasting deceleration increased with increased speed (0.19 g avg. [SD = 0.00 g] at 26 to 33 km/h, 0.25 g avg. [SD = 0.10 g] at 40 to 60 km/h, 0.35 g avg. [SD = 0.01 g] at 90 km/h). The results of this initial research study are hereby being made available to both the public and private sector reconstruction communities to assist in analyzing snowmobile accidents. Further research is recommended to gather additional data and to extend the ‘ejected’ scenario research to higher speeds. Further research is also recommended to extend the study to various brands of snowmobiles to check the sensitivity of the data to product features such as weight, centre of gravity and suspension design.

Jason A. Young, Michael T. Sinnott