Kim et al. (2002) analysed motorcycle crashes in the US state of Hawaii between 1986 and 1995 and found that 40% of motorcycle crashes on the island were single vehicle crashes. Whilst this study included all road types, crash clusters appeared to be focused around urban areas. Single vehicle collisions were over-represented in serious injury crashes, on curved roads, roads with defects, and roads that were wet, oily, or otherwise contaminated. Riders who were speeding or alcohol impaired at the time were also over-represented in single vehicle motorcycle crashes.