Due to the shame of suicide, medics usually won't label a death a suicide if any other cause of death is conceivably possible.
That's why it's believed that car crash suicides and pill suicides are undercounted.
Unfortunately, pill suicides have only about a 3% recorded success rate (although it's probably higher than that in reality since doctors will sometimes record successful pill suicides as accidental overdoses), and car crashes can endanger others, unless the road is completely empty.