In what circumstances will the Crown not have to prove that the road was slippery, or that visibility was poor or slippery?

In R v. Watts [2007] O.J. No. 1382, the defendant rear-ended a bus. There was evidence of a strong smell of alcohol on his breath and that the defendant told a tow truck driver that he had had too much to drink and blacked out. The court found that the constellation of these factors including that there was no evidence that the road was slippery, or that visibility was poor, was enough for the crown to overcome its burden of proof.

In R v. Hackman [2016] O.J. No. 4434, another case of a rear-end collision, the indicia displayed by the defendant included that he smelled of alcohol, stumbled over his feet and appeared at one time slumped over and non-responsive. There was also evidence that the defendant told a civilian at the scene that he had failed to negotiate a lane change, consistent with a finding of undue care and attention on his part.