Attention is perhaps the limiting factor, but being able to look in two directions at once would help, and would help greatly if we had more attention capacity. E.g. anytime you change lanes you have to alternate between looking behind, beside, and in front and that greatly reduces reaction time should something unexpected happen in the direction you aren't currently looking...

Humans have both issues. There are many human failures which are distinctly a vision issue and not attention related, e.g. misestimation of depth/speed, obscured or obstructed vision, optical focus issues, insufficient contrast or exposure, etc.