"He honestly believes that he did all the could in the circumstances," she said.
"He has been haunted by this incident and will continue to be for the rest of his days."
However, Judge David Mathers said he could have done more to prevent hitting Mr Wiltshier.
"You delayed for one or two seconds before you took all the appropriate steps [to avoid hitting the victim] and it was that delay which I found was the careless element in your driving.
"My finding was that if you had reacted as extensively as you could have, by braking earlier, then you would have stopped within a metre or so of having stuck him," he said.
Sommerville was sentenced to six months' loss of licence. He was also ordered to complete a defensive driving course and attend a restorative justice conference with Mr Wiltshier's partner and her daughter.
He had voluntarily refrained from driving for the past month, so his limited licence, allowing him to drive for work, could start immediately.
Sommerville said outside court he was looking forward to meeting the family for closure.
"I am nervous but it will be good to speak to them. This is something I have to live with for the rest of my life and so will they," he said.