The 74-year-old woman, the only occupant in her car, was flown to Palmerston North Hospital with "life threatening" injuries and was expected to remain there for several months, making a slow recovery.
Walker suffered only minor injuries to his right wrist and left hand and had admitted to police he was at fault, and had not seen the woman's car approaching the intersection.
Lawyer Jock Blathwayt said his client had been a postman for four years and was on the road six days a week.
"He can recall looking right and then looking left and not seeing anything before he entered the intersection," Mr Blathwayt said.
He said the woman driver may have been just before a nearby bridge at the very instant that Walker had looked left.
Mr Blathwayt said Walker was "mortified" at the crash.
He and the woman were neighbours and friends. Judge Bill Hastings acknowledged Walker was very sorry for the crash and the injuries it had caused.
"The victim doesn't remember anything. She says she doesn't feel angry and she knows you are upset."