Les O'Donovan, the grandfather of Pahiatua teen Kane Thomas O'Donovan - who was killed in 2013 when his car veered off the road - said safety barriers may have prevented the car from going into a ditch.
The 17-year-old had been on the way to visit his grandparents in Featherston when he lost control on a twisty, downhill part of the road, Mr O'Donovan said.
"I've driven up that way lots, and that wider part is beautiful to drive, but that other bit is quite a contrast, so I think [improvements] would make a big difference.
"And if it was straightened out it would certainly make a big difference."
All it took was a second's inattention, Mr O'Donovan said.
"It doesn't take much, and the young ones think they are better drivers than they are."
Almost three years after the crash, he still thinks about his grandson every day.
"I still haven't really got over it, to be honest. It's just the young age ... the thing that really gets you is he had the potential to make a really good person. A lot of kids moan or grizzle, but he just would go and do things. He was awesome.
"He'd make a cup of tea or do the dishes, you didn't have to force him, he just did it. It was a real sad loss."
Wairarapa Road Safety Council manager Bruce Pauling said any roading or structural improvements were a "great thing for Wairarapa".
"We welcome, absolutely welcome, any improvement that's going to stop deaths and serious injuries.
"If you're talking safety on roads, there's a number of elements; there's safe vehicles, safe roads and roadsides, safe speeds, and safe user behaviour.
"This is obviously a large investment in one of those cornerstones.
"Anything we can do to improve the safety of anybody travelling through Wairarapa, we welcome."
The investigation into the Mt Bruce and Rimutaka Hill improvements is expected to begin either this year or next, with work due to start on the Carterton to Masterton improvements in mid-2017.
