Transport analyst Matt Lowrie told Newstalk ZB it was clear the cities had the new buses, while the old ones were on-sold cheaply to the towns.
"I've been on some of those buses before and, yeah, sometimes you wonder why they are still on the road and I guess some of that is a cost issue and is that appropriate?
"I wouldn't think so.
"I can't speak for the specific examples that have occurred because I don't know the details of them but we do seem to have a lot of older buses particularly out in the regions.
"We may need to be looking at that.
"I think the public want to know that their buses are safe... that they can use them safely without fearing for their lives."
Lowrie said urban buses were generally much safer.
"There's stricter requirements around them. In Auckland and Wellington in particular, they have been replacing [buses] recently so a lot of the fleets are quite young."
However, he said this was clearly not always the case outside the major city centres.
"I've been on some of these buses before and you do sort of wonder why they are still on the road."
This morning, Ngāi Te Rangi Iwi Trust chief executive Paora Stanley defended the safety record of the bus involved in the Sanson crash.
"The bus had a thorough examination and passed its COF [Certificate of Fitness] within the past three weeks.
"The model is known to be a very reliable model. The drivers are experienced drivers."
The bus was owned by Ngāi Te Rangi, he said, and had been regularly taken cross-country journeys.
"In any incident like this, the police carry out a thorough investigation. Let's avoid all speculation and wait for the result of the standard police investigation."
Stanley commended the police for their handling of the aftermath of the crash, saying they were "absolutely outstanding".
The police Commercial Vehicle Safety Team was investigating the causes of the two crashes.
