The flowers had now been removed and Ms Gibb has been asked "to take any further memorial to private land".
"It is clear that these areas are not designated for this purpose," Mrs Arnott wrote.
The mayor did not oppose the initial memorialising of the site, but said "grieving is a personal issue" and there was a time when the focus had to change.
A memorial on private land would be easier for the families to control, she said.
Ms Gibb didn't want the profile which had developed over the past week, nor the way the memorial had grown, but she hoped it prompted council into thinking about clear policy.
She believed such memorials served as reminders of the care needed on roads.
Brief inquiries by Hawke's Bay Today revealed there are other councils which also have no specific policy.
Hastings District Council has seen a proliferation of crosses marking tragedies on its rural roads and highways but has no specific policy that deals with flowers placed on poles at crash sites, either in urban or rural areas.
A council spokesperson said crosses at rural fatal crash sites had to conform to rules governing placement, style and quality.
Generally only one is allowed at each site, and the "construction" should be able to withstand the elements for at least five years.
Palmerston North also has no specific policy, but Councillor Adrian Broad said the Council had allowed people to put up a "couple" of "little" shrines which were managed in a sensitive way.
"They've been there for a while, but then the families have decided when it's time to take them away," he said.
Napier has at least three other long-standing roadside memorials, the most well-known being a tree on a Riverbend Rd reserve adorned with stuffed toys and other items almost every year since 3-year-old Teana Wereta Lange died there in December 1999 after the vehicle in which she was a passenger crashed.
With the tree having been torched and vandalised, the Council tried to have the memorial removed in 2008, but it remains in place, dominated by soft toys.
A plaque and tree on a grass verge outside the Maraenui service station in Bledisloe Rd commemorates the death of 18-year-old staff member Candis Dymock who was hit by a vehicle in September 1997, and plastic flowers on a railway crossing pole in Prebensen Dr are in memory of Bryan James Harvey, 26, killed as the car he was driving hit a railway wagon in October 2008.
Like other highways throughout the country, Hawke's Bay's are lined with crosses representing fatal crashes over the years.
The most notable memorial was a sculpture which stood over 2 metres tall near Takapau, where six people died in a head-on crash on Christmas Eve 1992.
It stood for more than 15 years.