Motorists impatient with cyclists should watch out for a ghostly spectre as they drive past the scene of a fatal bike crash on Auckland's Tamaki Drive.

Chained to a post across the road from where pedalling British nurse Jane Bishop was killed by a truck in November as she swerved to avoid an opening car door is a large white bike which appears to have popped up out of nowhere several weeks ago.

But although there is nothing on it to state its purpose or to indicate who put it there, it seems part of an international movement to commemorate fallen cyclists with "ghost bikes" to keep silent watch over where they died.

Cycle Action Auckland deputy chairwoman Barbara Cuthbert, a campaigner for safety improvements on Tamaki Drive, said yesterday she admired whoever provided the bike but had no idea of that person's identity.

"A ghost bike just turns up - it represents the ghost-rider of the person killed there," she said.

"Yes, it is somewhat macabre but at the same time I think it's a very reasonable reminder of an event we never want to see repeated on Tamaki Drive."

According to the website, the idea of providing "small and sombre" memorials to dead pedallers began in St Louis, Missouri, in 2003 and has spread to more than 100 places throughout the world.

"They serve as reminders of the tragedy that took place on an otherwise anonymous street corner and a quiet statement in support of cyclists' right to safe travel," says the website, which is hosted by the New York City Street Memorial Project.

"We hope to create a space where those lost on dangerous streets can be remembered by their loved ones, members of their local communities and others from around the world. We also hope to inspire more people to start installing ghost bikes in their communities and to initiate changes that will make us all safer on the streets."

Although the Tamaki Drive apparition has yet to appear on the website's global register, two ghost bikes provided at fatal crash sites near Whangarei by keen cyclist and shop worker Ryan Branson are listed on it.

Mr Branson, who was unaware of but pleased to be told about the Auckland memorial, painted an old bike to put beside the road at Maungatapere to mark the death of road safety campaigner Fred Ogle at the hands of a hit-and-run driver in August 2008.

The following month, he found himself getting out his paintpot again after travel agent and athlete Lynley McDonald was knocked off her bike and killed while riding with her father along Pipiwai Rd, northwest of Whangarei.

Mr Branson has also dedicated a third machine to the cause, after his first memorial to Mr Ogle was vandalised soon after its installation, but says both ghost bikes have since become accepted parts of the Northland landscape.

"They are like the white crosses you get for people in cars, or pedestrians," he said.

"When you think of the time involved in getting an old bike and painting it, it's worth it in the end as a bit of awareness."

Mr Branson said Auckland drivers did not have a monopoly on failing to keep 1.5m away from cyclists when passing them.

"It doesn't seem to be working with some people up here [in Northland]," he said.

"I notice a lot of logging trucks and large commercial vehicles giving us more attention by giving us a wider berth, but a lot of cars are getting pretty close."