A leading wheelchair racer crashed and several pulled out of Sunday's World Championship marathon in New Zealand because roads were open to traffic.
Britons David Weir and Shelly Woods opted out and some team officials were forced to act as traffic marshals.
"I just thought it was ludicrous. I didn't want to risk getting injured or getting run over," said Weir.
It marred the end of a successful championships for Great Britain, who finished third overall with 38 medals.
GB head coach Peter Eriksson said the racers "felt it was too dangerous" and the team supported their decision.
France's Denis Lemeunier crashed but received only minor injuries.
Eventual winner Kurt Fearnley of Australia said: "It's a real shame.
Safety is paramount, and with less than 600 days to go the London 2012 Paralympics this presents a danger we are not prepared to take.
GB head coach Peter Eriksson
"To see on the start line, friend after friend pull out is not the way you want to start a race. "
Londoner Weir, 31, was denied the chance to go for a fourth title, having earlier
on the track in the T54 800m, 1500m and 5000m events.
The 24-year-old Woods, a 2007 London Marathon winner, had also
won World bronze
in the 5000m.
Both athletes came to the warm-up area for the start of Sunday's race but Eriksson said that, after lengthy discussions, they decided not to compete.
"According to IAAF rules, under which this event is governed, there has to be complete road closures," he said.
"Our athletes can be peaking at speeds of 40-50km an hour and due to their low racing positions, visibility is poor for passing traffic.
"After a hugely successful World Championships overall for the team, we fully support their decision, although obviously the athletes and UK Athletics as a whole are disappointed that they can't show what great form they're in.
"Safety, however, is paramount, and with less than 600 days to go the London 2012 Paralympics this presents a danger we are not prepared to take."
In a statement, the International Paralympic Committee blamed local organisers and pledged to investigate further.
"It is the local organising committee's responsibility to ensure safety and organise the marathon," the statement read.
"Safety is our first priority. It is understandable the Canadians and the British withdrew and we are launching a full investigation."
Overall, though, GB coach Eriksson was pleased with a championship medal haul of 38 that easily surpassed that from previous events in Assen in 2006 (27) and Lille in 2002.
Only China and Russia finished higher in the overall standings and only China secured more medals in total, with 58.
"The most important benchmark for us coming into this was our 18th place team finish in the Beijing Paralympic Games two years ago," said Eriksson.
"We came out here knowing that a top 10 finish in the medal table would be a step in the right direction.
"And having finished third on the medal table behind two of the world's leading nations in Paralympic track and field, I'm absolutely delighted.
"Our more experienced athletes have, in the main, continued to deliver medals at the highest level while our junior athletes have proved that while Rio 2016 may be their realistic target, London 2012 is very much a possibility, and a podium one at that."
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