A bleak picture of lengthy road closures and queuing traffic was painted to businesses at a Craven meeting to discuss the Tour de France.
Highways and emergency planning officers from North Yorkshire County Council said they wanted people to be in no doubt of the scale of the event, which will pass through much of Craven during the first weekend of July.
Many thousands of people are expected to camp across Craven.
It was the equivalent of putting the population of Keighley up on the moors, the meeting in Skipton Town Hall heard.
Skipton High Street will be closed to additional spectators if numbers exceeded health and safety limits of 11,000 and travelling around the area is expected to be difficult on both days leading up to the event and in the days afterwards.
Tom Bryant, from the county council, said the local authority had wanted residents and businesses to be clear of the size of the event so they could be well prepared.
“We are expecting up to a million people across the two stages, which is simply unprecedented in North Yorkshire and a real challenge for us,” he added.
About 80 per cent of temporary car parking was on grass and was dependent on fine weather, which meant alternatives would have to be found. He said the closure of roads along the route would be for an “absolute minimum” of eight hours and stressed much time was needed to make sure the routes were race fit.
“We don’t want to become renowned as the place where the Tour de France got stuck because traffic management did not work,” he said.
Inspector Will Scarlett said officers would work 12-hour shifts, be stationed around the district and work closely with other emergency services.
“It is going to be hard but we are going to try to deliver a normal service. There will be massive pressure on us and we will have to prioritise,” he added.
But despite being told Craven faced an event of “unprecedented scale”, it was a fantastic opportunity with benefits for many years to come.
Sharon Hudson, of Craven District Council, said a massive amount of work was under way to make sure it passed as smoothly as possible but said shops and businesses were unlikely to do a roaring trade on the Saturday as, once in place, spectators were unlikely to want to move.
The Grand Depart makes its way through Craven on July 5 and then through Silsden, Keighley and the Worth Valley the following day.