As motorists heading into the Wiltshire town on the A419 from Oxford fretted at the back of an up to 12 mile-long tailback, those at the front were being waved into a census point manned by Swindon council and highways agency officers.
When Elaine Lippett, from Hungerford, was pulled over, all the surveyors asked her was her postcode and her destination.
"These people were taking in a few cars at a time, causing a lot of disruption," she said. "It must have wasted half an hour - it was ridiculous."
Swindon council, which carried out the census with the permission of Wiltshire police, said the survey, which lasted for 12 hours from 7am, was the last of 18 to be carried out at different points on routes into the town.
The aim of the programme was to develop a computer model to show how all modes of transport could ease congestion.
"We wanted to find out where people were coming from, where they were going and the purpose of their journey," said council spokeswoman Helen Barnes. "There was a hold-up but our engineers didn't think it was bad enough to stop the census."