More than 50 people have been arrested in the first two weeks of a Leicestershire Police anti drink-drive campaign.
Officers said 53 drivers had been arrested, with five testing positive for excess alcohol the day after they had been drinking.
Ch Insp Steve Potter said he was surprised by the number of people arrested the morning after.
He said people were unaware of how long alcohol takes to leave the system.
"People still think one drink is OK," said Ch Insp Potter.
"The legal limit of 35mg [of alcohol] per 100ml [of breath] cannot and should not be calculated by guessing because every person's body and tolerance to alcohol is different.
"Driving with any impairment whatsoever is dangerous," he said.
Officers made 17 arrests for driving under the influence of alcohol last Saturday and Sunday.
John Budulis, a road safety officer from Leicestershire Police, said the force had highlighted a real problem with people still being over the limit the morning after a night out.
"For the last two to three years we have been keeping a record of when we have been arresting people. One of the most popular times is between 0800 and 1200 GMT.
"The body only eliminates one unit of alcohol every hour, that's equivalent to half a pint of beer. So if you've had five or six pints the night before, yes you might have arranged transport home but you can still be over the limit the following morning."