The date for a new give-way rule change to come into force was pushed forward because of concern motorists would think it was an April Fools' joke.
The decision to change the date for dropping the give-way-to-the-right rule at intersections from April 1 to March 25 was revealed in a series of emails disclosed to Fairfax Media under the Official Information Act.
The emails, sent from August 17, showed Transport Minister Steven Joyce's private secretary Monique Waayer was concerned about whether April Fools' Day was the right day.
Senior adviser Paul Fistonich responded that April 1 had been widely reported as the date for the rule change, so motorists would know it was not a joke.
"From a [communications]-advertising perspective 1 April is better and much more memorable, even if there are negative connotations around that date," Mr Fistonich wrote.