The trucker, apparently unable to reach a satisfactory climax, then proceeded to continue to pleasure himself during a police interrogation, the Borås Tidning newspaper reported on Thursday.
"He was masturbating while the police questioned him," police prosecutor Åsa Askenbäck told the newspaper.
"He has admitted that he was not paying full attention at the time of the accident. He was playing with himself instead of focusing on the road."
The truck driver was en route from Gothenburg to Borås at around 4 am on Tuesday morning. The truck and trailer flipped over when he rammed his vehicle into the central division on route 40 south of Borås.
The upturned vehicle blocked all traffic towards Gothenburg and one lane was closed in the direction of Borås.
The man remained in the vehicle with his hands apparently still clasped around his own gear stick and was subsequently arrested for reckless driving and driving while under the influence of drugs.
The suspicions against the man have now been extended to sexual molestation.
The German trucker, who is in his thirties, has admitted all of the charges directed against him.
Tidningarnas Telegrambyrå/The Local