Letterkenny Roads Policing Unit detected a vehicle travelling in excess of 80KPH in the confines of the town and within a 50KPH zone yesterday.
The vehicle was stopped and the driver was then arrested on suspicion of drug driving.
The motorist failed a drug driving test.
Court proceedings will follow.
“Do not take risks on the roads. Slow down and never drive while under the influence of drugs/alcohol,” a spokesperson for Letterkenny Garda Station said.