4.— (1) A person shall not drive or attempt to drive a mechanically propelled vehicle in a public place while he or she is under the influence of an intoxicant to such an extent as to be incapable of having proper control of the vehicle.

F8[(1A) Subject to subsection (1B), a person shall not drive or attempt to drive a mechanically propelled vehicle in a public place while there is present in his or her body a quantity of a drug specified in column (2) of the Schedule such that, within 3 hours after so driving or attempting to drive, the concentration of that drug in his or her blood is equal to or greater than the concentration specified in column (3) at the same reference number.

(1B) Subsection (1A) does not apply to a person in respect of a drug specified at reference number 1 or 2 in column (2) of the Schedule where the person is the holder of a certificate, in the prescribed form (referred to in this Part as a “medical exemption certificate”) which indicates that at the time at which that drug was found to be present in his or her blood Δ⁹ - Tetrahydrocannabinol had been lawfully prescribed for him or her and which is signed by the doctor who prescribed it.

(1C) A person who signs a medical exemption certificate containing information which he or she knows to be false commits an offence and is liable on summary conviction to a class C fine.]

(2) A person shall not drive or attempt to drive a mechanically propelled vehicle in a public place while there is present in his or her body a quantity of alcohol such that, within 3 hours after so driving or attempting to drive, the concentration of alcohol in his or her blood will exceed a concentration of—

(a) 50 milligrammes of alcohol per 100 millilitres of blood, or

(b) in case the person is a specified person, 20 milligrammes of alcohol per 100 millilitres of blood.

(3) A person shall not drive or attempt to drive a mechanically propelled vehicle in a public place while there is present in his or her body a quantity of alcohol such that, within 3 hours after so driving or attempting to drive, the concentration of alcohol in his or her urine will exceed a concentration of—

(a) 67 milligrammes of alcohol per 100 millilitres of urine, or

(b) in case the person is a specified person, 27 milligrammes of alcohol per 100 millilitres of urine.

(4) A person shall not drive or attempt to drive a mechanically propelled vehicle in a public place while there is present in his or her body a quantity of alcohol such that, within 3 hours after so driving or attempting to drive, the concentration of alcohol in his or her breath will exceed a concentration of—

(a) 22 microgrammes of alcohol per 100 millilitres of breath, or

(b) in case the person is a specified person, 9 microgrammes of alcohol per 100 millilitres of breath.

(5) A person who contravenes this section commits an offence and is liable on summary conviction to a fine not exceeding €5,000 or to imprisonment for a term not exceeding 6 months or to both.

(6) A person charged with an offence under this section may, in lieu of being found guilty of that offence, be found guilty of an offence under section 5.

(7) Section 1(1) of the Probation of Offenders Act 1907 does not apply to an offence under this section.

(8) A member of the Garda Síochána may arrest without warrant a person who in the member’s opinion is committing or has committed an offence under this section.