We conducted our own drink-driving research at Britain's Transport Research Laboratory (TRL), using one of the world's most advanced driving simulators, and the simple answer is that it's impossible to tell.
Our four volunteers practiced using the simulator before having key safety aspects of their driving assessed while driving a 10-minute preset route with random traffic conditions.
Then they were asked to drink alcohol (vodka with a mixer) until breath tests confirmed they had 50mg/100ml of alcohol in their blood (the legal limit in most European countries).
They were assessed again while driving along the same route. All were surprised how tipsy they felt with 50mg/100ml of alcohol in their blood. Finally, they drank more alcohol and were assessed at the current UK drink-drive limit of 80mg/100ml.
Height 5ft 5
At 80mg/100ml, Anna had gone beyond initial light-headedness and had started to feel drowsy. 'I could tell my responses were slower, and even though I was trying hard to drive properly, my concentration just wasn't there,' she said.
Height 5ft 7
Rob, who needed to drink more than the other volunteers (a frightening 12 shots) to get to the legal limit, said: 'It's mad that I could legally drive my car home now. No person in their right mind would drive after drinking this much, so why does the law say it's okay?'
Height 5ft 8
Oliver said: 'I wouldn't dream of driving feeling the way I did after a drink, and I hadn't had an awful lot. At a pub you don't notice getting drunk, but in this test environment you can really notice the effects of the alcohol.'
James said: 'I can certainly tell I've been drinking, and I felt myself having to concentrate harder in the simulator than when I was sober.'