Furious Welsh locals have warned that drivers could get distracted by checking their speedometers instead of looking at the road ahead when Mark Drakeford's blanket ULEZ-style 20mph speed limit comes into effect.
The new go-slow restrictions start on Sunday but drivers are already clogging up urban roads by 'tootling along' at under 20mph.
Businesses fear it will hit their trade as badly needed tourists will stay away from Wales for fear of an unwanted souvenir - three points on their license.
Some drivers believe it's a money-making exercise by the Welsh Government whose first minister Mark Drakeford is under fire by introducing the new legislation.
A staggering £32.5m is being spent on the new signs, money which taxpayers say should have gone to the NHS.
But the Welsh Government insists that the 20mph speed limit will result in 40 per cent fewer collisions each year and up to 10 lives will be saved.
A glossy bi-lingual leaflet delivered to every home in Wales says: 'Most journeys will be around one minute longer'.
Catering boss Jamie O'Leary, 42, said: 'I don't believe their figures - most journeys will be a lot longer.
'You have to factor in that some drivers will go below the speed limit because they don't want to get caught.
'This will seriously affect supply chains coming into Wales. Delivery drivers aren't going to want to come here if it's going to add a third onto their journeys.
'And tourists won't come to Wales if they fear a £100 fine and three points on their licence. They will have to change their mindset every time they cross the Severn Bridge.
'Most people in Wales think Mark Drakeford's got this wrong - he doesn't even drive a car these days.
'It's hard to drive at 20mph, the car doesn't know whether to go up to third gear or labour in second.'
The Welsh Government leaflet advises drivers: 'When you see streetlights assume the speed limit is 20mph unless you see signs that say otherwise.'
But Rob Williams, 54, of Treherbert, Rhondda, said: 'That's going to clog up every street, every morning and evening in every town and village in Wales.
'It will lead to more crashes because drivers will be going along checking their speedos and not looking at the road in front of them.
'People on the school run on Monday should be prepared for drivers running into the back of them.
'If you ask me it's a money-making exercise and they're turning Wales into snails.'
The new law was blasted as 'ridiculous' by customers at the roadside West End Cafe in Llandovery, Carmarthenshire, a favourite with leather-clad bikers.
Barney John, of Neath, South Wales, said: 'The A470 which connects North and South Wales is 60mph outside Newbridge-on-Wye then it goes down to 20mph for 500 yards. It's ridiculous.
'Part of their argument is emissions but my car runs more efficiently at 50mph than at 20.'