Up to 55% of drivers in Wales admit to speeding on most days, according to a report published by the RAC.
The RAC says speeding drivers need 'the harshest penalties'
The research claims the number of drivers speeding regularly is up almost 10% on a year ago.
It said that overall 57% of drivers broke the motorway speed limit, and almost two-thirds exceed 30mph speed limits.
The figures came as another survey showed Wales had one in eight of the UK's mobile speed camera sites.
The 2005 RAC Report on Motoring published on Monday suggested current enforcement of speeding restrictions appeared to have little impact.
The most common reason given for speeding by those surveyed was the small chance of being caught. The RAC has termed this "driving under the radar".
RAC spokesman Philip Hale said: "In Wales we have something of a speeding epidemic on our hands.
Wales has one in eight of all mobile speed camera sites
"More motorists than ever are admitting to disorder on the roads. Overall, 16%, or four million British drivers, do not consider themselves law-abiding, almost double last year's figure.
"Enough people to fill 10 commercial holiday jets die every year on Britain's roads.
"Individual motorists know these risks, yet choose to ignore them - drivers are speeding undeterred on all types of road, at all times of day, every day of the week and would only respond to the harshest penalties."
The RAC said better detection, penalties and education were necessary to cut the number of speeding drivers.
It recommended the introduction of graduated speeding penalties so that worst offenders would receive the harshest punishments, as well as mandatory driver re-training and education after a speeding ban.
Meanwhile, the number of mobile road safety camera sites in operation in the UK rose by 34.5% during 2004, according to Cyclops, a company which manufactures detectors warning drivers about camera locations.
It said Wales had 12.6% of the sites, or one in eight.
The largest concentration of mobile sites, those patrolled by radar or laser operated speed cameras, were in south-east England, with 17.6% of the UK total.
The lowest numbers were in Scotland, with 8.7%.