The study by the National Roads Authority also reveals “worryingly low” rates of back seat passengers wearing seat belts, with less than half of all adults doing so.
The report, Free Speeds (Urban and Rural) and Seat Belt Wearing Rates - 2003, which was published yesterday shows that good progress has been made in seat belt compliance levels among front-seat passengers.
Speed surveys conducted by the NRA have also highlighted significant reductions in the number of cars breaking speed limits on dual carriageways, national primary routes and in urban residential roads.
Better compliance rates have been recorded for most category of roads since similar surveys were held in 2002.
The most dramatic improvement came in observance of speed limits in built-up areas, with 64% of drivers keeping below the 30mph standard limit in 2003 compared to just 39% in the previous year.
The number of drivers exceeding the speed limit on dual carriageways fell from 43% in 2002 to 29% last year.
Average car speeds are 66mph on motorways, 57mph on dual carriageways, 58mph on national primary roads and 28mph in built-up areas.
However, the NRA said there was significant scope for further improvements in the observance of speed limits, particularly by the drivers of goods vehicles.
The number of heavy goods vehicles which break the speed limit on motorways rose from 81% to 85% last year, with average speeds of 53mph. (The speed limit for HGVs on motorways is 50mph compared to 70mph for cars.)
The NRA said the results of the survey, conducted in the second half of 2003, were “undoubtedly influenced” by the introduction of penalty points.