http://www.wsdot.wa.gov/winter/research.htm
The issues surrounding studded tire performance and safety are complex. From the standpoint of traction alone, studded tires, when new, often provide some benefit over other tire types on ice-covered roads when the temperature is near freezing. However, the advent of the new studless tires has diminished the marginal benefit, and recent studies suggest that the infrequent, narrow range of conditions necessary for benefit from studded tires may not outweigh their detrimental effect on traction in dry or wet conditions on certain pavement types. In addition, a host of primary and secondary safety factors are related to studded tire use, many of which are very difficult to quantify, including facets of driver behavior and safety perception.
This study was conducted in cooperation with the U.S. Department of Transportation, Federal Highway Administration by Robert R. Scheibe in October 2002.
http://www.wsdot.wa.gov/winter/studtire/Studded_Tire_Report_Final_Nov_2002.pdf
http://www2.vti.se/nordic/3-03mapp/sunflower.html
The survey of tyre use in Östergötland county, southern Sweden, shows that the proportion of studded tyres increased from ca 75 per cent before the introduction of the Law to ca 80 per cent after its introduction. The proportion of winter tyres without studs increased from ca 15 to ca 20 per cent. The use of summer tyres was cut by half during the 1990s even before the requirement concerning winter tyres came into force, i.e. people expected the requirement and adjusted accordingly. The term ‘winter tyres’ in the Winter Tyre Law refers to winter tyres both with and without studs.
In the summer of 1999 the Swedish Government promulgated a Decree according to which cars, light lorries and buses, of a total weight not exceeding 3.5 tonnes, shall during the period 1 December–31 March, when travelling on a road, be fitted with winter tyres or similar equipment when winter road conditions prevail.
http://www.tieh.fi/winter.htm
In Finland the use of studded tires began in the early 1960's. Finland has been and still is the leading country in the use of studded tires. In wintertime 95 % of passenger cars have studded tires.