Salt and sugar make ice melt equally as fast as each other. Sugar, alcohol, salt varieties and other foreign substances all help ice melt faster because they lower the freezing point of the ice.
The most commonly used substance to help make ice melt is salt because it is the only substance that works well and is inexpensive. The salt that is used works equally as well as other substances, but it is cheaper. In some instances, sand and cinder materials are also used to help make the ice melt.
Nearly any substance that is not water will help make ice melt more quickly. Molecules of foreign substances can help depress the freezing point. Each mole of a foreign substance that is added to ice will lower the freezing temperature by around 1.7 to 1.9 degrees Fahrenheit. The freezing point is reduced because the molecules are less concentrated in a mixture of water and something else, such as salt or sugar, than they are in pure water. The lower density of molecules does not allow the freezing process to occur as quickly and will help to reduce any freezing that has already occurred.
Salt is not able to keep water from freezing indefinitely. When the salt reaches a temperature of around -21 F, it will begin to stop working with the water to prevent freezing. It will crystallize and create an ice like solution as if the salt was not there at all.