The basics

The proposal is to raise the state sales tax from 5.6 cents to 6.6 cents for thirty years. Somehow this comes out to $42.6 Billion.

• This is an 18% tax increase.
• Sales taxes in Arizona cities would be among the highest in the nation. (for example, the rate in Phoenix would be 9.3%, Tucson 9.1%).
• Governor Napolitano, who backs the proposal, states that sales tax is the "only possible" means to pay for these monies.
• There is no sales tax on fuel (gasoline or diesel), presently or proposed.

The projects:

The vast majority, some 78%, would be earmarked for building roads.
A small portion would be devoted to public transportation projects -- mostly a rail line between Phoenix and Tucson.

sources:
Arizonans to get preview of $42 billion transportation tax plan Arizona Republic, May 4, 2008