A new sales tax exemption that encourages Washington car shoppers to choose hybrids and alternative-fuel vehicles will save them an estimated $18.6 million over the next two years.

The savings provide an extra incentive for consumers to trade in gas guzzlers, a trend that's already in full bloom.

"It's probably not going to make that big of an impact on hybrid sales in Washington," said Bill Soholt, general sales manager of Toyota and Honda of Seattle.