For those looking to find strong Transportation stocks, it is prudent to search for companies in the group that are outperforming their peers. Has Delta Air Lines (DAL) been one of those stocks this year? Let's take a closer look at the stock's year-to-date performance to find out.Delta Air Lines is a member of our Transportation group, which includes 156 different companies and currently sits at #11 in the Zacks Sector Rank. The Zacks Sector Rank gauges the strength of our 16 individual sector groups by measuring the average Zacks Rank of the individual stocks within the groups.The Zacks Rank is a proven model that highlights a variety of stocks with the right characteristics to outperform the market over the next one to three months. The system emphasizes earnings estimate revisions and favors companies with improving earnings outlooks. DAL is currently sporting a Zacks Rank of #2 (Buy).The Zacks Consensus Estimate for DAL's full-year earnings has moved 5.48% higher within the past quarter. This signals that analyst sentiment is improving and the stock's earnings outlook is more positive.According to our latest data, DAL has moved about 18.98% on a year-to-date basis. Meanwhile, the Transportation sector has returned an average of 15.95% on a year-to-date basis. This means that Delta Air Lines is outperforming the sector as a whole this year.To break things down more, DAL belongs to the Transportation - Airline industry, a group that includes 28 individual companies and currently sits at #47 in the Zacks Industry Rank. On average, stocks in this group have gained 8.29% this year, meaning that DAL is performing better in terms of year-to-date returns.Investors with an interest in Transportation stocks should continue to track DAL. The stock will be looking to continue its solid performance.Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report Delta Air Lines, Inc. (DAL): Free Stock Analysis Report To read this article on Zacks.com click here.