XTN offers a straightforward work-around for the transportation industry's high concentration by equal-weighting its holdings. That drastically cuts its weighted average market cap and introduces some sector biases. Eligible securities must be included in the S&P Total Market Index and must meet certain liquidity and capitalization thresholds. The Underlying Index includes the following sub-industries, as defined by GICS: air freight & logistics, airlines, airport services, highways & rail tracks, marine, marine ports & services, railroads, and trucking. The index undergoes quarterly rebalance.