The transportations sector is made up of stocks that move customers or goods. Companies in this sector include air freight and logistics, trucking, road and rail. These companies make up the backbone of the economy.
Since so much of these companies expenses are fuel related, their value is very sensitive to the price of oil and gas and the products that go into producing it.
The transportation sector is considered a leading indicator of the economy and overall stock market direction. The theory being, the more goods being transported, the more economic activity is being created.