Underlying Asset Performance: The performance of the constituent companies within the iShares Transportation Average ETF (IRTR.US) significantly impacts its price. Positive earnings or growth in these transportation firms typically drive up the ETF's value.

Market Sentiment: Overall investor mood regarding the transportation sector or the broader market can heavily influence IRTR.US's price, leading to buying or selling pressure.

Economic Conditions: Economic indicators like GDP growth, consumer spending, and freight volumes directly affect transportation demand and thus, impact the ETF's performance.

Interest Rates: Changes in interest rates affect the cost of capital for transportation companies, influencing their profitability and impacting the ETF price.

Supply Chain Dynamics: Disruptions or improvements in supply chains affect the movement of goods, impacting transportation companies and, subsequently, the ETF price.

Fuel Prices: Transportation companies' profitability is affected by fluctuations in fuel prices, which in turn, affects the ETF price.