As the stock market readies to close out an uncharacteristically strong September, the Dow Jones Transportation Average jumped to its third record high in as many days, gaining 0.47% to 9,886.32 on Thursday, Sept. 28.

Thursday's fresh high comes after new records set on Tuesday and Wednesday. Before this week, the transportation average's previous high was set July 14.

The index, which consists of airline, trucking, railroad and shipping stocks, has moved higher every day for the past seven trading sessions. For all 19 trading sessions so far in September, transports have had just five days in the red, according to data from FactSet.

According to the widely followed Dow Theory, the transportation average should move in the same direction as the overall Dow in a relatively strong economy. If the transportation average were declining but the Dow had not yet reversed gains, it would suggest shippers in the transportation average have fewer goods to move. That would then mean industrial producers aren't selling as much.

Alongside consumer staples, transports pushed the Dow higher Thursday. The blue-chip index gained 0.21% in early afternoon trading to 22,386.83.

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