The Trinity Railway Express (or TRE) is a commuter rail line in the Dallas–Fort Worth metroplex. It was established by an interlocal agreement between Dallas Area Rapid Transit (DART) and the Fort Worth Transportation Authority (The T). Each transit authority owns a 50% stake in the joint rail project and contractor Herzog Transit Services operates the line. The TRE began operating in December 1996.
As of the fourth quarter of 2014, the TRE has an average weekday ridership of 8,200 passengers per day and is the fifteenth most-ridden commuter rail system in the United States. In 2014, the TRE carried 2,293,500 passengers.
Before 2006, the TRE was typically shown as a green line on DART maps and therefore was sometimes referred to as the “Green Line,” but this was not an official designation. In 2006, DART chose green as the color for its new light rail route, the Green Line. Since 2006, the TRE has been shown as a dark blue line on DART maps.

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