The MBTA has contracted with Springfield-based CRRC to design and manufacture a fleet replacement encompassing 152 new Orange Line vehicles and 252 new Red Line vehicles. MBTA photo

After two delays in rolling out new Orange Line trains, a top MBTA official said Monday he is “confident” that the first cars are still on track to enter passenger service in mid-summer.

Work continues on testing a signaling system for the new trains, which were initially supposed to begin running in January before complexities prompted delays. MBTA Deputy General Manager Jeff Gonneville said an independent safety assessment key to the project’s completion will likely be done by July, and final approval should follow soon afterward.

“Once that’s completed, we will be able to finish the remaining things we need to be completed,” Gonneville said at a Monday meeting of the T’s board. “We are progressing to the schedule, and we are still on track to have that first six-car set enter revenue service this summer.”

The start date for the new cars, the first of 152 to be delivered, had already been pushed from winter to spring and again from spring to summer as issues arose finalizing the signal system designed by Alstom, a company subcontracted by Chinese manufacturing firm CRRC. MBTA officials said one component of the signals is “vital” and needed updated software to work.

Despite the delay, Gonneville said in March that all 152 vehicles remain on schedule to be built, tested and delivered by December 2021 to replace the entire existing Orange Line fleet.