A and C train riders face uneven service, as well as jam-packed trains in downtown Brooklyn, an analysis of the two lines by the MTA found on Friday.

The A is often hit by delays from boat traffic and the opening of the South Channel Bridge in Queens, which is only halted during some parts of the morning and afternoon rush, the analysis found.

The two lines also have some of the oldest subway cars in the system — the C line’s cars were built in 1964, and the A train’s cars in 1976. Some cars lack more modern subway car features, like electronic signs and automatic announcements.

About 800,000 passengers rely on the A and C lines each weekday. The A is the longest line in the city, making it difficult for the MTA to provide steady service. It stretches more than 32 miles, beginning in upper Manhattan and ending at three different place in southeast Queens.

At some point on its route, it connects to every subway line except the No. 6 train.

"The A, C corridor is unique in that the A splits three ways at its eastern end in Queens,” said MTA chairman Thomas Prendergast in a statement.

“It is also exceptionally long and merges several times with other lines. The combination of these traits along with increasing ridership has affected reliability."

To boost A and C service, the MTA said it would revise their schedules, particularly during the morning rush-hour, and focus on getting even spacing on the A train. It will add more crews on the A line to improve train turnaround at terminals, and work on getting longer stretches of time from the Coast Guard where the A line won’t be interrupted by boat traffic.

The MTA will also add platform conductors at the Hoyt-Schermerhorn stop to get trains in and out faster, similar to busy stations like Grand Central Terminal.

The study is the fourth review the MTA has done of a subway line. Similar analyses of the F, L, and G led to better service.

Riders’ advocates who had called for the A and C analysis were frustrated by the analysis.

“Today’s A/C full line review promises a few improvement for riders, like station improvements, adjusting service timing during peak hours, and service increases on Sunday,” said Rebecca Bailin, a campaign manager for the Riders Alliance.

"But we're disappointed that the MTA has decided not to increase service on the A & C during rush hours or take serious measures to decrease crowding across the entire line. Riders are tired of dealing with crowded platforms and trains, and this full line review only partially solves their complaints."