The Orange Line operates during normal MBTA service hours (all times except late nights) with six-car trains.

The stations were richly decorated with tile work, mosaics, and copper; after criticism of the large Tremont Street subway headhouses, most entrances were comparatively modest and set into buildings.

[3] The Boston Elevated had long-term plans to continue this extension further north to Malden, a goal which would only be achieved decades later, under public ownership and not via the Everett route.

[3] In 1938, the remainder of the Atlantic Avenue Elevated was closed, leaving the subway as the only route through downtown – what is now the Orange Line between Haymarket and Chinatown stations.

On December 5, 1960, the MTA began operating "modified express service" on the line during the morning rush hour.

Every other train bypassed Green Street, Egleston (southbound) or Northampton (northbound), Dover, and Thompson Square stations.

After taking over operations in August 1964, the MBTA began rebranding many elements of Boston's public transportation network.

Colors were assigned to the rail lines on August 26, 1965, as part of a wider modernization developed by Cambridge Seven Associates.

[3] The Boston Transportation Planning Review looked at the line in the 1970s, considering extensions to reach the Route 128 beltway, with termini at Reading in the north and Dedham in the south.

The extension was unique among Boston transit lines as it contained a third express track between Wellington and Community College stations.

[12] As a result, instead of an 8-lane Interstate highway with a relocated Orange Line running in its median (in a manner similar to the Chicago Transit Authority's Dan Ryan, Congress, and O'Hare branches), the space would be occupied by the realigned Orange Line, a reconstructed three-track mainline for Amtrak's Northeast Corridor and MBTA Commuter Rail trains, and a linear park.

Between April 30 and May 3, 1987, the Washington Street Elevated south of the Chinatown station was closed to allow the Orange Line to be tied into the new Southwest Corridor.

Instead of rising up to elevated tracks, it now veered west at the Massachusetts Turnpike and followed the Pike and the old Boston and Albany Railroad right-of-way to the existing MBTA Commuter Rail stop at Back Bay.

This MBTA right-of-way is also shared by Amtrak as part of the national Northeast Corridor intercity passenger rail service.

In 2002, Phase 1 of the Silver Line bus rapid transit was added to connect Washington Street to the downtown subways, attempting to address this service need.

[18] In the early 2000s, Somerville began planning an infill station between Sullivan and Wellington to serve the new Assembly Square development.

The aboveground sections of the Orange and Red lines were particularly vulnerable due to their exposed third rail, which iced over during storms.

Starting in 2015, the MBTA began implementing its $83.7 million Winter Resiliency Program, much of which focused on preventing similar issues with the Orange and Red lines.

The Southwest Corridor section of the Orange Line is located in a trench and is protected from the worst weather, but the 1970s-built Haymarket North Extension had older infrastructure and was in worse shape.

That section is receiving new heated third rail, switch heaters, and snow fences to reduce the impacts of inclement weather.

[29][30] During the closure, the MBTA conducted accelerated repairs to track, ties, signals, and concrete walls, as well as replacing two crossovers.

[33] On October 25, the MBTA sent a letter to Senator Ed Markey, who had been investigating the project, detailing work needed during November and December to lift remaining slow zones, ranging from always-planned to unexpectedly necessary tasks.

[51] The Board forwent federal funding to allow the contract to specify the cars be built in Massachusetts, to create a local railcar manufacturing industry.

[52] In conjunction with the new rolling stock, the remainder of the $1.3 billion allocated for the project would pay for testing, signal improvements and expanded maintenance facilities, as well as other related expenses.

Several months earlier, the first two trainsets were taken out of service due to safety issues following the inadvertent opening of a passenger door while the train was in motion.

[60] Cars were also rechecked in early December 2019, after issues with sounds combined with passenger overload necessitated removal from service.

[65] The CRRC cars remained out of service as of July 2021; defective side bearer pads were identified as a contributing factor.

These dampen the movements of the trucks (which include the wheels) with respect to the car bodies, but were found to be wearing in such a way as to produce too much friction.

[70] In December 2022, some new cars were removed from service due to failed power cables causing electric arcing on axles.

Delays began to accumulate in 2019, and then facilities in China and Springfield had to shut down and operate at reduced capacity for parts of 2020 due to the COVID-19 pandemic.