The busway opened in January 1973 to buses only, three-person carpools were allowed to enter in 1976, and the facility was converted to HOT lanes as part of the Metro ExpressLanes project on February 22, 2013.

The busway now carries 16,000 bus passengers per day with 49 buses using the system each hour at peak times[1] and was described by the United States Department of Transportation as one of the most successful HOV facilities in the country in 2002.

[4] The 53 million dollar project was paid with federal, state and SCRTD funding and was also intended to be an experiment testing the feasibility of joint highway-bus operations and to increase the overall people-carrying capacity of freeway corridors.

[3] The eastern section is located in the median of Interstate 10, with only paint lines separating traffic on the busway from the general-purpose lanes.

[9] The El Monte was extended to its present length of 12 miles in 1989 with the opening of a one-mile extension from Mission Road to Alameda Street adjacent to Los Angeles Union Station.

[2] The busway was opened to vehicles with three or more occupants during the 1974 Southern California Rapid Transit District strike, which lasted 68 days between August and October.

[10] Opening the busway to HOVs had only minimal impact on bus running time and transit ridership remained stable.

[15]: 3  In 1998, Metro studied the extension but found it expensive and technically challenging, and to date, there have been no further efforts to connect the busways directly.

Ultimately, the Metro Board of Directors decided to continue running bus routes on both the El Monte Busway and Harbor Freeway as they had before.

The new higher frequency service would be funded by converting both corridors into high occupancy toll (HOT) lanes, to be branded as the Metro ExpressLanes.

The Silver Line began operations on December 13, 2009, with Metro planning to refurbish the aging stations along both corridors over the coming years.

[25] Transit Access Pass (TAP) card ticket vending machines were added to most stations in early 2017 to support all-door boarding on the Silver Line.

[27] On November 1, 2020, a new transitway was opened on the south side of Patsaouras Transit Plaza to serve Union Station, funded in part by Metro ExpressLanes toll revenue.

[31][32] A mix of Los Angeles County Metropolitan Transportation Authority and Foothill Transit bus services utilize the El Monte Busway to operate between Downtown Los Angeles and various points in the San Gabriel Valley and Pomona Valley, as well as the San Bernardino County city of Montclair.

Metro and Foothill Transit offer a reciprocal fare program where pass holders may ride either J Line or Silver Streak buses between Downtown Los Angeles and the El Monte Station.

Metro Express 487 operates all-day, seven days a week; the rest only run during weekday peak periods.