In the planning stages, the G Line was known as the San Fernando Valley East-West Transitway and later the Metro Rapidway.

However, political developments stymied these plans: community objections to surface transit along the route resulted in a 1991 law mandating that any line along the route be built as a deep-bore tunnel,[13][14] but a 1998 ballot measure driven by perceptions of mismanagement banned the use of county sales tax to fund subway tunneling.

[19] Then-County Supervisor Zev Yaroslavsky said they initially mirrored the busway concept based on a similar transit system he, then-Mayor Richard Riordan, and other elected officials toured in Curitiba, Brazil.

[20] On June 23, 2009 construction began on a four-mile (6.4 km) extension from Canoga northward along the Southern Pacific trackbed[21] to the Metrolink station in Chatsworth.

In 2018, this branch was eliminated and replaced with a frequent service local shuttle, leaving the entirety of the Orange Line on the dedicated right-of-way.

[25] In the first year that the busway was open, there were ten injury collisions between vehicles and buses, which were heavily covered in the media.

These include quad-crossing gates at 37 intersections and constructing a mile-long elevated section between Sepulveda and Van Nuys Boulevard.

And while the proposed change in the previous project from priority to preemption at signalized intersections will decrease delays to G Line buses, it will come at the cost of increasing cross-street travel times and reducing their capacity since priority balances the timing needs of busway traffic with cross-traffic versus the more disruptive railroad-style preemption.

)[36] In April 2015, a report prepared for Metro estimated that conversion of the G Line to light rail would take two to three years and cost between US$1.2 and 1.7 billion.

On October 27, 2005, two days before the line's official opening, a motorist driving with a suspended license ran a red light and collided with an eastbound bus at Vesper Avenue.

The G Line fleet is stored and maintained at Metro's Division 8 depot in Chatsworth, which has direct access to the busway.

Prior to 2021, the former G Line fleet used NABI 60-BRT buses which ran on compressed natural gas (CNG).

The on-route chargers, which are manufactured by Siemens to the SAE J3105-1 standard, add about 40 miles (64 km) of range from a seven to ten-minute charge.

[43] As of the end of June 2024, due to heat stress and reliability issues with on route charging equipment, Metro has begun intermittently using 40-foot (12 m) CNG powered buses to supplement the dedicated battery-electric fleet.

[46] This goes back against the G Line's electrification achievement, a long-standing Metro-touted victory[47] in its troubled history of attempting to electrify its bus fleet.