Alongside its namesake usage as a yellow school bus, the Transit Coach also served as the basis of motorcoaches and other commercial-use vehicles.

In the 1920s, the company produced the "Gillig top", a lift-off hardtop for open cars that provided retractable side curtains.

[4] Through most of the 1950s, the Transit Coach design had only minor changes, distinguished from later examples by a smaller windshield, lower roofline, different Gillig badging, and dual (instead of quad) headlamps.

[4][5] With the acquisition of the tooling from Kenworth, the roofline of the Transit Coach was introduced with redesigned front and rear roof caps.

[5] As another addition, the Model 534 was a rear-engine bus powered by a Ford Super Duty gasoline V8 (replacing the Hall-Scott and International Harvester engines).

The Model 743DT-16 was introduced, expanding from 13 to 16 rows of seating by extending the body to 41 feet long, requiring tandem rear axles.

[5] In 1974, the interior of the Transit Coach underwent a revision, with a molded-fiberglass dashboard replacing the previous all-metal design.

[5] In April 1977, federal safety standards went into effect in the United States, intended to improve the crashworthiness and structural integrity of school buses.

In compliance, manufacturers had to produce stronger bodies to better survive crashes and rollovers, seats had to adopt compartmentalization as a passive restraint system.

In a major change, the windows were changed from a drop-sash configuration to a larger split-sash design (used on all school buses except the Crown Supercoach), the guard rails on the side of the bus were revised for the first time, as the guard rail below the windows matches the two on the lower body, replacing the previous set of four (used since the 1940s).

At the same time Gillig had facelifted the Transit Coach, two East Coast manufacturers (Superior and Ward) had closed their doors; several others were also struggling financially.

Alongside the recession economy, student population growth had largely plateaued, as the entire Baby Boom generation was past the age of secondary education.

Through the production of the Transit Coach, Gillig used the following numbering system to designate school bus models.