Which of the following is NOT an optional feature for Texas school buses?

The moveable stop arm is considered an optional feature for Texas school buses, as its installation is not mandated by state regulations. This means that while many school districts may choose to equip their buses with a moveable stop arm for enhanced safety, it is not required by law.

In contrast, the other features listed, such as roof top strobe lamps, emergency exit lights, and warning lights, serve critical safety functions and are typically required on school buses to ensure the protection of children while boarding and alighting the bus. These elements contribute to better visibility and alert other drivers and pedestrians to the presence of a stopped school bus. Thus, the distinction lies in the necessity of the features: those that are required are essential for safety compliance, whereas the moveable stop arm is implemented at the discretion of the school district.