Which traffic control devices must be certified according to NCHRP 350?

The correct answer highlights that all traffic control devices must be certified according to NCHRP 350 standards. NCHRP 350 is a set of guidelines developed for the evaluation of roadside safety features, ensuring they perform effectively and safely during crashes. This certification process is critical because it ensures that devices used in work zones, such as barriers, signs, cones, drums, and signals, meet specific criteria for safety and effectiveness. Each type of device must be tested and evaluated for various impacts and scenarios to mitigate risks to both drivers and workers.

While some devices may seem less critical in high-speed scenarios, all traffic control devices play a significant role in guiding, warning, or regulating traffic, making their safety and reliability essential. This comprehensive approach to certification helps maintain a uniform standard across all types of devices, promoting roadside safety in a holistic manner.