Concrete barricades such as 'k' rails provide the greatest level of safety.

Concrete barricades, such as 'K' rails, are specifically designed to provide a high level of safety in work zones by effectively controlling traffic and protecting road workers. These barriers are robust and can absorb the impact from vehicles, minimizing the risk of serious injuries or fatalities. The solid structure of K rails prevents vehicles from crossing into work zones, creating a physical separation between moving traffic and workers.

Their height and weight contribute to their stability, making them less likely to be displaced by errant vehicles compared to lighter barriers. Using such barricades is essential in high-speed or high-traffic areas where the risk of accidents is significant. Thus, when considering overall safety measures, K rails indeed represent one of the most effective solutions for protecting both workers and drivers in construction and maintenance zones, making the statement true.