What is one of the effects of marijuana on driving ability?

Marijuana use significantly impairs concentration, which is critical for safe driving. When a driver's ability to focus and pay attention is compromised, it can lead to distraction and reduced awareness of surroundings, making it difficult to respond appropriately to road conditions, traffic signals, and the actions of other drivers. Impaired concentration can slow down a person’s ability to process information and react to situations that require quick thinking, such as stopping for pedestrians or reacting to sudden obstacles.

While increased reaction time might also be an effect of marijuana, it is the impairment of concentration that directly impacts a driver's ability to navigate safely through various driving scenarios, contributing more broadly to the risk of accidents. Similarly, the notions of improved coordination or enhanced decision-making do not align with the effects of marijuana, as the substance generally leads to adverse outcomes in those areas as well.