Why should a driver avoid passing other vehicles while driving in fog?

Explanation

A driver should avoid passing other vehicles while driving in fog because a safe pass depends on seeing oncoming traffic far enough away and judging enough clear distance to complete the maneuver and return to the lane, and fog's reduced visibility makes both of those judgments unreliable. Fog is not named anywhere in the required knowledge topic for extreme driving conditions, 49 CFR 383.111(a)(12), whose examples are bad weather (snow, ice, sleet, high wind), hot weather, and mountain driving; the closer match is the broader safe-operations umbrella at 49 CFR 383.111(a)(1)(ii), "procedures for safe vehicle operations," which points generally at driving safely rather than naming any specific maneuver, so the specific guidance to avoid passing is standard driver-training practice rather than a codified federal rule. The other options fail for a shared reason: each invents a restriction or consequence, a lane-count-based prohibition, an automatic following-distance change, or a voided insurance policy, that does not exist and does not address the actual visibility problem that makes passing unsafe.

Source: 49 CFR 383.111(a)(1)(ii)