Whether Highway M is open
Checking whether Highway M is open requires looking at a specific route segment rather than assuming a statewide route number behaves the same along its whole length. A closure notice can come from a crash, flooded road surface, snow, construction, or reduced visibility. If you are planning a trip, confirm the advisory time and affected lanes for the exact county or milepost you will use.
Essential answer
The essential answer is that Highway M may be open for most traffic while one route segment is closed or restricted for maintenance, a collision, or weather-related hazards. Route numbers are corridor-wide identifiers, not guarantees that every mile is passable. A closure notice normally names the section by crossroads, county line, or nearby town, and that geographic scope changes the answer for drivers approaching from different directions.
Motorists should check the advisory time and affected lanes before departing, because a temporary daytime work zone may close one direction while leaving the other open under flagger or signal control. Visibility conditions can also shorten the usable portion without closing the full route. The practical next step is to treat Highway M as open unless an official road advisory describes the specific segment on your intended path.