In the United States, federal law mandates that every car must have at least two mirrors. One of these must be an outside mirror on the driver's side, providing a view of the highway to the rear. The second mirror can be either an inside rearview mirror or an outside mirror on the passenger's side. Essentially, the driver must have a view of at least 200 feet to the rear. While many modern cars come with all three mirrors for optimal safety, the legal minimum is two.
This requirement is defined by the Federal Motor Vehicle Safety Standard (FMVSS) 111. The regulation is designed to give drivers a sufficient field of view to compensate for blind spots. The inside rearview mirror is the primary mirror for viewing traffic directly behind you. The driver's-side outside mirror is critical for lane changes and merging. While not federally required, a passenger-side mirror is highly recommended and is standard on virtually all new vehicles sold today.
The effectiveness of these mirrors depends on proper adjustment. You should be able to see the edge of your own vehicle in the side mirrors and have an unobstructed view straight back in the center mirror. Here’s a quick comparison of the mirror types:
| Mirror Type | Legal Requirement? | Primary Function | Key Consideration |
|---|
| Inside Rearview Mirror | Can be one of the two required mirrors. | Viewing traffic directly behind the vehicle. | Must be kept clear of obstructions. |
| Driver's-Side Outside Mirror | Mandatory. Must be one of the two. | Monitoring the left-side blind spot for lane changes. | Often convex for a wider field of view. |
| Passenger-Side Outside Mirror | Not federally required, but standard. | Monitoring the larger right-side blind spot. | Crucial for safe merging and parking. |
If your passenger-side mirror is broken, you are still legal to drive as long as the other two are functional. However, for maximum safety, ensuring all three mirrors are in good working order is the best practice.
