There are two types of speed-related signs on our highways, and they sometimes cause confusion: the advisory speed sign and the regulatory speed limit sign. Understanding the difference between them is helpful for your DMV test and lawful driving.
The Recommended Maximum Speed
An advisory speed sign provides a recommended maximum speed for specific conditions on a road segment, typically around curves, exit ramps, or other areas where potential hazards make driving unsafe at the general posted speed limit. These signs are yellow and black, and you will often see them below a warning sign, such as a curve or slippery road sign.
The key thing to remember is that advisory speed signs are not enforceable by law in the same way as regulatory speed limit signs. They are guidelines based on engineering assessments about road curvature, visibility, and typical vehicle handling factors.
What Is a Regulatory Speed Limit Sign?
In contrast, a regulatory speed limit sign displays the maximum legal speed allowed on a stretch of road under ideal conditions. These signs are white with black lettering and are legally enforceable. Exceeding the speed shown on a regulatory sign can result in a speeding citation, regardless of whether the road conditions seem safe.
State or local transportation authorities set regulatory speed limits based on studies that evaluate traffic flow, road design, and accident history.
Key Differences Between the Two Speed Signs
| Feature | Advisory Speed Sign | Regulatory Speed Limit Sign |
|---|---|---|
| Color | Yellow and black | White and black |
| Enforceable by law? | No | Yes |
| Purpose | Suggests safe speed under specific conditions | States the legal speed limit |
| Typical placement | Curves, exit/entrance ramps, hazard zones | General roadways, highways |
| Based on | Engineering judgment for safe navigation | Traffic studies and legal standards |
The Role of the Basic Speed Law
Should you always follow advisory speed limits?
Even though advisory speed signs are not legally enforceable in the same way as regulatory speed limit signs, drivers are still legally obligated to drive at a safe speed under the Basic Speed Law, which is in effect in all 50 states.
The Basic Speed Law generally states that:
“No person shall drive a vehicle at a speed greater than is reasonable or prudent under the conditions and having regard to the actual and potential hazards then existing.”
Regardless of the posted regulatory speed limit, police can cite a driver for driving too fast for conditions, even if the driver is technically below the legal speed limit.
How the Basic Speed Law Applies to Advisory Speed Signs
Advisory speed signs indicate areas where road conditions, such as sharp curves, steep grades, or exit ramps, require reduced speeds for safe navigation. If a driver ignores the advisory speed and causes an accident, law enforcement can argue that the driver was violating the Basic Speed Law.
For example, a driver takes a curve at the posted speed limit (e.g., 55 mph) instead of the advisory 35 mph, leading to a rollover or skid. Even if the speed limit is not exceeded, the driver could still be ticketed for driving at an unsafe speed under the circumstances.
Legal and Safety Implications
- Legal: Courts often consider advisory speeds as evidence of what a “reasonable and prudent” speed would be. Ignoring them can strengthen a negligence claim in the event of a crash.
- Safety: Vehicles—especially larger ones like trucks and SUVs—may be more susceptible to rollovers or loss of control at speeds above the advisory level.
- Insurance: Being cited for a Basic Speed Law violation or being found at fault in an accident caused by unsafe speed can increase insurance premiums.
