The basic speed law, Vehicle Code 22350, makes it illegal to drive faster than is safe for conditions, even when you are under the posted limit. It is a common reason officers give for a traffic stop, including stops that turn into DUI investigations. I am Joel Brand, and here is what the statute requires and how it factors into a DUI case.
The text of the law
Vehicle Code 22350. No person shall drive a vehicle upon a highway at a speed greater than is reasonable or prudent having due regard for weather, visibility, the traffic on, and the surface and width of, the highway, and in no event at a speed which endangers the safety of persons or property.
What the statute requires
Section 22350 does not set a number. It is a conditions-based rule: you may not drive faster than is "reasonable or prudent" given the weather, visibility, traffic, and the surface and width of the road. That means you can violate the basic speed law while driving below the posted limit, for example doing 50 in a 65 zone during heavy fog or rain, and you can sometimes comply with it slightly above an outdated posted limit on a clear, empty road, though that is far harder to argue. A violation is an infraction that adds one point to your record under the DMV point system.
How it differs from the maximum speed law
It helps to keep the two speed statutes straight. The maximum speed law (VC 22349) is a flat numerical ceiling, broken simply by exceeding the absolute limit. The basic speed law (22350) is about going too fast for conditions, even under the posted limit. The full comparison is in the difference between VC 22349 and VC 22350. The distinction matters because the basic speed law is far more subjective, which cuts both ways.
"Reasonable or prudent" is a judgment call
The defining feature of the basic speed law is that it rests entirely on an opinion about what was safe. There is no fixed line; whether a given speed was "reasonable or prudent" for the conditions is a judgment the officer made in the moment and that we can later contest. Two reasonable people can disagree about whether 40 miles per hour was too fast for a particular wet curve. That built-in subjectivity is what makes the charge contestable, but it also means an officer can attach it to almost any stop, so it deserves close scrutiny.
Why it matters in a DUI
In a DUI, the basic speed law usually serves as the officer's stated justification for the stop, or as supposed evidence that the driving itself was impaired. But driving a bit fast for conditions is something sober drivers do all the time, and it is not proof of impairment. The two questions, whether you drove unsafely for the conditions and whether you were impaired by alcohol or drugs, are separate, and each requires its own proof.
Challenging the stop
When the basic speed law is the basis for the stop, I examine whether the officer's conclusion that your speed was unreasonable actually holds up against the real conditions, and whether any speed measurement is reliable. If the stop does not survive scrutiny, a motion to suppress under Penal Code 1538.5 can follow, and suppressing the stop can unravel the DUI, because everything the state has flows from that initial contact.
The speed measurement still has to be reliable
Even though 22350 is about conditions rather than an absolute number, the prosecution still usually relies on a measured speed to argue you were going too fast. That measurement is not infallible. Radar and lidar require proper calibration and a trained operator; pacing depends on the officer's own speedometer and a steady following distance. And where a posted limit is enforced by radar, the speed-trap rules require a current engineering and traffic survey, without which the radar evidence can be inadmissible. I request the calibration logs, the operator's training, and any required survey as a matter of course.
Conditions cut both ways
Because the statute turns on weather, visibility, traffic, and the road, those same conditions are the heart of the defense. If the road was clear, dry, well-lit, and empty, then a moderate speed was reasonable and prudent almost by definition, which undermines the charge. Conversely, if the officer ignored the actual conditions and simply assumed any speed was unsafe, that assumption is contestable. I gather the weather records, the lighting, the traffic level, and the road's design for the time and place in question, because the prosecution has to prove the speed was unreasonable for those specific conditions, not just that you were moving.
Points, fines, and the record
As a standalone infraction, a basic speed law violation carries a fine plus assessments and one point. On its own that is minor, but combined with a DUI it adds to your record and can be addressed as part of the overall resolution. Keeping the point off matters for insurance and for the DMV's negligent-operator thresholds, where accumulating too many points in a set window can trigger a separate license suspension.
A speed is not impairment
Prosecutors sometimes lean on a speed to argue the driver was impaired. That inference is weak. Plenty of sober drivers go faster than conditions strictly allow, and a clean driving pattern apart from the speed, no weaving, no near-misses, a normal response to the lights, actually cuts against the impairment theory. I make sure the speed is treated as a traffic question rather than allowed to stand in for the proof of impairment the prosecution must establish through the chemistry and the field evidence.
How it fits the larger defense
The basic speed law issue is one piece of attacking the lawfulness of the stop, the most powerful category of DUI defense. It works alongside challenges to the field sobriety testing and the chemical evidence. See my top DUI defenses, the defenses guide, and the related maximum speed law.
Stopped for speeding and arrested for DUI? Let's talk.
Whether that stop was justified may decide your case, and it is exactly what I review against the conditions and the measurement. Use the free case analysis on this page, or call me directly at (888) 271-6644. I answer my own phone, 24/7.