Radar Speeding Ticket California
Police radar is the most common speed detection method in California. Knowing how it works, and where it fails, is the basis of a strong defense.
Radar Ticket Quick Facts
How Police Radar Works
Police radar uses the Doppler effect to measure speed. The device emits radio waves that bounce off moving objects. By measuring the frequency shift in the returned signal, it calculates speed.
Types of Police Radar
- Stationary radar: Officer is parked, radar aims at traffic
- Moving radar: Officer measures speed while driving
- Instant-on radar: Activated only when targeting a vehicle
Radar Limitations and Errors
Calibration Issues
Radar devices need regular calibration to stay accurate. Calibration involves:
- Factory calibration (annual or bi-annual)
- Tuning fork tests (before and after each shift)
- Internal calibration checks
If calibration records are missing, outdated, or show issues, the radar evidence may be questionable.
Cosine Effect
Radar is most accurate when aimed directly at an approaching or departing vehicle. When the angle increases, the reading becomes lower than actual speed. This "cosine effect" can create measurement errors.
Interference Sources
- Other vehicles: Radar may lock onto a larger or closer vehicle
- Power lines: Can create false readings
- Radio transmissions: May interfere with signals
- Fan interference: The patrol car's own systems
- Reflective surfaces: Signs, buildings, guardrails
Operator Error
- Targeting wrong vehicle in traffic
- Incorrect device operation
- Failure to verify reading with visual estimate
- Not accounting for environmental conditions
The Speed Survey Defense
Critical: California Vehicle Code 40802 requires a current speed survey for radar enforcement on roads with prima facie speed limits. If the survey is expired, radar evidence may be inadmissible.
What Is a Speed Survey?
A speed survey is an engineering study that determines the appropriate speed limit for a road based on traffic flow, road conditions, and safety factors. Since AB 382 took effect on 1 January 2026 an engineering and traffic survey is valid for 5 years, 7 where the conditions in CVC 40802(c) are met, and up to 14 where a registered engineer finds no significant change in roadway or traffic conditions; the rule does not reach every road, and excluding the measurement is not a dismissal.
When the Defense Applies
- Roads with 25, 35, 45, 55 mph prima facie limits
- NOT freeways (65/70 mph limits are statutory, not prima facie)
- Speed trap exception requires valid survey
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Building Your Radar Defense
Key Questions to Raise
- Was the radar properly calibrated before the shift?
- Is the officer certified to operate radar?
- Is there a valid speed survey for the road?
- Were there other vehicles that could have been targeted?
- What was the angle between the radar and your vehicle?
- Were there any interference sources present?
- Did the officer verify the reading with a visual estimate?
Evidence to Request
- Radar unit calibration records
- Officer's radar certification
- Speed survey for the road (request from local traffic engineering)
- Radar unit maintenance log
Common questions
Frequently asked questions
Can radar guns be wrong?
Yes. While generally accurate, radar can produce incorrect readings due to calibration issues, interference, operator error, or targeting the wrong vehicle. No technology is 100% reliable.
Is radar evidence always admissible?
No. Radar evidence can be excluded if the speed survey is expired, the device wasn't properly calibrated, or the officer wasn't properly certified. These are grounds for dismissal.
What's the difference between radar and LIDAR?
Radar uses radio waves and can track multiple vehicles; LIDAR uses laser light and targets specific vehicles with greater precision. Both have their own vulnerabilities and defense strategies.
Should I mention I have a radar detector?
Radar detectors are legal in California for personal vehicles. Whether you have one is irrelevant to whether you were speeding. Focus your defense on the radar evidence, not your equipment.
Can you fight a radar speeding ticket in California?
Yes. Radar evidence can be challenged on multiple grounds: calibration issues, officer certification, speed survey requirements, interference, and targeting errors. Many radar tickets are dismissed through Trial by Written Declaration.
How accurate are police radar guns?
When properly calibrated and operated, radar is generally accurate within 1-2 mph. However, accuracy depends on proper maintenance, calibration, training, and environmental conditions. These factors create opportunities for defense.
What is the speed survey defense for radar tickets?
Where a posted prima facie limit rests on an engineering and traffic survey, CVC 40802 and 40803 can keep a radar or lidar reading out of evidence if that survey is not current. Since AB 382 took effect on 1 January 2026 a survey is valid for 5 years, 7 years where the conditions in CVC 40802(c) are met, and up to 14 years where a registered engineer evaluates the segment and finds no significant change in roadway or traffic conditions. It does not reach every road: local streets and roads, school, senior and business districts, and limits set by statute are treated differently, so check which category yours falls into. Excluding the measurement is not the same as a dismissal.
Can radar pick up the wrong car?
Yes. Radar measures the strongest signal return, which isn't always the intended target. Large vehicles, multiple vehicles, and reflective surfaces can cause the radar to read a different vehicle's speed.