Shadowing Effect

• Shadowing is one of the main problems concerning radar guns in use today. This occurs when an officer's radar gun picks up a large moving object instead of the passing terrain, which then causes it to add the difference in vehicle speeds to the actual speed the target is traveling at. This produces a result that is much higher than the target vehicle's actual speed and may cause an officer to pull you over.
  
  

Weather

• The weather in the environment surrounding the radar gun in question plays a large role in the accuracy and effectiveness of a radar gun. Heavy rain, fog and snow all reduce the effective range of radar guns, and can even cause false readings without the presence of a vehicle.
  
  

Terrain

• The terrain in which the radar gun is being used needs to be considered when dealing with readings from modern radar guns. Because the radar has no sense of direction, radar guns in use on roads and highways that have traffic flowing in multiple directions may be overshooting its intended target and reading the speed of another car. This is a big problem in hilly areas as well where radar guns may be picking up a vehicle that is coming down a distant hill rather than coming up the nearest hill.
  
  

Microwave and Radio Signals

• Objects that produce radio or microwaves also affect the accuracy of a radar gun. Radar from nearby airports, CB or ham radio transmissions, UHF or VHF signals, cellular phones, neon lights, power lines and substations, two-ray radios and even faulty wiring on a car's spark plugs can all cause erroneous readings when using a radar gun.
  
  

Mechanical Interference

• Mechanical interference happens when the radar gun picks up a different moving object than what was originally intended. Roadside signs or billboards that rotate, flash or move are common forms of mechanical interference, but even a moving fan on a vehicle's engine may be mistakenly targeted instead of the intended vehicle.