Common Radar Errors: Cosine Error

The use of radar guns is common practice on New Jersey roadways to assist police in enforcing maximum speed limit laws, but New Jersey traffic ticket attorneys frequently see them used incorrectly. Traffic radar works on a fairly simple principle: a radio antenna projects a microwave beam at an object and is reflected back to the projection device, the radio is tuned to the required frequency, and a comparison is made from the original frequency sent out by the beam and the reflected frequency. From that comparison, a speed is calculated that is displayed as a digital read-out.

Due both to size constraints (the entire unit must be able to fit on the dashboard of a police cruiser) and financial limitations (law enforcement budgets are tight) the typical traffic radar device has its limitations, as a New Jersey traffic ticket attorney understands.

For example:

1. The radar employs a stationary beam and does not “sweep,” fixing the area that can be under surveillance.

2. The beam can shine in one direction only, either forward or backward, but not in both directions at the same time.

3. It uses a constant beam, not a modulated beam, and therefore cannot distinguish among multiple moving objects within range.

4. As the read-out screen is only digital, the maximum information traffic radar can provide at any one time is one number.

The biggest problem is knowing which vehicle is the source of the reflected signal. For instance, a two lane highway with traffic in both directions may have several cars in range. With only a one number read-out, the operator may not know whether it was the closest vehicle or the largest vehicle that triggered the reading or some other interference or inaccuracy.

One such source of an inaccurate reading may result from what is known as the cosine error. To understand this effect, a New Jersey traffic ticket attorney explains that the speed measured by a traffic radar device is the actual speed of  the vehicle only when that vehicle is traveling directly toward (or away) from the device (in what may be called a “collision course”). Any angle between the vehicle direction and the radar not directly toward or away delivers a relative speed for the vehicle, not an absolute speed.

Further, the cosine effect creates a minimum range. (Vehicles less than the minimum range cannot be measured.) The greater the distance the radar from the roadway lane and the faster the traffic, the greater the minimum range.

These are some of the grounds upon which a New Jersey traffic ticket attorney can challenge your speeding ticket. If you’ve been ticketed for breaking a New Jersey traffic law, do not hesitate to contact experienced New Jersey traffic ticket attorney Dan Matrafajlo at (908) 248-4404 for a free initial consultation.



  • Please fill out the following form and we will contact you as soon as possible.
  • This field is for validation purposes and should be left unchanged.



  • america top 100
  • Cambridge
  • Superlawyers
  • New jercy association for justice
  • AVVO
  • AVVO


Free Case Evaluation

Please fill out the following form and we will contact you as soon as possible.

  • This field is for validation purposes and should be left unchanged.