The offense of speeding often serves as the basis for a traffic stop that later ripens into an arrest for DWI. In such instances, law enforcement usually employs RADAR technology to justify a stop for speeding, often courtesy of a “radar gun”. RADAR stands for radio detection and ranging; speed is measured by assessing the change in frequency of reflected radio waves.  RADAR makes use of a scientific principle-the “Doppler Effect”-the change in frequency of reflected radio or sound waves as an object moves toward or away from one’s location. The timeworn example of the “Doppler Effect” is the changing pitch of a train whistle as it moves down the track. Utilizing “Doppler", the velocity of an object is then directly proportional to the change in frequency of the reflected wave. Texas courts have long approved of RADAR as a reliable method for measuring the speed of a vehicle.

A second technology-LIDAR, is also commonly employed to justify stops for speeding. LIDAR stands for Light Detection and Ranging. LIDAR utilizes light waves emitted with a laser device to precisely measure distance. The simple calculation of distance traveled (of the light reflected off a traveling object) divided by time of travel equals the object’s speed. Unlike RADAR, Texas courts curiously have not yet endorsed the technology as reliable. According to the Waco Court of Appeals, “there are no Texas authorities confirming the reliability or admissibility of LIDAR technology.” Hall v. State, 264 S.W.3d 346 (Tex. App.-Waco 2008). To fulfill the trial court’s role as “gatekeeper” of the admissibility of evidence, a reliability determination of some sort must first be made before evidence, such as LIDAR, is admissible in a criminal case.  In Texas, Kelly v. State, 824 S.W.2d 568 (Tex. Crim. App. 1992) must be followed.

In Hall v. State, 297 S.W.3d 294 (Tex. Crim. App.-2009) the Court of Criminal Appeals upheld the Waco Court of Appeals determination that the state’s failure to proffer any evidence of the reliability of LIDAR evidence rendered a stop for speeding illegal in a DWI prosecution. The Court left undecided how much evidence of reliability would be required before LIDAR would be admissible in a pretrial setting.

Until such time as Texas courts acknowledge the reliability of LIDAR, a probable cause challenge might prevail if insufficient evidence exists as to reliability of the technology.