LTi 20-20

Picture of LTi 20-20The LTi 20-20 Speedscope is the most common mobile speed measuring system operated by police forces and, particularly, so-called "safety camera" partnerships.

The system consists of two main components:

  • Laser head with integral display
  • Video recorder


Below you can see what the video replay of the LTi 20-20 system looks like, and the information shown on it.

LTi 20 20 video screen

Click here to view the image full-size

The following information is contained in these fields (this letter from ACPO may help you to understand it better):

Time, Date

The time and date when this frame was recorded.

Frame count

The PAL video records 25 frames per second, each made up of two interleaved scans. The frame count is the number of these interleaved "frames" since the start of the second shown in the time field.

"NR" just stands for "New Record".


A number of error conditions can occur when using the equipment, and these are recorded on the video. Some codes that are relevant to the "target" are:

  • Timeout
    The laser gun takes the speed reading and it appears on the screen then, about four frames later, the word "Timeout" is added to the display (i.e. 4/25 seconds later). This message indicates a time-expired speed-measurement. This is to prevent any possibility of recording the speed of one vehicle, and then just pointing the camera at other vehicles and telling everyone that they were doing 140 mph! So there should be about four frames, before the one that they have sent to you, without the "Timeout". If there aren't then the speed they measured was the speed of someone else's car! This link will take you to an example of this.
  • Error 01
    Target out of range or too close
  • Error 02
    Loss of target due to beam interruption or target going out of range
  • Error 03
    Unstable reading due to poor aim or panning off of target
  • Range
    Range to the target measured by the laser
  • Speed
    Target speed calculated from a succession of range measurements. It appears as a negative number if the vehicle is moving away from the device.
  • Reference number
    The 8 digit number is user-definable. In most forces it carries the officer's number (in this example the last 3 digits) and then a site location reference number (the first 5 or so digits).


LTi 20 20 video screenThe operator can also manually set a speed threshold. When he does this, a "*" marker appears in the frame if a speed reading is obtained that's higher than the preset threshold, as shown in this frame.

Case File example

Below are four stills taken from the video obtained from this Case File, which illustrate a number of these features and ACPO guidelines describe how it should be operated:

Video image 1Timeout

It's been too long since the laser measured the speed for the reading to be considered valid

Video image 2Error 03

Unstable reading due to poor aim or panning off of target

Video image 3*

Not surprisingly, the recorded speed is above the pre-set threshold! The device has also timed out since doing its speed calculation.

You should view the video in real time to decide for yourself how accurate this speed "reading" is!

Video image 4Error 02

Loss of target due to beam interruption or target going out of range

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