Measuring the distance a motorist gives a cyclist when overtaking is usually done by "eye" or by estimating distance from video recordings, both of which can suffer from inaccuracies. Now an American company has created a handlebar sonar unit.
The C3FT was designed by Austin-based engineering firm Codaxus for a US police force in a State with a "3 foot passing law". However, the unit could be used by academics, local authorities and police forces worldwide. Video-equipped cyclists now reguarly post footage of close overtakes but the cameras favoured by "helmetcam" cyclists often give distorted wide-angle views.
The unit uses an ultrasonic detector to monitor overtaking distances and transmits this information on a numeric display. Buzzers and LED indicators are set off when a motor vehicle crosses the preset distance threshold. With a Go-Pro on the handlebars, pointed at the display and at the overtaking vehicle it would be possible to record incriminating information. In the US, 26 states have "3 ft" laws, although they have so far been tough to police.
Rule 163 of the UK Highway Code states that motorists should give as much room to cyclists as they would give when overtaking another car. This is illustrated with the motorist taking a position in the opposite carriageway, a manoeuvre demonstrated by a "how to" video produced by the Bicycle Association and British Cycling, and starring Chris Boardman.