2008-07-14 - Rider Down/Fatality, Grays Inn Road

Bingo, got it !

You need to make the sensor directional.

On a rolling stop the stationary street furniture is moving from the front to the rear of the lorry. A cyclist coming up the side will be moving in the opposite direction, from the rear to the front.

A row of small infared sensors along the cycle side of the lorry would know the direction of the object - that is breaking it's beam - is moving in by sensing the order of the return signal(s). Again cheap stuff, off the shelf components, tiny PSB for the brain, row of sensors - this thing would obviously have to be retro fitted and is so simple that it could literally be stuck (self adhesive) or bonded on to the side of the truck at the specified/recommended height.

So I prayed to my 'higher power' Tynan and he/she/it intuitively told me to go look in the MAPLIN's catalogue under alarms. Maybe someone already makes a suitable proximity sensor or at least one that could be modified as a prototype?