A Fresnel lens is a thin lens attached to the passenger side window on a heavy vehicle. The driver then gets a wide-angle view as they look through the lens. This assists the driver to see in their blind spot and notice other road users who may otherwise have been hidden.
Transport for NSW has released their Fresnel lens trial research report which shows 15% of the drivers involved stated that the Fresnel lens had helped them to avoid a probable collision or near miss one or more times (during the trial) and 13% that it had helped them avoid a collision one or more times.
Check out the report, here:
https://roadsafety.transport.nsw.gov.au/downloads/fresnel-lens-trial.pdf
Photos: Aide automotive, Truck and Driver, TfNSW.