Using the BBC photo this appears to be the carriageway at the point they were travelling. What may be of relevance is the lay by. The lorry may have been turning into it (classic left hook) or they were already there and the driver couldn't stop/swerve. I do wish the police would routinely publish and publicise the forensics when the coroner has done his work so we, and drivers, may learn from other people's tragic mistakes. More important than punishment.
https://maps.google.co.uk/maps?q=Summercourt,+Cornwall&hl=en&ll=50.364271,-4.980927&spn=0.012086,0.033023&sll=51.48931,-0.08819&sspn=0.755048,2.113495&oq=summercourt,+corn&hnear=Summercourt,+Cornwall,+United+Kingdom&t=h&layer=c&cbll=50.364362,-4.980824&panoid=HT6yt_ARq1M_1I1ngZRg5A&cbp=12,45.26,,0,4.8&z=16
It is certainly a road I would avoid (and appears to be avoidable by a lovely lane just to the north).
https://maps.google.co.uk/maps?q=Summercourt,+Cornwall&hl=en&ll=50.364271,-4.980927&spn=0.012086,0.033023&sll=51.48931,-0.08819&sspn=0.755048,2.113495&oq=summercourt,+corn&hnear=Summercourt,+Cornwall,+United+Kingdom&t=h&layer=c&cbll=50.364362,-4.980824&panoid=HT6yt_ARq1M_1I1ngZRg5A&cbp=12,45.26,,0,4.8&z=16
It is certainly a road I would avoid (and appears to be avoidable by a lovely lane just to the north).