Now how did I know that this was a Bones question? I will certainly miss them.
The difficulties in a collision enquiry? Where do I start?
Apart from the location, which isn’t always on the road, or in sight of the road. I have just dealt with 60 plate Range Rover Vogue (£80K), that drove onto the downland at Beachy Head, went some 300 metres until ditching it down the hillside onto the cliff top.
Even on the road, the weather can be a problem – rain masking tyre marks, the cold slowing my working, fog for photography.
Managing to determine whether there were any pre-existing mechanical faults with a vehicle that may have caused or contributed to the collision, is quite often challenging. The crash damage makes working within the vehicle difficult, even trying to check brakes and steering is often a challenge. Furthermore, biohazards, such as blood and body parts/tissue deposits, within a vehicle are also a problem. Then there are the vehicle fluids, brake, hydraulic, power steering, fuel, etc..
A lack of witness testimony may also hinder an investigation, especially with single vehicle crashes.
Trying to determine the causation factor(s) is also a challenge. However, by keeping to scientific protocols and the conventions of maths and physics, the problem solving is the attraction to the job. If it was too easy then it wouldn’t be so rewarding when I finally publish my report and take it to court.