High viz is bullcrap, it's all about contrast. When riding around in bright environments highviz will work against you. When it's dark your lights will do more than the highviz. Only once in my 10 years / 300.000km's did I have a moment where I thought a fellow biker should work on his contrast. Only once, and that's year round riding.
https://www.youtube.com/watch?v=JgLpZ1nbya8and the aftermath:
https://www.youtube.com/watch?v=HfTR90n4Hd8Three bikecops were escorting an ambulance with the van driver (2nd link) who was severely injured.
1: Multiple injuries at a Traffic accident on the A7 (highway)
2: A van drove into a car and came to a stop against a tree (please note highway speeds in NL at the time were 120km/h)
3: The van driver was rushed to the hospital
4: The ambulance was escorted by three police officers.
5: One of the officers conducted traffic to the left lane of the highway (this was at the otherside of the highway where the accident happened, to make sure the ambulance could smoothly enter the highway)
6: And he was hit a car driver that didn't pay attention