On the blinding effect of the sun I can state a case in the NE where I have been unable to see clearly enough to be comfortable driving: approaching the brow of the hill on the 3 lane section of the southbound A1 up the Bowes incline. There, cars travel at speeds way above 70mph in the fast lane to beat slower traffic, meanwhile cars and lorries swap lanes on the inner and middles lanes as lorries struggle with the gradient. So, 3 lanes of traffic at varying speeds, pulling out on one another. Picture the rush-hour when at any time the 3 lanes can come to a sudden stop for no apparent reason.
It's the middle of winter, the road is wet and still slippery from the night's frost, it's between 8.30 and 9.30am travelling SE up the hill... it's a unique set of conditions with bright sun shining just above, and parallel to, the road surface with the sun reflecting equally off the road surface.. you can't see outlines or the shadows of the vehicles in front due to the glare.
The sun has just risen above the horizon causing temporary blindness regardless of where you put your visor, even wearing sunglasses the glare is awful. Made worse by those idiot drivers, who have set out without windscreen wash, whose salted windscreens flare even more in the glare- but they carry on expecting the traffic to keep flowing. You can't be sure the cars ahead are still moving so you slow down to a snail's pace to be able to stop in the short distance you can still see, but you are scared [really scared] of being shunted by faster, more ignorant drivers behind you... what do you do?
I avoid the A1 at this time of day in late November/early March in strong morning sun after rain as it is impossible.
If that flyover is in a similar position to the sun in relation to the gradient on a specific day in similar conditions I can easily believe people genuinely cannot see clearly.
Doesn't excuse the accident though.