To consider a few things. If the car was stopped, then it would have made no difference to the outcome, the poor lad crashed into it.
I believe British Cycling have been working for years on getting marshals allowed to stop traffic, and have seen a "lollipop" sign that says something like "Cycle Event - STOP" just like a crossing patrol sign, in use last season. That secured the junctions. Whatever any petition says, there will be plenty of resistance to anyone but police being allowed to officially stop traffic while they are on the move, and NEG have no more legal powers than anyone else n the road. Legislation takes years - much as we may want something, it simply won't happen.
All that said, it's an awful thing for a young rider to pay with his life for what may have been a simple error, probably we shall never know.
One other point, can anyone recall the last fatal incident in a UK road race? It is, thankfully, a very rare thing, so rare that it made the national papers.