All organisers are required to complete a risk assessment for each event they run, including reruns of events from previous years.
In reality, very few organisers put any effort at all into their risk assessment. Naming no names, I know of one organiser who had to cancel an event due to ice, on the morning of the event. The next year, there was no note on the risk assessment. Another event sent riders down a road waist deep in water. The following year, no note in the RA.
But risk assessment is not just health and safety. It's an opportunity to put down in writing the things that may go wrong on your event, and to think about how you might (if possible) mitigate those risks. As well as busy junctions, you should also consider risks like getting only a handful of entries, or a crucial control cancelling your booking. What would you do if your only volunteer called in sick, or if you got inured and couldn't test ride your routes. These are all things that happen regularly, yet hardly anyone puts them in their risk assessment.