It's actually a lot safer in places that are more congested and have a lot of stop-start traffic. For example, here in the UK, if you sit at the back of a queue

It's actually a lot safer in places that are more congested and have a lot of stop-start traffic. For example, here in the UK, if you sit at the back of a queue of traffic on a motorcycle a truck might not see you and rear-end you. Getting rear-ended by a truck isn't great on a car, but on a bike? Not good. Instead if you filter and split lanes and get to the front of the queue of traffic you're not only safer but also out of the way of that wave of traffic, since you're on two wheels and can accelerate away much faster than the rest of the traffic. This then allows you to have a buffer behind you.