Id suggest a 30 mile tailback would definitely cause more emissions, the majority of those vehicles are going to be sat with their engines idling, so aircon etc can be used, plus extending the journey times of all those involved will also increase the emissions.
Ill bow to your second point, I really dont know enough about it to argue with you.
For the third, direct protest where the power brokers are, constant and repeated protest. Johnsons schedule is fairly public. Mass protests at every function he attends, every PR/Photo Op, same for other members of the cabinet, same for CEOs of the most polluting companies, inconvenience and disrupt those with the power to generate change.