You bring up a good point. Maybe the best form of protest these days is not to take to the streets but rather take to the highways. Blocking a interstate highway going into/out of a large city might get more attention.
This would be remarkably effective at getting attention, but I'm not sure how beneficial to a cause it would be.
If the purpose is to disrupt travel or commerce, it would most likely achieve it's goal almost immediately. If the purpose is to bring attention to some other issue and the disruption of the highway system is unrelated (or only tangentially related), then the attention would have to be weighed against the negative impression it creates for the many affected.
I don't have the relevant experience in this area to know under what circumstances protests that negatively impact average people succeed in their goals.
This would be a bad idea, tacically and economically. In a protest, at least in the U.S., you can take measures to protect your identity and not carry any documentation, along with the ability to flee on foot in any direction. You also have no tangible assets on you that the government can seize.
In a vehicle protest you forfeit anonymity (lincense plates), ability to split since road-blocks can easily stop you, and most importantly your vehicle might be impounded.
OH it would work. And it's nearly impossible for you to get into trouble. If all the protesters just drove in a circle such as getting on the highway at a specific ramp and getting off at a specific ramp just to get back on. They would create a massive bottle neck not only for those 2 ramps but for the roads that connect to them. There's no law that says you can't joy ride or that you must avoid congested traffic. A group of only 100 people could very easily find a bottle neck on their local highway and exploit it.
In some places, "Disrupting the flow of traffic" is illegal. For example, driving at 55 mph on the highway is legal. However, driving next to someone, both going 55 mpg, would be illegal, as it disrupts the flow of traffic.
Don't take this the wrong way, but I don't care if you're protesting to support feeding starving kids, if you actually block traffic on a highway I will vote against your pet issue 100% of the time.
You point out an additional problem with protests: the methods that don't piss people off are ineffective at getting attention, and the methods that get attention just piss people off.
Hence the protest signage posted in the fences of bridge overpasses of divided carriageways (I don't want to involve myself in an east coast/west coast debate on terms)
