Either they're the utilities are exposed https://www.businessinsider.com.au/ships-anchor-cuts-interne... or the overreaction is very expensive https://www.theguardian.com/world/2014/apr/17/portland-flush...
the CFAA and foreign states not wanting to start a war is seemingly the only thing stopping massive grid failure.
Two people can rent a couple of UHaul trucks and block almost any highway. It will take hours to get the trucks away.
I also remember an estimate that ~10000 trained saboteurs can bring the whole country to a grind. It's quite cheap and fast to blow stuff up, and much more expensive and slow to restore it.
I see this as a complete win. It would quickly result in cops aggressively enforcing the existing traffic laws that already make this kind of behavior ticket-able.
It will be a glorious day when driving like a slug carries more risk of being stopped and ticketed than speeding, rolling an empty 4-way stop or otherwise driving like a normal person.
You can screw over an entire city for a week+ by renting a car, parking it in a particularly busy street, and then leaving it there. If you + a few of your friends do this, then you can gridlock the entire traffic flow of a city, as tow trucks cannot get into the area.
The police were able to pull them over and sort them out. I forget what 'public nuisance' law they used, but the police have a wonderful set of things they can arrest people for. Breach of the peace, public order or a good one is conspiracy. Conspiracy can be proved in court but the act at the heart of the conspiracy does not have to be illegal. You could prosecute people for conspiring to share a chocolate bar in theory.
One law the police can truly hang/draw/quarter people for is arson. An 'accidental fire' need cost no more than a box of matches and can definitely sabotage a city. Hence the vast prison sentencing options. I lived somewhere where there was someone setting light to cars at night on our street, they got away with it six or more times and it was crazy how cars would explode the fuel tanks of neighbouring parked cars and melt the windows and guttering of the houses. We had pitchforks at the ready for kids from a neighbouring estate but it didn't turn out to be them. It just took one mentally ill person to put us all on this 'war' footing, suspicious of our neighbours and paranoid.
During the fun years of 'The War Against Terror' the government had to make the threat real with lots of terror drills and implausible scenarios. At one stage there were 'ricin' terror plots where some innocuous plant in someone's front garden was going to kill us all, there was another funny plot where the alleged terror operatives had bought several trillion smoke detectors to get the radioactive gubbins out of them and make a 'dirty bomb'. Obviously this would have killed us all but luckily the 'intelligence' services were onto the bad guys and 'saved the world'.
There was no foreign nation state doing this, the UK government managed to do it all by themselves. They even shut down London's Heathrow in one of these colour coded terror events, inconveniencing many but making the threat seem plausible if nonsensical.
Oddly the terrorists never had a plan that would actually work. There was always a flaw to the story, for instance the likelihood of being able to buy an absurd amount of smoke detectors or the realities of the ricin yield from the castor beans.
It was a bit like video games and movies where the bad guys are predictable and stupid.
Industrial action has been an area of subtle sabotage. In the UK this was a common thing in the 1970's. Cars would make it to the end of the production line with rattles and other defects that just made mass production a farce.
I think the CIA have a manual on how to do this, so a resistance movement in an occupied country can make things grind to a halt, just by being useless at their jobs, never doing anything that could be seen as 'terrorist'.
It seems like it should be fairly good bang for buck, in this sense, to just hire people to drive around kind of slowly and badly. Nothing overtly aggressive, but a few dozen people driving slowly around a few select traffic circles around rush hour should really gum things up.
Even better if you can cajole some people into, say, pulling emergency stops on subways. Note I don't think that's what's happening in NYC, but this case does seem to show that a few people could cause outsized disturbances just by being assholes.