It's frightening how easy it is for an foreign actor to knock out a country's railway system
The attack on SNCF was not "easy". This was a methodical, large scale, coordinated attack. They knew what to take down. How to take it down with least collateral damage. And when each should be taken down. (Order likely counts here. You're trying to plug up tracks.) Point being, these attacks are not "easy". In a place with as much unrest and discontent as France has bubbling beneath the surface, the trains would go down twice weekly, every week, if it was "easy" to do so.
A similar methodical, large scale, coordinated attack on our bridges would shut the system down as well. I won't even mention some other infrastructural assets that, if targeted, easily will shut us down for months because I think they are just that soft as targets. I honestly believe it would be irresponsible to even put the idea out into the ether.
The takeaway here is that if you're dealing with large organizations, with even a modest amount of resources, and a grievance, you're likely dealing with orgs that have a lot of young people they can send to successfully carry out such attacks. Thankfully, these attacks still require a level of technical knowledge that seems to elude such groups. So it's just matter of keeping that information as secure as possible on the one hand. While working towards security and resilience of those assets on the other.
It looks more like an elaborately prepared barbecue party: careful planning, getting all the details figured out ahead of time, coordination and, well, relatively calm execution.
Maybe foreign agents could do it with 50? If they were supported by satellites and other tools to which these attackers likely did not have access. But foreign agents are operating in relatively large teams even for simple missions. I don't think with this level of coordination, and this number of targets, spread over this large a geographic area, any intelligence agency is going to send one guy/gal per target. It only works like that in Bourne and 007 movies.
The only novel thing here is coordination, but it doesn't seem like a huge stretch of the imagination to target the 4th most frequent high speed rail crossroads, which is exactly what they did.
Um, sabotaging any city's water tunnels would make the city uninhabitable for years.
Most frightening experience I ever had as engineer in my life:
I was intern. At a place in a midwestern city where a city's water infrastructure can be monitored. Long story short, I heard "PING". Then three more "PING"s. Then another "PING". Then 2 more. Even as an idiot intern, I knew what the implications were with respect to tensioned concrete. I was thinking in my head, "8 feet diameter. 96 inches." But I couldn't remember the PSI because I probably had already soiled myself. Thankfully there was a grey beard there who coolly looked over at me and said, "Probably want to start shutting that down son."
2 things I learned. Calm is contagious. And our infrastructure is way more frail than should be the case.
Can totally picture
How are you counting this? If you mean Hudson River crossings between NJ and Manhattan, there are five: two road tunnel groups (Holland and Lincoln) and three rail grops (Upper/Lower Hudson and North River). When Gateway is complete (2030s), there will be four rail groups.
But if you mean the entire NYC metro area, there are significantly more: Manhattan <-> Brooklyn alone has the Hugh L. Carey for road traffic, and then six active subway tunnel groups. Manhattan <-> Queens has a similar number.
Real world has lot to learn from IT infrastructure management. :-)
Extra points for putting the large bus or truck on it's side, requiring a crane or much more work to get it on its wheels.
And you don't have to walk off, you can unload your electric scooter and zip away to start your new life as a fugitive.