It's hard to get information about private rail travel in the US. People in my train communities are very squirrelish about information. They have a 'if you aren't in the know, we wont tell you' attitude. The websites of some of the train car rental companies don't even have pictures of the trains for rent! In some of the websites with pictures, the pictures are tiny, strange and unhelpful. But, spending lots of time in trains communities I do have a bit on knowledge and wanted to share it here.
My knowledge of historical rail travel is more comprehensive. I have a post here that talks luxury, erosion of class boundaries, crime, etc. I wrote the post as a resource for writers, and also take questions on the topic there.
This is a tricky topic to write about because there are so many types of private / privatized train service in the US. The really juicy high end rail travel is a very insular world. I am going to ignore heritage train service, oddballs like The Grand Canyon Railway, and pretty much focus on three categories:
1) Attached to Amtrak - People who own or rent train cars and pay to have them hauled along behind The Empire Builder or some other route.
2) Chartered Service - This is a broad category. There are a number of passenger train services running under their own power on US rail lines that aren't Amtrak. This category includes a lot of museums and tours.
3) Privileged Access - Very little is known about this tier other than it does exist. In the US, cargo has priority over Amtrak for use of the rails on the vast majority of the system. Amtrak owns a small amount of rail itself, mostly in the Northeast Corridor. But if you make a deal with a rail company like BNSF or are BNSF you can do what you want.
There is a lot of overlap between these categories. It appears that some charter services deal with Amtrak, and some make deals with the large rail companies to get the access and reliability usually afforded only to potatoes, oil and other cargo.
Also, as a side note, Alaska has it's own state-run railroad for passengers, cargo and also charter travel. As far as I know, most of the private travel there is chartered by large tour companies or cruise ship companies. There is no connecting line between the Alaskan Rail Road and the main cargo lines of US and Canada, so most private rail cars can't get up there.
I am going to start out talking about the Attached to Amtrak level of service. These privately owned cars are something like vacation homes. Some people have fancy ones only for themselves and guests, other rent them out when not in use to defray costs. People who do this level of service span both the millionaire and billionaire class.
This level of travel can be very luxe, here is the private train of the owner of Patron Tequila:



Images from this article.
If you want to rent a train car and travel on the back of an Amtrak train, I'd recommend budgeting at least $15k/day. Some of the travel websites out there claim it can starts as low as $12k/day, or even $9k. I think those are lowball numbers that don't include many of the taxes and fees. The cost to supply power to a car attached to an Amtrak train is per day is $2,868.00. That's what it costs just to turn the lights on. In addition to set daily costs, there are also per-mile costs to pull the car.
Technically, the federal government stopped allowing this level of service in 2018, citing things such as 'not meeting revenue goals' and other, well, other BS. Private cars are a money maker for Amtrak, but the company is a very strange political football. It's public transit so Republican lawmakers at the national level want to kill it's revenue streams with fire. City and state Republican lawmakers, governors, etc see it as crucial to their economies. Both very rich and poor Republicans tend to be very attached to Amtrak and see it as important to their lives... and there is a whole political thesis paper that could be written about this. All of my train communities got flooded with disinfo for a solid year leading up to the 2020 election claiming that Biden would end Amtrak... which is insane if you know anything about train funding fights or that Biden has had the nickname of 'Amtrak Joe' for at least a decade and a half.
This political tangent is building to something besides me needing to vent about political disinfo about trains I swear.
The end date for private train cars came and went... with no change in how many were spotted by trains enthusiasts. It's like the large corporations and rich people who like their mobile vacation houses and venues to wine and dine clients basically said 'lol no' and kept on booking per usual. Here is a video from 2019 that clearly shows private cars attached to an Amtrak engine. It's strange that the cars are at the front, rather than the back. This older video shows the more typical configuration. While that is one example, I watched as the groups I am in realized that the ban only existed in theory. Articles came out claiming a 'softened' version of the ban was in effect, but, nope, even those restrictions where clearly not being followed at all.
In short, a bunch of rich people ignored GOP attempts to mess with Amtrak because they found it inconvenient. Rules? Rules are for people with less money.
Obvious disclaimer - People across the entire political spectrum love trains. But there is a lot going on with how the super rich use our rail systems and the GOP's complicated relationship with Amtrak.
Since January 2021, Amtrak now openly allows private cars again and has posted information and prices.
The company that makes the most use of Amtrak for pulling private cars is called Charter Steel. They own five restored vintage cars. I spotted one of their cars while on an Amtrak train, which is what lead me to start looking into private rail travel:

This is the picture in question. It's a hard topic to research, and the company having a name like 'Charter' doesn't help. So many google results about chartered train service instead... Also, it's hard to try to find images on Instagram or search subreddits.
I can find lots and lots of pictures of the outside of the car, but sadlyFoamers Rail Fans may be obsessive trainspotters and have databases that track not only cars and engines, but individual parts. I could find out when and were each wheel was made, and if it's a salvage part from another Pullman, but seeing the inside is another story.
This image has been posted several times with the claim that this is the Charter Steel's Club Car:

I don't know if it is. Even if this is a picture, it's a very old one. It's possible, likely even, that the interior has been redone done the snap. I've done several deep dives trying to get more info and to this day, that is all I have to show for it. If it's possible to take a picture through the window that clearly shows the inside, well, my camera can't do it at least. And yes, I have tried!
Chartered Service - I'll go over this briefly due to overlaps with Privileged Access.
There are companies you can hire to do custom rail travel and there is regular service on non-Amtrak passenger rail in the US. One benefit to both Chartered Service and Privileged Access is that there's more places you can go.
Amtrak routes:

Cargo rail in both US and Canada:

The vast majority of Amtrak delays are due to other trains getting priority over them on the US rail system. It's not Amtrak's fault, it's just that our rail system puts potatoes over passengers. Amtrak only owns a tiny bit of actual rail, almost all of it is owned by private companies in the US. With some chartered services can get people the higher level of access usually reserved for cargo.
There are people whose hobby is riding Amtrak's The Southwest Chief over and over again hoping for just the right serious delay so they can take pictures of red rock formation in the American Southwest that are incredibly hard to impossible to legally access. Since the start of the Covid-19 pandemic, there has been rising interest in higher end chartered service in the US providing these views in day light. The Rocky Mountaineer is one such service.
Here is a picture of one of their railcars:

For this and most higher end luxury and heritage rail travel, it is so focused on couples that there isn't even an option to book solo.So if any fellow train lovers are interested in fake-dating...
Privileged Access -
Did you know that railroads are allowed to have their own police forces? With interstate law enforcement authority? Amtrak falls under Federal jurisdiction, but private companies like BNSF get to operate their own police. Not private security, they get to have and train their own police force with law enforcement authority both on and off of company property. This is just a fun fact that I am sure is unrelated to any reason why people might want to travel by private rail.
There can be a lot of privacy and security surrounding private rail cars, which is part of why it's so hard to confirm if fully private passenger rail is going on. Amtrak used to run photography contests. While they've never said, it's believed that the number of people being arrested for taking pictures of trains and rail infrastructure while following both laws and also contest guidelines perfectly is why they stopped. Getting too curious about trains is a good way to wind up in handcuffs.
Train companies run their own trains for fun. They are called Office Car Specials or Business Cars. They have unique livery (paint jobs) and get spotted now and again, often on routes that you can't book via Amtrak. The only video I can find from inside one of these train sets is from 2002, and again, the modern ones have likely been redesigned and refurbished. If you watch that video you will note that the cameraman was more interested in documenting the spec sheets for each car than the nice footage of the interior. Again, I cannot stress how disinterested most railfans are in actual experience of being on a train. I am a bit of a weirdo in railfan circles for caring about the interiors, the views, the menus, etc.
This recent reddit post shows a CSX Office Car in company livery cruising past. If you pause the video at 0:54 you can see that the final car has a window design suggesting a theater seating like set up to provide good views out of the back of the train, which is a giant window.
The ability to travel privately and independent of Amtrak, to have your train prioritized over Amtrak, is for sale. Tour companies do this, and are doing this more every year. But if individual people are arranging fully private, independent travel, there is just no way to know... but it is possible.
So, that is my stab at trying to organize the mess of information I know about private rail travel in modern America. If you are writing fic and want more information on what might be possible, or reference images of high end trains, let me know. There used to private train stations in New York and other places to allow access to passenger rail without even going to a train station. As far as anyone knows, no such station still exists, but they used to!
In short: meetings, parties and leisure travel on private rail cars in the US happens a lot!
My knowledge of historical rail travel is more comprehensive. I have a post here that talks luxury, erosion of class boundaries, crime, etc. I wrote the post as a resource for writers, and also take questions on the topic there.
This is a tricky topic to write about because there are so many types of private / privatized train service in the US. The really juicy high end rail travel is a very insular world. I am going to ignore heritage train service, oddballs like The Grand Canyon Railway, and pretty much focus on three categories:
1) Attached to Amtrak - People who own or rent train cars and pay to have them hauled along behind The Empire Builder or some other route.
2) Chartered Service - This is a broad category. There are a number of passenger train services running under their own power on US rail lines that aren't Amtrak. This category includes a lot of museums and tours.
3) Privileged Access - Very little is known about this tier other than it does exist. In the US, cargo has priority over Amtrak for use of the rails on the vast majority of the system. Amtrak owns a small amount of rail itself, mostly in the Northeast Corridor. But if you make a deal with a rail company like BNSF or are BNSF you can do what you want.
There is a lot of overlap between these categories. It appears that some charter services deal with Amtrak, and some make deals with the large rail companies to get the access and reliability usually afforded only to potatoes, oil and other cargo.
Also, as a side note, Alaska has it's own state-run railroad for passengers, cargo and also charter travel. As far as I know, most of the private travel there is chartered by large tour companies or cruise ship companies. There is no connecting line between the Alaskan Rail Road and the main cargo lines of US and Canada, so most private rail cars can't get up there.
I am going to start out talking about the Attached to Amtrak level of service. These privately owned cars are something like vacation homes. Some people have fancy ones only for themselves and guests, other rent them out when not in use to defray costs. People who do this level of service span both the millionaire and billionaire class.
This level of travel can be very luxe, here is the private train of the owner of Patron Tequila:



Images from this article.
If you want to rent a train car and travel on the back of an Amtrak train, I'd recommend budgeting at least $15k/day. Some of the travel websites out there claim it can starts as low as $12k/day, or even $9k. I think those are lowball numbers that don't include many of the taxes and fees. The cost to supply power to a car attached to an Amtrak train is per day is $2,868.00. That's what it costs just to turn the lights on. In addition to set daily costs, there are also per-mile costs to pull the car.
Technically, the federal government stopped allowing this level of service in 2018, citing things such as 'not meeting revenue goals' and other, well, other BS. Private cars are a money maker for Amtrak, but the company is a very strange political football. It's public transit so Republican lawmakers at the national level want to kill it's revenue streams with fire. City and state Republican lawmakers, governors, etc see it as crucial to their economies. Both very rich and poor Republicans tend to be very attached to Amtrak and see it as important to their lives... and there is a whole political thesis paper that could be written about this. All of my train communities got flooded with disinfo for a solid year leading up to the 2020 election claiming that Biden would end Amtrak... which is insane if you know anything about train funding fights or that Biden has had the nickname of 'Amtrak Joe' for at least a decade and a half.
This political tangent is building to something besides me needing to vent about political disinfo about trains I swear.
The end date for private train cars came and went... with no change in how many were spotted by trains enthusiasts. It's like the large corporations and rich people who like their mobile vacation houses and venues to wine and dine clients basically said 'lol no' and kept on booking per usual. Here is a video from 2019 that clearly shows private cars attached to an Amtrak engine. It's strange that the cars are at the front, rather than the back. This older video shows the more typical configuration. While that is one example, I watched as the groups I am in realized that the ban only existed in theory. Articles came out claiming a 'softened' version of the ban was in effect, but, nope, even those restrictions where clearly not being followed at all.
In short, a bunch of rich people ignored GOP attempts to mess with Amtrak because they found it inconvenient. Rules? Rules are for people with less money.
Obvious disclaimer - People across the entire political spectrum love trains. But there is a lot going on with how the super rich use our rail systems and the GOP's complicated relationship with Amtrak.
Since January 2021, Amtrak now openly allows private cars again and has posted information and prices.
The company that makes the most use of Amtrak for pulling private cars is called Charter Steel. They own five restored vintage cars. I spotted one of their cars while on an Amtrak train, which is what lead me to start looking into private rail travel:

This is the picture in question. It's a hard topic to research, and the company having a name like 'Charter' doesn't help. So many google results about chartered train service instead... Also, it's hard to try to find images on Instagram or search subreddits.
I can find lots and lots of pictures of the outside of the car, but sadly
This image has been posted several times with the claim that this is the Charter Steel's Club Car:

I don't know if it is. Even if this is a picture, it's a very old one. It's possible, likely even, that the interior has been redone done the snap. I've done several deep dives trying to get more info and to this day, that is all I have to show for it. If it's possible to take a picture through the window that clearly shows the inside, well, my camera can't do it at least. And yes, I have tried!
Chartered Service - I'll go over this briefly due to overlaps with Privileged Access.
There are companies you can hire to do custom rail travel and there is regular service on non-Amtrak passenger rail in the US. One benefit to both Chartered Service and Privileged Access is that there's more places you can go.
Amtrak routes:

Cargo rail in both US and Canada:

The vast majority of Amtrak delays are due to other trains getting priority over them on the US rail system. It's not Amtrak's fault, it's just that our rail system puts potatoes over passengers. Amtrak only owns a tiny bit of actual rail, almost all of it is owned by private companies in the US. With some chartered services can get people the higher level of access usually reserved for cargo.
There are people whose hobby is riding Amtrak's The Southwest Chief over and over again hoping for just the right serious delay so they can take pictures of red rock formation in the American Southwest that are incredibly hard to impossible to legally access. Since the start of the Covid-19 pandemic, there has been rising interest in higher end chartered service in the US providing these views in day light. The Rocky Mountaineer is one such service.
Here is a picture of one of their railcars:

For this and most higher end luxury and heritage rail travel, it is so focused on couples that there isn't even an option to book solo.
Privileged Access -
Did you know that railroads are allowed to have their own police forces? With interstate law enforcement authority? Amtrak falls under Federal jurisdiction, but private companies like BNSF get to operate their own police. Not private security, they get to have and train their own police force with law enforcement authority both on and off of company property. This is just a fun fact that I am sure is unrelated to any reason why people might want to travel by private rail.
There can be a lot of privacy and security surrounding private rail cars, which is part of why it's so hard to confirm if fully private passenger rail is going on. Amtrak used to run photography contests. While they've never said, it's believed that the number of people being arrested for taking pictures of trains and rail infrastructure while following both laws and also contest guidelines perfectly is why they stopped. Getting too curious about trains is a good way to wind up in handcuffs.
Train companies run their own trains for fun. They are called Office Car Specials or Business Cars. They have unique livery (paint jobs) and get spotted now and again, often on routes that you can't book via Amtrak. The only video I can find from inside one of these train sets is from 2002, and again, the modern ones have likely been redesigned and refurbished. If you watch that video you will note that the cameraman was more interested in documenting the spec sheets for each car than the nice footage of the interior. Again, I cannot stress how disinterested most railfans are in actual experience of being on a train. I am a bit of a weirdo in railfan circles for caring about the interiors, the views, the menus, etc.
This recent reddit post shows a CSX Office Car in company livery cruising past. If you pause the video at 0:54 you can see that the final car has a window design suggesting a theater seating like set up to provide good views out of the back of the train, which is a giant window.
The ability to travel privately and independent of Amtrak, to have your train prioritized over Amtrak, is for sale. Tour companies do this, and are doing this more every year. But if individual people are arranging fully private, independent travel, there is just no way to know... but it is possible.
So, that is my stab at trying to organize the mess of information I know about private rail travel in modern America. If you are writing fic and want more information on what might be possible, or reference images of high end trains, let me know. There used to private train stations in New York and other places to allow access to passenger rail without even going to a train station. As far as anyone knows, no such station still exists, but they used to!
In short: meetings, parties and leisure travel on private rail cars in the US happens a lot!