Ain’t nobody every jumped a turnstile amirite??!
Turnstiles are just as much an honor system as onboard ticket collectors if you don’t have someone checking over them….and even then, no employee is gonna care to run after the jumpers. Trains systems all over the world are based on this honor system. Vast majority of people are honest and the tickets are so expensive that they make up whatever “loss” they have from jumpers.
For Amtrak and likely most regional rail systems that do on train ticket taking, the number of stations they service exceeds the number of trains. For example, Amtrak runs on the order of 300 trains to service 500 stations. It’s simply more efficient to centralize ticketing to travel with the smaller number of trains than need staff to cover all the stations and e.g. watch for turnstile jumpers (many of which might be little more than just a platform next to a parking lot).
You tend to see turnstiles in higher frequency rail lines, where taking tickets on the train would be too slow to be done between stops or there is a closer match between the number of trains and stations.
On-board ticket collectors are more reliable, in exchange for being slower and costing more. That makes them more worthwhile for services where the fare is large, because recovering a missing fare is more valuable.
Also, turnstiles don’t mix well with luggage, so they are a less attractive solution for long-distance systems. You’re also more likely to have people who aren’t travelling need to get onto the platform for long-distance systems, such as family members helping people to get to the train and see them off. Turnstiles get in the way of that, because they assume that everyone going to the platform is getting onto the train.
Turnstiles are quite an expensive piece of infrastructure. You need the turnstiles, and the ticket validation next to it, and the walls or fences to prevent people from going around, and the gate around the turnstile for people with disability, and the staff to make sure people do not jump over it, etc. It is an accepted cost at a station with tens of thousands of travelers an hour. But long distance train systems do not have that many travelers. And they visit a lot of train stations along the route which would all need the turnstiles installed. That makes it a very expensive system to build and run per passenger.
Trains need conductors. The conductors do not just check the tickets but are responsible for making sure everyone gets on and off the train safely, and operates many of the functions on the train. In the case of an emergency the conductor is leading the evacuation effort and will help the engineer couple to other trains and throw switches if needed. In some stations the Amtrak also have to reverse into the platform which requires that the conductor stands on the back of the train to watch for any obstacles. So a conductor is a legally required member of the train crew even if there is no passengers. Freight trains also have conductors. Checking tickets is something that the conductor does between all his other duties on the train.
Turnstiles are also not the best system and a lot of metro and subway systems are removing them. In addition to being expensive they do slow down the flow of passengers and can be annoying for people with lots of bags or people in wheelchairs. Instead of turnstiles more and more commuter systems rely on random ticket inspections. Even on long distance train journeys you might not get your ticket checked any longer. With assigned seats it is not easy to sneak onto a train without getting noticed.
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