Passenger trains have different requirements from freight. While there are times when it may make sense to share a line between passenger and freight service, such arrangements are often problematic.
Unless a freight line happens to go somewhere that a direct road doesn't, or unless a particular route has a very high demand, a bus service is apt to provide better efficiency than a train service using freight rails. A passenger train on a dedicated passenger right-of-way may provide better service (which may or may not be worth the cost), but passenger service on shared rights-of-way is often not very good.
One thing that would be neat if it could be done efficiently and practically (though it probably never will be) would be if cars could be *quickly* loaded onto train cars (or even trucks) which could take the cars near their final destination. Given that a train or even truck carrying a bunch of cars uses much less fuel than would those cars individually, this could lead to increased efficiency. Unfortunately, I don't see much way to avoid having the time and expense of loading/unloading/operating these vehicles exceed the cost of simply driving. The only way I can see that something like this might be useful would be if a bunch of people pooled in for a private scheduled service, and the transporting vehicle included a passenger compartment where people could work during their trip. Of course, people who could afford that could probably just as well afford to simply rent a limo.
What is astonishing is that during the Twenties, railroading's golden era, a huge number of passenger and freight trains were hauled on the same track, and the passenger trains tended to run on time.
One thing that would be neat if it could be done efficiently and practically (though it probably never will be) would be if cars could be *quickly* loaded onto train cars (or even trucks) which could take the cars near their final destination.
Amtrak's Auto Train from Lorton, Virginia (near DC) to Sanford, Florida (near Orlando) is an example of this as far as cars are concerned.
Canadian Pacific's Expressway service from Montreal to Detroit is an example of how this is being done for trucks. A good many truck shippers are now working with the Class I's to make this happen on a larger scale. (BNSF has been doing it for J. B. Hunt since 1974.)