No, it is not open to the public. Not only are there the usual concerns about safety around railroads -- multiplied by the fact that equipment is often subjected to unusual stresses which could result in catastrophic failures -- but the test center also does work for specific rolling stock manufacturers. The equipment sent there for testing is often pre-production and has not even been announced yet. So, there's a fair amount of concern about people seeing proprietary designs before they become available -- or of people seeing flaws in pre-production equipment, which would be fixed by the time the equipment goes into normal production.

(I corresponded with an official of of the test center a number of years ago about the possibility of doing photography there or doing a feature about the center -- and was given the above-cited reasons for being turned down.)

Yes, members of the press are sometimes invited to the site for specific events -- but are only given access to parts of the site.

I also got the impression that it might have been possible to arrange a visit (as a journalist) if I was open to a wide range of dates and the visit could be scheduled at their convenience at a time when no proprietary equipment was there. However, I had asked about possibly visiting the site during a specific time when I was already going to be in Colorado for other purposes. And, making a trip to Colorado from the East Coast just for that purpose would have been too expensive for the anticipated return from that visit.

-- Ernest