Steel ties have been used for many, many years in Europe, Africa, and Asia, anywhere timber was scarce. They've never been common in North America. BC Rail bought a large number of ties from BHP Inc. in the 1980s to used in severely curved territory. The rail seats quickly fatigued (this has been a common problem with steel ties) and when I was on BC Rail last year, there were large piles of steel ties everywhere that had just been removed from track.A couple of companies (including the one you mention) claim to have solved the rail seat fatigue problem, at least for moderate speed application. I believe some of their products are in test in Pueblo.
Plastic ties have also been around for a number of years, having been developed initially for light-rail applications in Europe (I saw my first one in 1985). Primix is just beginning to supply these commercially. Another company, TieTek, is selling large numbers to the UP, after several years of successful testing at Pueblo. The ties are made of recycled plastic, are immune to rot, and offer spike pullout resistance almost as high as oak ties (yes, you just drive spikes into them). These ties may be a cost-effective solution for damp, warm climates and moderate-density rail lines, where rot is the major factor determining tie life. If the technology proves out, this would also be a good choice for light rail lines.
Concrete ties have been used primarily in heavy tonnage/high speed rail lines. Their two disadvantages are that they are heavy and hard to handle, and that a patented and expensive elastic fastening system must be used.
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