The Pacer "product" was, but it was fundamentally based upon the Leyland National Bus which first went into production in 1972 thus designed from the late 1960's. I was been a tad flippant with the chassis to be fair

however, that said... I'd still rather not ride on a regular basis on a train based upon something original developed to standards from the 60 & 70's
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I'd like to say I'm convinced with that statement but I'm not. The key strength on a pacer would come from the chassis used. That said, the key issues of safety on a pacer and to be fair, any rail carriage of its date are the lack of passive safety built in, the rounded corners, impact deforming fixtures and other such things that have been developed in the 30 years since these things were first built - compare a 80's Ford Escort with a 10's Ford Focus - there's a world of difference in safety inside.
TPWS doesn't make the Pacer any safer, it makes collisions less likely to happen - which is quite a different matter - Whilst the risk of collision may have reduced, the severity of your injuries are influenced by fixtures inside and the overall construction, thus remain at the same level as without TPWS.