To take some doubt away: http://www.sciencedaily.com/releases/2012/06/120607141644.ht...

I don't doubt there are all kinds of new materials out there stronger than steel, but the article clearly states that he uses "ABS plastic via Fused Deposition Modeling", which is a different material and a different process.

ABS plastic is a very common hard plastic. Its the stuff used in Lego bricks [1], for instance.

[1] http://en.wikipedia.org/wiki/Acrylonitrile_butadiene_styrene

So treading on the car in bare feet is definitely a no-no, but that doesn't particularly support the stronger than steel claim.

ABS is not even close to steel, especially good steel.

                               | ABS   | Steel
    ---------------------------+-------+------------------
    Compressive strength (PSI) | 6,750 | 16,000 - 70,000
    Tensile Strength (PSI)     | 6,500 | 36,000 - 115,000 (for stress-proof steel)

http://www.machinist-materials.com/comparison_table_for_plas...

I believe that there are UV-resistant (sunlight) treatments for ABS. Many polymers (plastics) are vulnerable to UV light, but are still used in outdoor environments without major ill effects.

And yes, my earlier implication was that it is less strong than steel. A strength-strength comparison is probably not fair here as ABS would be considerably lighter. Even still, steel would be approximately 10X the strength, with about 7-8X the density. A further issue is that 3D printed ABS would not be as strong as bulk-material ABS, although I am told this is improving.

From that same page: >ABS plastic is damaged by sunlight. This caused one of the most widespread and expensive automobile recalls in US history.

Speaking of plastic cars here is some history: http://en.wikipedia.org/wiki/Duroplast