One of the major barriers to bringing a foreign car into this country is having a the appropriate crash testing done for the NHTSA. It looks like VW had the Polo and Lupo crash tested for the US market and the information is on file with the NHTSA.
VW Polo report
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Photos
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VW Lupo report
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Mercedes A class report
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Audi A2 report
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Suzuki Wagon R
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You can search the rest of the data base here.
Query on Vehicle Database based on selected Test table parameters
Obviously theres still the matter of emissions compliance with the EPA.