All foreign vehicles entering US territory must meet minimum US safety standards. Such vehicles must be registered annually with US authorities to receive the proper approval. The same regulations and penalties should apply to foreign vehicles as apply to domestic vehicles, and the fees charged should cover all costs related to enforcement. Major safety concerns should result in grounding, but minor concerns should be fined sufficiently, varying based on their severity.
The fines for vehicle pollution should use the same regulations and penalties in effect for domestic vehicles, namely a fine for each unit of pollution of each type emitted. Perhaps odometer readings, hours of run time, or other measures could be taken both while entering and exiting the country to determine the total cost for such fines.