I distilled the following from another forum:
See the EMPCommission.org links. The auto testing results are on page 112 of that report. They tested a sample of 37 cars. Here is a summary of the results:
Most cars will not even stall. In a test, where cars were subjected to EMP conditions, they tested both with cars turned ON, and cars turned OFF. I quote "No effects were subsequently observed in those automobiles that were not turned on during EMP exposure." NO EFFECTS FOR CARS THAT WERE TURNED OFF during the EMP, they just started right up.
EMP effects on cars that are running: "The most serious effect observed on running automobiles was that the motors in three cars stopped at field strengths of approximately 30 kV/m or above. In an actual EMP exposure, these vehicles would glide to a stop and require the driver to restart them." In other words, 90% of the cars would not even stall if they were running when an EMP happened. There were some further effects, blinking dashboard lights on some cars, etc.., read the report to see them described. Over 20% of cars experienced NO effects while running, not even burnt out radios, and to reiterate, for the cars that were OFF, there were NO effects.
Here's the conclusion of the commission for trucks: "Of the trucks that were not running during EMP exposure, none were subsequently affected during our test. Thirteen of the 18 trucks exhibited a response while running. Most seriously, three of the truck motors stopped. Two could be restarted immediately, but one required towing to a garage for repair. The other 10 trucks that responded exhibited relatively minor temporary responses that did not require driver intervention to correct. Five of the 18 trucks tested did not exhibit any anomalous response up to field strengths of approximately 50 kV/m."
An EMP could cause some cars to stall, which could definitely lead to accidents when the EMP happens. Most cars will run just fine, we will not likely see a breakdown of our auto transportation system from an
EMP. - SurvivalBlog Editor at Large Michael Z. Williamson