Two passenger cars have been instrumented for a comparative study of vehicle micro environments (data gathered from onboard vehicle sensors) and the macro environment (data gathered from a Detroit metro area weather station). Environmental sensors were installed at more than thirty corrosion prone sites on each of the two vehicles to measure temperature and relative humidity of the air and temperature and time-of-wetness of the surface. The weather station data include temperature, relative humidity, and daily rainfall. Data collected over a one year period are analyzed and the results are presented. The results indicate that the micro environment (or “environmental corrosion load”) varies considerably from site to site around the vehicles. These vehicles will continue to gather data for another year. They will then be sent through several cycles of a total vehicle corrosion test at an automotive proving ground. The micro environment response during the test will also be recorded. These data will then be combined with the results of corrosion acceleration factor studies in laboratory environmental chambers. The goal is to estimate local site acceleration factors within a vehicle in proving ground tests relative to actual field conditions. This will lead to more meaningful pass/fail criteria for these tests. In addition, the results will be used to predict the micro corrosion environments within vehicles in any global market based on macro environment (weather bureau) data from there.