I understand Ohm's law quite well thank you.
I also understand that the multi-million ohm resistance is only for pins explictly configured as inputs in code (not an innate protection), headers for pins are clustered together so shorts between nearby can happen under the right (or really wrong), and that depending on the application pins can be defined in an Arduino sketch from INPUT to OUTPUT at any arbitrary point of time. With those three things in mind, in environment where there's vibrations and possible wire abbrasion I like to make sure when possible the signals both comming into and going out of an ATMega are all below 40 mA well before they get to the Arduino board. That way even if an input signal does somehow short to an output pin it doesn't do permanent damage.
However after reviewing my post, I will agree that I was being rather absolutest while making my case and not technically accurate. And since I also failed to mention any of the above mentioned paragraph my initial response also unfairly portrayed Grumpy_Mike as wrong when for defined inputs he was actually correct. The truth is there is no need to make sure an input is under 40 mA, even though I think it can avoid problems, especially within a car. I'll also admit that the for this application it's most likely that the sensors will need to use the analog inputs, and it's rare to use the any pins on port capable of analog input as outputs unless the others are unavailable.
I try to make helpful contributions, but in this case it appears that my reply wasn't helpful. I am sorry I went off half-cocked. 