RSRP difference between in outdoor and inCar

i need help to find a document that mentions RSRP difference between Outdoor and incar.

I don't have any documents but this is something hard to compare with because the serving cell may be in front of your car or behind your car that may give you a different result. I would say typically it's about 3- 5 dB difference. It's better to get TEMS phone or equivalent to do an outdoor walk then do a test drive when you hold the phone in your car with all windows up.

Thanks for your answer, :)