I have a mini shnauzer. She is adorable, great with kids and not mean spirited at all. However, we do have a problem in the car. She really travels well after the initial excitement wears off, but if we pull in to any parking lot where she knows I am going to get out or if we reach our destination (like a park where I will be walking her) she freaks out. As soon as I go to put the stick shift in park or take my keys out of the ignition she barks furiously and has lately taken to putting her mouth on my arm. She hasn't actually bitten, but she grabs my arm and shakes it like a toy. People walking by have looked concerned. I'm at my witts end. I have tried numerous ways to calm her, but she is relentless. As soon as I'm out of the car, she calms down and waits for me to tell her it's alright to come out. As well, if anyone approaches the car, even people she knows well, she goes ballistic at the window. She sounds ferocious. Friends of mine have taken to calling her "killer".  I do not know what to do to correct this behavior. Help please.... Pamela

It's just over excitement (and barking at the window is guarding her personal space) and the very simple way to sort it (and to travel safer) is to always use a cage for travelling. It's really not safe in any way to travel in a vehicle with a loose dog.

Ditto, have her in a crate, as well as safer, less room for her to wind herself up with excitement, can even be covered if you wish (and it's not to warm). 

You can also then stay in the car until she calms down, so that exits are when she is calm.

Ditto

As well as the restraining her as above. When she gets over excited when you put the stick shift in park or take your keys out of the ignition id just sit still arms folded ignoring her until she calms down however long it takes. As if you react or carry on getting ready to get out of the car it will just make her more excited. once calm tell her good girl then get out. She will lurn that barking at you and mouthing you wont get her anything but staying calm gets her out where she wants to be.

Luckily all my dog's reacted well in car although we always used a harness, rear guard or crate dependant on make/size of car we had at the time. Not a keen fan on dogs loose in car as anything animals, humans when brake gets slammed on at speed becomes a heavy dangerous force if not harnessed or wearing a seat belt. I see many a dog sitting in a car with the top down roaming between the seats! What if the dog suddenly lept out? Or had a go at a cyclist?
Maybe time just spent getting in car, in crate, running engine then just get out? Then move on to just going round block, a treat then slowly extending distances to get used to create or seat belt harness extension?

Haven't read your answers so this may have been suggested already, but CRATE her.   It's far safer to travel with a dog in a crate in any case.

Yes as others have said you need to crate her, safer for her and stops her getting to your arm. Then you just teach her to sit quietly while you open the door and put her lead on. It won't stop her barking at people who approach the car, that's guarding her territory and many dogs do it.

Re: Scoutmaster and barking and attacking in the car. Thankyou so much everyone for your insights. There was an overwhelming concensus that she should be crated. Although this will probably be an adjustment for her, I've thought about this as well and I know it would make for a safer ride for her. I will try it. Thanks again, Pamela