how do i teach my 3 1/2 old Aussie not to chase cars!?

A leash or a fence would keep her safe. If you do not insure her safety you will be on here next, "my dog was hit by a car" These "stupid opinions" are from people that know how to keep their dogs safe and are willing to do so.

" i WILL not put her on a leash or behind a fence as i think it is mean and unnecessary thing to do."

Then you're going to have one dead dog.

If you want to let her run around, you need to find a SAFE place for her to do so. I've never let puppies -- ever -- run around in my yard near the road; their off-leash experiences are limited to up near the barn and in the pasture until they can be trusted to come when they are called and not foolishly run off towards the road.

Put her on a leash in the yard or get her a fence. Those are your realistic options; she wants to chase because she's a herding dog and these are fast moving objects - to her, they look like fun!

You can try to correct her but ultimately she'll probably never be 100% and I personally don't like to take any chances with my own dogs.

She should be on a leash. if you insist on letting her roam free ( which #1 could get you a ticket due to 'leash law' in most states and #2 isn't very smart if you live next to a busy street) you should at least keep on a leash until shes reached an age to where the excitement has worn off while she is outside. But Australian shepards are protective over their homes and this could be her way of trying to chase the cars off. Also they are working dogs used on ranches to herd cattle and other livestock so it is their Instinct to chase...Also when dogs are in the wild they do not tend to live near streets where cars are going by to cause danger. A DOMESTIC DOG IS WHAT YOU HAVE NOT A WILD DOG!!! If your too lazy to WALK your dog for exercize or cant afford a fence you shouldnt have one. your dog is NOT meant to be running free and it is not MEAN to have a fence or leash!!! what is mean is your dog chasing a car and getting run over which will be your fault. DOGS ARE NOT AWARE OF THE CONSEQUENCES OF DANGERS OF A CAR!!! ITS YOUR RESPONSIBILITY AS A DOMESTIC DOG OWNER TO KEEP YOUR DOG SAFE AND OBVIOUSLY YOU DONT KNOW HOW WHICH IS WHY YOUR ASKING US! we arent trying to be rude we are just telling you what is best for your dog

Fence or leash. She is a herding dog and her every instinct and inclination is to chase things that move. If you want her to live, you will leash and confine her so that instinct doesn't kill her.

If you are a good trainer, you can get to the point where she will remain under command and hold a stay or turn and come when called when a car goes past, but it is highly unlikely that you will ever be able to undermine her instincts enough to actually stop the behavior when she is not under direct command.

You keep her safely behind a fence or on leash, like other responsible dog owners do. This IS a herding dog, her instinct is to chase.

Teach her a solid recall. And don't give her to opportunity to chase them. Keep her on a leash, or safely behind a fence.

Great solution for that. Leash.

by keeping her on a leash...........just that easy............. YUP WE ARE RESPONSIBLE .......AND YOUR NOT RESPONSIBLE DONT LIKE HEARING IT THEN REMOVE YOUR QUESTION