The other thing to be aware of is not just a traffic busy area but a very rural area.

If you live in one, coyotes and cougars can kill your pets.

Have a cat door if that is the case--make sure your pet has an easy in if it gets frightened. I also had an indoor/outdoor cat in unincorporated King County (Seattle/Renton area). She was a healthy 12-13 when we moved to an apartment in the Seattle UDistrict--her health actually went down then as she only wanted to stay indoors (she was unaccustomed to the louds sounds of the city and all the people (in an apartment complex). She lost interest in being active.

You will have to make sure you have shots up to date--including FIP. You will need to watch for worms and even minor injuries or bites that could get infected.

Just no there are risks and weigh that in. Also you should consider how "streetwise" your cat is. A cat who has been sheltered inside since kittenhood is much more likely to get hurt than one who has adapted it's behavior to being outside.

<I think the "average lifespan of an outdoor kitty being less than 3 years" must apply to outdoor only/feral kitties. >
It's an average, so there will be some that live longer and some that live shorter lives.

I grew up with indoor/outdoor cats. They usually only lived about 5 or 6 years. I have friends who had indoor/outdoor cats and they lost cats every other year. Also if your cat gets injured or sick outside, you are less likely to see them and respond to their illness/sickness. I don't live on a busy street, but I have seen more than my share of dead neighbor cats in the road. It's heartbreaking.

Also take into account local wildlife. Cats are NOT native species in North America. They decimate populations of native birds and small mammals, some of which are already threatened.

I suppose I should say that in my whole cat history (which is like 30 years now), my cats have always been allowed out and in, but I've been very careful to always live in a place that will in a quiet neighborhood or will be far from any kind of road or dangerous situation for them. I don't move much, hehehehe. Still, in a quiet neighborhood my neighbor backed into my cat (he lived, but rather dinged), and in a rural neighborhood another cat was hit by a speeding car that then itself crashed (served them right) and he was killed immediately. And where I live now, a third cat was carried off by a large wild animal and the cat was just sitting on our front porch minding his own business.

Strangely, that particular cat, Nelson, suffered from many terrible injuries (which he caused himself, various ways) and illnesses during the whole time I had him; I've never nursed a cat so much and so long for all kinds of things; he was a one-kitty cat hospital really and eventually the vets and I came to believe that he was simply indestructible. He was always pulling off all kinds of amazing fast healings and turnarounds. Yet, in one moment, only a few feet away from me at dusk, he was gone. I found his skull a few months later in the back meadow and I have it on my altar.

Outside of the two who died, all of my other umpteen cats have lived into their teens and died of such things as cancer and kidney failure. And they were all indoor/outdoor. My oldest cat now, she's 16, always seemed healthier than everyone else and basically refused to come in at all except to eat for the first 14 years of her life. Now she's a homebody, though, and stays in the house and on the deck.