Keeping an older modern car running is getting harder than ever - or more precisely, more expensive.

This is one of the few downsides about modern cars - that is, cars with electronics and modern computer controls. They are more reliable and last much longer. But when they reach a certain tipping point - about 12-15 years after they left the factory - the cost to keep them running can quickly exceed the value of the car itself. You're left with an unhappy Catch-22: Pour a lot of money into a car that won't be worth a cent more after you're done. Or don't fix it - and be left holding the keys to an absolutely worthless car.

Here's an example:

You own an early '90s-era Civic or similar econo-car. It's worth maybe $2,000 but still runs fine (modern gas engines routinely run as long as diesels - two or even three hundred thousand miles). One morning, the transmission croaks. If this were a '75 Nova, a brand-new TH350 automatic transmission would cost maybe $600 or so - and a good used one half that or less. Worth doing. But things have changed a lot since '75. Have you priced a new/rebuilt Honda automatic transmission lately? These babies can cost $2,000. Even junkyard ones are pricey.

Who wants to put two grand into a two-grand car?

But without a working transmission, the thing's next to worthless. A parts car; you might get a couple hundred bucks for it as scrap. So its either pour big money into the car just to get back to where you where before - or dig even deeper for an equivalent used car. Or buy a new one and really dig deep.

And then cross your fingers and hope to Crom (the Motor God) that next month the electronically controlled air conditioner head unit doesn't crap out on you. If it does, you're looking at maybe another $800-$1,000 ... or no AC.

So many "little things" can eat you up like a school of frenzied piranhas.

ABS pumps (they can cost more than redoing the entire brake system on a pre-ABS car), electronic control modules (the "ECM," or computer brain that runs your car's engine - and which it won't run without), fuel injection systems that cost more to fix than it used to cost to rebuild an entire engine, $400 a piece catalytic converters and $50 a pop 02 sensors - plus all the other sensors that cover the surface of a modern engine like zits on the cheeks of your teenage kid.

And then there are the air bags. These things may be "safe" - but they are also ticking economic time bombs that can leave you hoofing it (or waiting at the bus stop) at almost any moment.

Take the aforesaid '90s-era economy car. It has two air bags, one each for driver and front seat passenger. Add one relatively minor crash sufficient to trigger the bags - or just one of them.

In the pre air bag days, the car would be fixable, mechanically as well as economically. Replace/repair some damaged sheetmetal and re-paint. No problem. If you used junkyard fenders and so on, it could be done for a few hundred bucks. You could even do much of it yourself - and with basic hand tools.

But air bags are not fixable - and they are anything but cheap. Once deployed, they must be replaced. And not just the bag, but the entire housing they were in - which means the steering wheel and (if the passenger side bag goes off) the entire dashboard. Replacing both bags and the steering wheel/dash can easily run to a couple thousand dollars - before even getting to any crumpled sheetmetal.

Insurance companies will usually "total" a car once the cost to repair it approaches or exceeds 50 percent of its retail value. If you're driving a $2,000 car.... even a $7,000 car - that tipping point is reached pretty easily, even after a fairly minor accident.

This is why modern cars are so much more disposable than the cars of the pre-electronic/pre-computer era. If you're old enough to remember the '70s and '80s, you probably remember routinely seeing cars 20-plus years old still in service as daily drivers. That is much less common today. It is rare to see a car from the '80s - when computer controls and EFI first appeared - still on the road.

One specific example comes to mind: '80s-era Camaros and Firebirds. GM built hundreds of thousands of them. You used to see them everywhere. Now you almost never see them - outside of car shows (and a few redneck backyards). And yet, you still see '70s-era Camaros and Firebirds fairly often, despite their being a decade or more older. Why? The '70s-era cars are simple machines that can be easily and economically kept running. The '80s-era cars are not - and can't be.

What we've arrived at - or are heading toward at a gallop - is the Era of the Disposable Car. It is already implicit; the de facto reality. Tomorrow - or not too far from now - it will be explicit. Maybe even the law.

Cars are becoming more complex - and expensive - at what seems to be a geometric rate of progression. As pressure to make them ever "cleaner" and more "efficient" grows, this trend will only accelerate. A point will be reached - we are very close already - when anything more than routine service, such as fluid and filter changes, may not be worth doing. Either the parts - or the skill needed to do the job - will be too expensive. Cheaper to just throw it away and get a new one.

Doubt it? Think that's extreme? Well, some automakers are already doing just that when it comes to major components such as engines and transmissions. If a problem crops up during the warranty period, they have discovered it's more cost effective to just pluck and toss the part, and replace it with a new one, than it would be to have a $70 per hour tech tear it down, find the problem and fix it.

It is only a matter of time until this inexorable economic logic is applied to the whole car.

Which will mean, as time goes by, that all modern cars will be "disappeared" on a rolling basis, every 12-15 years or so. The only old cars that will survive into their third or fourth decade - as operable machines - will be cars built before the early '80s.

Kind of like "carousel" in the '70s-era sci-fi movie, "Logan's Run." Remember that one? http://www.youtube.com/watch?v=xSnLU9nyFSA No one was allowed to live past the age of 30. When that fateful birthday approached, you went to "carousel" - were lasers dispatched you to the not-so-happy-hunting ground.

But tomorrow's cars may not get to reach their late teens before their time's up.

Such is the price of progress.