We tend to treat our vehicles as junk only when they are no longer able to get back on the road. This should include all those cars still on the road, even though their present condition should not allow them to. This is not something people are ready to do until they no longer can help it. Here is how you know you can no longer run from that fact.
A vehicle that has the lemon status that becomes inoperable qualifies as junk. The lemon law was put in place as protection for consumers where car manufacturers released vehicles that had glaring defects. Therefore, should you find out you have a lemon car in your hands, you shall be compensated with a new vehicle. That lemon can thus be treated as junk. You shall get a good deal when you go to this site.
The mileage of the car shall also tell you whether it has reached junk status. After a certain high number of miles, a car will have lost most its value. Reselling it would not yield as much as you would have hoped. Taking it to a salvage yard would net you more money. The metal parts shall offer you more money, which tells you why it is worth more when treated as junk.
You need to treat a car that needs too many repairs the same way. Such cars take up so much of your money on repairs all the time. You will keep spending most of your money on it until when you finally let it go as junk.
A car that gets written off in an accident also deserves to go down the route of junk. You can take it to a salvage yard and make money off it in cash. There will be parts on it they can use to better effect in another needy car.
Junk cars are also those that are so old they can no longer be put back on the road. You will see some classic cars that are kept in clean conditions, which tend to be highly valuable. This category, however, does not cover that class of cars. We are instead talking about those old cars people still hold on to in their homesteads, even though they will never drive them, and are not looked at as classics. Instead of letting them keep taking up space and rotting away, treating them as junk and selling them off is a better approach.
If ever your car gets to a point where you cannot get much from reselling it, or you have to pay too much money to keep repairing it, then you need to look at it as junk.