98 elantra car, lifters are rattling, is the car safe to drive? should I be concern ?

Yes, you can pick up engine treatments at your local auto parts store or at wal mart. I would be concerned with the lifters making noise if the noise does not quiet down or go away after the car is warmed up. My truck was the same way, the lifters clattered until the engine was fully warmed up and on real cold days it was annoying. It could be the start of a major problem so be prepared to get a backyard mechanic to work on it, do it yourself or pay a shop to do it. This problem usually can be fixed by changing the lifters. If you are going to do something major like this it is just better to completely rebuild the engine including sending the engine to a shop to be machined.

The problem is caused by the oil ports getting clogged or that the ports are too small when the engine was manufactured. The clattering is starvation of oil. Another good cure for this is to use a synthetic oil because it does not return to the oil pan as fast and it aids to reduce the wear that is caused when cold starting the engine. Even in a warmer climate synthetic oil lubricated better then a conventional 10w30 oil. Try mobil 1 full synthetic and an engine treatment from lucas oil.

This is a touchy answer.

If the lifters are rattling due to a little wear, use 15W-40 Rottela T diesel oil in it. Provided you are not in the north where it gets very cold. Rottela is a very high quality oil and very good at quieting noisy valves. I have run it in a Miata sports car with extremely good results.

If it is from very high mileage, valve train/or bearings are just showing their age and telling you that they are about to pass on.

Given the age of the car, it might be better to change the oil and drive it till it blows rather than to try get it repaired. You can get a newer car for less than an engine overhall these days if you look.

As others before me have mentioned, there are more car accidents per year resulting in injuries or worse than the same for aviation incidents. The only difference is there will be generally a higher loss of life in an aviation incident if say a 747 or an A380 crashed for example. The figures produced by incidents like these often make people think that air travel is more dangerous but accidents that actually harm people happen so much less than they do in a car. Car accidents happen everyday across the world in may numbers but air accidents do not. Drivers of motor vehicles on the road are less regulated than pilots and have no checks performed on them compared to pilots which have many especially those that fly for an airline. You could get into a car under the influence of drugs or alcohol (Usually illegal and definitely not recommended) and crash and die with people with you but airline pilots are generally sensible and have a copilot with them that would relieve them if they believe they are incompetent to fly. If I had the money then I'd fly by air every day because it is safer.