Public transport is almost negligible in Saudi Arabia. As an expatriate, it is really convenient if you have a car of your own.
For those of you with your families, it is almost impossible to survive without a vehicle. The reason is not too far to seek. Women aren't allowed to drive and hence are dependent on their husbands to take them out for shopping, because it is rather not advisable for them to go alone for shopping. This could sometimes be quite a pain, because if your kid is sick or something urgent is required at home, you have to take time off from your work to attend your family. Having a vehicle would come in handy for that rainy day.
If you already have an international driving license before coming to Saudi Arabia, you can skip the first level of driving test. But in any case, it is advisable to go through a driving school in the kingdom before the test rather than giving the test directly, because the chances of your failure are quite high if you give the test without undergoing the driving school lessons. Not that you do not know driving, but that's how the system works here.
Once you have obtained your driving license, the next step is to get a document called 'Istemara', which literally means vehicle registration. You will be given two cards - one which proves that you have registered your vehicle and the other to prove that you are the owner of the vehicle. You must always carry these two cards in your wallet, along with your iqama (residence permit) , vehicle insurance (called 'Ruksa') and driving license. You may be quite surprised that your wallet contains more paper than money!
Never ever, ever drive your car without a vehicle insurance. Usually, if you take your vehicle insurance from a reputed company, you would be given a letter in Arabic which is addressed to the police. The letter simply states that your vehicle is insured and if you show this to the police, you would not be jailed. Hence, you must atleast carry a photocopy of this letter in your vehicle all the time along with a copy of your iqama.
You must keep renewing your istemara once every thre years. However, a pre-requisite for istemara renewal is that you must get your vehicle certified by what is commonly called as 'Computer test' or MVPI (Acronym for Motor Vehicle Periodic Inspection). Your vehicle would be subjected to a series of tests. In 9 out of 10 cases, it would fail the first attempt, so you would have to go back, get the 'fault' corrected and give a re-test. Of course, you have to pay every time you give the test!
By the way, expatriates are not allowed to own pickup vehicles. I would also strongly advice you not to offer lift to unknown people. Also, if you ever travel with your friend's wife, even if it is for dropping the lady nearby, make sure that your friend is also in that car. Despite all your good intentions, it is a crime to do this here. It's no joke, you may be in serious trouble if you do that, because according to the law, it is an offense for an unrelated man and woman to be talking or travelling together.