In response to urban.turban's query, here's what you need to do to get a Causeway toll card. This will enable you to use the "Authorised personnel only" toll lane which is usually easier than the other lanes. On a bad day though, they use this as overflow so it won't usually help you then. It also gives you a 15% discount on the toll fees.
First, you need a bank account in Saudi with a debit/credit card. You can pay in cash but it involves an extra step which is definitely less convenient. You'll also need your iqama the first time you do this to actually get the card and to be able to pay at least SAR850.
The office you need to go to is usually open Sunday-Thursday only between the hours of 8:30 and 2pm. This might change, e.g. during Ramadan. It might be possible that it's closed for an hour for lunch although I get there first thing (my recommendation) so don't know about this. Don't forget prayer times too.
The office is on the Saudi side (so you need to plan to do a u-turn and cope with causeway traffic both ways if you are coming from Bahrain). From Bahrain, do all the Saudi procedures and turn left after the Costa coffee booth. The office is then on your right. There's a male and a female entrance. If you take your wife with an iqama, she might be able to get it done quicker. Who knows?
You'll get a number and you wait your turn. This can take 30+ minutes or even longer at busy times so bring a book or candy crush saga or whatever.
When your number comes up, tell them you want to get a card if it's your first time. They'll ask for your ID and process a new card for you. You'll be required to pay SAR850 in a card machine. You can only pay in SAR850 chunks. So, you pay SAR850, SAR1700, etc. It's up to you.
If your card doesn't work or you only have cash, they'll give you a piece of paper and direct you to go over to the bank near Kudu. They can't take cash so they'll ask you to pay it into the bank there, get a receipt and bring it back to them. The only good news about this is that you don't have to queue up again when you get back to the office. Just go to the front and they'll make some poor guy wait for you to finish your business.
The procedure to top up is exactly the same as getting the card for the first time except you don't need your ID. This means you can top up your own card plus a friend's if you want which I've done before and him for me.
After you've topped the card up, you can ask them how many trips it's valid for to work out when you need to come back. I always keep a little in reserve. Some guys just wait until it runs out and then go back when the card no longer works.
To use the card, just present it to the little brown box just to the left of the cash window at any toll booth (not just the authorised one). You'll hear a beep and the barrier will come up. Don't rush this. Sometimes it beeps and the light stays red if you're too hasty after the previous driver. I reckon you get charged for nothing when that happens, but I could be wrong.
As with all red tape in Saudi, any of this could change at any time so bear that in mind before you shoot the messenger.