Hi Cornelia
No, all insurance agreements are most certainly not standardised. I've looked into this in great detail for our car rental articles and it proved impossible to compare the prices/value being provided by different rental firms becuase of the insurance issue.
By law, all vehicles must carry third party insurance. In other words, they protect any other vehicle/person/property hit by your vehicle. It does not cover the costs of repair or recovery to your own (private/rental) vehicle.
These most basic policies give you, the hirer, no protection whatsoever. However, some rental companies have better insurance cover and some (but not all) provide a cap on how much you might have to pay in the event of an accident or damage. The Yes Tourism site has proved an invaluable source of information here.
I see that normal vehicles hired from Auto Rentals have a limit of TT$7,000 (US$1140). KCNN have a limit of US$600; Sheppy's (our favourite) US$650; Shermans US$1140. Thrifty have no limit.
Now, over an above this basic cover which is included in the advertised rental price, you can buy additional insurance cover called Collision Damage Waver (CDW). For an extra sum of anything beteen US$4 per day and $20 per day, you can buy various levels of cover that limit your liability, in the event of an accident or damage of your own making, from various levels between a very helpful Zero, to sums lower than the basic limits above.
As you see, it's a nightmare of complexity. Readers should remember that the cost may not be simply the cost of repairing a vehicle if you damage it. There could be vehicle recovery costs and also, potentially, damages for the loss of income while the vehicle is off the road being repaired and unavailable for rental. Remember, also, that "off-roading" is not covered by any insurance policy. So, if the suspension on that old Suzuki breaks while you are trundling down an unmade track to a remote beach, you could be in for a BIG bill.
Wake up - you're not concentrating.
