Do accompany the agent during the enumeration of scrapes and dents and keep a copy certifying the initial condition of the car. The road system is built to familiar US standards. Drivers are macho, impatient, and indecisive. On the secondary roads, you can easily get sidetracked by following a straight line instead of the good pavement. PR-14 between Aibonito and Coamo is twisty and unmarked for so long that I needed to stop and ask whether I was still on it.
Speeds are in mph but distances and exit numbers are by kilometer.
Maps are all a little out of date. The biggest disappointment is that Puerto Rico lacks the US system of motels at expressway exits. The government inspects them and regulates the use of this term. There are bargains, but they aren't on the Internet or in the travel agent's catalog. The air conditioner, run all night, blocks out most of the street noise.