Regarding the robbery and stealing, the peninsula Yucatan seems still
a kind of paradise and there is a lot less crime compared with other
cities, inside and outside of Mexico.
However, I would rather go by bus instead of the hassle with street
bumpers, police and finding myself all of a sudden in an area, I would
rather see in a movie then in real life. I found some information
about the Cancun area at a page called queondamex but it seems as if
the street description there is basicaly restricted to Cancun.
Going further south or west by car, I would not leave the highway. The
highway is in good condition, the other streets are not.
One good thing is that it is hard to get lost. There are traffic signs
all over and just going straight ahead leads inevitably to the next
information.
But as I wrote before, I would prefer the bus. These ADO-Busses are
with tv and air-conditioning and I travel relaxed.