I'm not sure if I'm allowed to ask "essay questions" but here goes:

I've heard about experiments (some conducted in San Diego) where cars
and highways are retrofitted so that the cars can drive themselves.
(Now I'm not speaking about the automatic cruise control technology
that automatically sets a speed that distances you a certain distance
from the car ahead but you have to keep steering. These systems are
currently in some models. But rather I'm talking about a system where
the driver doesnt' have to do anything but sit there.)

Can you give me a brief primer on what the basic technologies are that
are considered for such prototype systems and what the winning
technology is expected to be? Primaarily I'm interested in how the car
is able to discern where the road is.

I don't want a huge amount of detail but some specificity would be
nice. (For instance, if RFID tags are used, how close together are
they, what is the approx range that they have, etc.

A couple hundred words would be preferrable to a long list of
links where I have to fish through reams of engineering speak to find
the info I'd like. I don't have an EE degree but am pretty well versed
in technology  basics. 

Thanks. You guys are great!

I recall experiements with paint sensors from nearly 20 years ago, but
this article says experiments actually date back to 1939.  The roads
would be painted with a stripe that the car can sense.  The following
article seems to me to be for the non-technical reader:

http://www.pcmag.com/article2/0,1759,1130785,00.asp
attention is shifting to vision systems in which two or more in-car
video cameras watch pavement markings and other highway features.

Already, Minnesota has a pilot program that helps snowplows stay
safely on the road in blizzard conditions. Forklifts scoot around
warehouses unassisted, following magnetic floor stripes or
triangulating their positions via video cameras or laser scanners
against wall markings.

Global-positioning receivers and digitized maps exist today, but they
will need to be more accurate. And barely a handful of cars currently
have electronically controlled throttles and brakes. An inertial
sensor (an electronic gyroscope accurate to within a couple of inches)
would be needed when the car is in a tunnel or if a camera is
temporarily blinded.

--outtawork

i remember seeing a news report about that private road that is
retrofitted for self-steering cars.  they way they did it is by
embedding magnets in the middle of the road.  each car can sense the
magnetic field produced by these magnets and follow them.  also, the
magnets are placed either north or south pole up, thus creating a sort
of binary programming language that can be used to tell the cars what
kind of turns/speeds/etc to expect.

cool stuff

Its a very active area of largely dissapointing research! I'd look at
the DARPA web page, and at the Grand Challenge.