There are a number of applications for RFID being developed for access control.  The fastest growing are for personnel access, gate control, and parking facilities.  Here's a brief look at each of these applications.

Personnel Access
In its most common form, RFID access for personnel may simply be the inclusion of an RFID tag in the identification badge of the worker.  RFID has made inroads into this area that was originally dominated by the magnetic stripe badge.  RFID applications for personnel access typically uses low frequency, 135 KHz, systems for the badge detection.
 
RFID badges can be used to control access to particular areas, for time keeping, or other applications.  For example, there are two popular medical applications that move into the higher frequency domain where the application is used to determine the location of either medical staff or wandering patients.
 
Gate Control 
There are two primary areas where RFID is used in gate control: gated communities, and industrial facility access.  In both applications the RFID system is frequently used in conjunction with electronic loop detectors to control the time the gate is open or to control the closing of the gate once the vehicle has cleared.
 
Many gated communities have exchanged the cost of the 24-hour gate keeper for an automated system employing RFID.   This way the gated community has only the expense of the reader and loops to implement RFID technology.
 
Switching to RFID is more popular in areas that have toll roads or other systems that employ tags already.  Even in more isolated communities, the implementation of the RFID may be cost justified.  The more common systems are implemented using either windshield tags or license plate tags for the vehicles.
 
For industrial facility access, visitors or commercial vehicles will typically employ a telephone that may be used to request entry.  Depending on the style and number of gates (one or two) vehicles exiting the community may not require RFID tags to energize the exit gate, simply loop control.
 
Some trucking companies are also implementing RFID as a gate control method.  In many of these installations the RFID is also used to verify load matches, tractor to trailer or tractor to container.  As noted in this article about RFID in transportation, other information may be captured by the RFID system, such as fuel level, odometer reading, etc., depending on the type of tags being employed.
 
Parking Facilities 
In areas or businesses that have other applications for the use of RFID, parking facilities may be able to take advantage of the RFID infrastructure to improve customer service.  Airport administrators, for example, have found that when implementing RFID for curb space tracking and control, the application may be extended into their parking facilities through the installation of card readers at the entrance and exit points.  Such implementation provides the customer faster ingress and egress from the facility. 
 
Even when the parking facility is not associated with a business such as an airport, the investment for tags can be a worthwhile investment to improve customer satisfaction.