Standards overviews:
http://www.itsa.org/standards.html -- Overall standards news and discussion page at ITS America
http://www.its-standards.net -- Overall standards links, lists, overviews, and status

ITS National Architecture
The ITS National Architecture is a framework for design and integration of ITS services, spanning a wide area of functionality. It is meant as a higher level complement to some of the more focused standards including the TMDD, ATIS, and other standards.
http://www.iteris.com/itsarch/ -- National ITS Architecture summary and detail

TMDD (Traffic Management Data Dictionary):
The TMDD is geared towards traffic management systems and provides a standardized way to provide traffic information and details including those relevant to public agencies managing traffic.
http://www.ite.org -- The TMDD working page. Click on "Standards" then "TMDD".

RDS-TMC:
RDS-TMC specifies traffic information encoding which is intended for FM data broadcast. It is European based and is being used for an increasing number of North American Telematics systems.
http://nawgits.com/ko_rds.html -- Good RDS North America status overview
http://www.tmcforum.com/technic/compendi/rdsoverv/rdsoverv.htm -- Detailed RDS implementation examples and discussion
http://www.rds.org.uk/rds98/rds98.htm -- See "RDS-TMC" link for general article on RDS-TMC and related standards status

ITIS:
ITIS stands for Intelligent Transportation Information Interchange Systems. It includes an incident/event description list based on and enhanced from RDS-TMC event codes.
http://www.enterprise.prog.org/itis.htm -- ITIS overview
http://www.azfms.com/About/ITSRD/c11.html -- ITIS at Arizona DOT status

ATIS (Advanced Traveler Information Systems):
SAE (Society of Automotive Engineers) have a standard (SAE J2353) which blueprints data structures for traveler information messaging and delivery. It includes everything from user data to traffic data to weather data to parking data and more. Another standard describes location referencing (SAE J1746). These are pay for download.
There is also an effort underway to develop an XML DTD for ATIS data based on SAE J2353.
http://www.sae.org/technicalcommittees/gits.htm -- SAE ITS standards division overview site
http://www.sae.org/servlets/product?PROD_TYP=STD&PARENT_BPA_CD=GV&TECH_CD=ITS -- All SAE ITS standards links
http://www.sae.org/servlets/productDetail?PROD_TYP=STD&PROD_CD=J2353_199910 -- SAE J2353, Data Dictionary for Advanced Traveler Information Systems (ATIS)
http://www.sae.org/servlets/productDetail?PROD_TYP=STD&PROD_CD=J1746_199912 -- SAE J1746, ISP-Vehicle Location Referencing Standard

AMI-C (Automotive Multimedia Interface Collaboration):
http://www.ami-c.org -- Covers in-vehicle multimedia systems architecture

Satellite traffic sensing workshop -- Not a standard, but an interesting technology application review:
http://www.multisat.dlr.de/workshop_0902/ -- Satellite traffic sensing workshop, Germany, Sep 2002