traffic answers

Question:  How do the radio stations and TV stations know when there are traffic jams? Are there sensors in the street itself? Do they all go to websites where all of the cameras we see on the signal lights are coordinated and the information goes to one place? Is there one centralized place where all of these people go to for their information? Do they have to call or go to all the different websites?  Is it true what you see on TV or in the movies how people can hack into one place and see cameras all over the city?

Answer:  This is a bigger question than it sounds.  The simple answer is there is a combination of public and private sources of data.  To keep this answer of a manageable size, it is limited to the San Francisco Bay Area.  Similar facilities exist in many other major metropolitan areas as well. 

The Metropolitan Transportation Commission (see www.mtc.org) launched a traveler information system several years back.  It can be accessed either through the Internet at www.511.org or by telephone within the Bay Area by dialing 511.  It primarily collects information fed by sensors in or on the pavement that Caltrans has installed, and formats the information into a useful display map.  There is also lots of transit, accident, and construction information available at the site. 

There are private entities like www.traffic.com, which obtain all the live data from MTC and Caltrans and also install some of their own information collection systems to fill in the gaps or refine the data from 511.org.  Traffic.com also hoped to have information on arterial streets available, but to date there is little displayed because the data is not often collected or readily available. 

There are also well known radio stations such as KCBS or KLIV that have planes or helicopters in the skies and other inputs such as the Phone Force.  KCBS has information available on the Internet at http://www.kcbs.com/pages/11463.php that also show live traffic cams fed from Caltrans. 

The granddaddy of all SF Bay Area sources is the Caltrans Traffic Operations Center, located on Grand Avenue in Oakland, or similar sites in other regions.  They have a website (http://www.video.dot.ca.gov/) where live cameras can be viewed all over the State.  Real time accident information can be found at http://cad.chp.ca.gov/, which is funneled to residents via the California Highway Patrol command center in Vallejo.  Lots of great information is available at http://www.dot.ca.gov/roadsandtraffic.html.   

The cameras you see on traffic signal arms are overwhelmingly most often connected only to the traffic signal controller at the site.  They are used to detect moving vehicles as an alternative to loops cut in the pavement.  There are a few exceptions where the local agency will also transmit the video image to their traffic management center.  Examples include the East Bay Smart Corridors, which display camera images at http://www.smartcorridors.com/accma/, and similar systems in Santa Clara County (see http://www.sccgov.org/portal/site/rda/traffic/).