Office of Operations
21st Century Operations Using 21st Century Technologies
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Appendix B. Analyzing Sign Data

FDOT archived the activity logs from the software it uses to manage messages on roadside signs for the period from July 29, 2005 through July 24, 2007. This software polled the signs at roughly 2-minute intervals, and the signs were expected to respond with the message currently displayed on the sign. The Evaluation Team analyzed these logs to assess FDOT's usage of the message sign network.

For each sign, the logs were reviewed and one of three status codes to each sign for each period of time:

  • A status code of Message indicated that the sign reported back the currently displayed message.
  • A status code of Connection Error indicated the sign management software reported an error connecting to the sign.
  • A status code of Unknown indicates that the sign did not report status information for a period of 12-minutes or longer.

When a sign message was present, the Evaluation Team went on to review each message, identify the type of message that was displayed, and parse the content of the message to identify key characteristics of the message. The messages were parsed by compiling a list of formats that were used on FDOT signs. Each format included both text that must be included in a sign message and parameters that could be set within the message.

For example, the message format

"CONGESTION / AHEAD <DistanceTo> / EXPECT DELAYS / CONGESTION / <LocationFrom> TO / <LocationTo>"

would match any sign message that began with the words "congestion / ahead ", followed by any text that represented a distance (e.g., "3 miles"), followed by the words "/ expect delays / congestion /", followed by any text recognized as a location (e.g., "SR 436"), etc.

Associated with each message format would be one of the following message types:

  • Blank, indicating that the sign was blank.
  • Test, indicating that a test message was being displayed.
  • Advertisement, indicating that a traffic-related "advertisement", such as "For Traveler Information Call 511" or "Buckle Up," was being displayed.
  • Information, indicating that information about a local event or attraction was being displayed.
  • Exit Information, indicating that an exit number was being displayed. (This message type was used for custom signs used to suggest the best exit to take to reach specific local attractions.)
  • Travel Time, indicating that travel time information from the sign's location to a location ahead was being displayed.
  • Diversion, indicating that travel time information for two alternate routes to the same location was being displayed.
  • Congestion, indicating that a warning of congestion ahead was being displayed.
  • Crash, indicating that information about a crash ahead was being displayed.
  • Road Construction, indicating that information about upcoming road construction was being displayed.
  • Other Incident, indicating that the information about some other type of incident (i.e., not a crash, road construction, or congestion) was being displayed.
  • Future Incident, indicating that information about a future incident, typically planned road construction, was being displayed.
  • Road Closure, indicating information about a road closure ahead was being displayed.
  • Detour, indicating information about a detour ahead was being displayed.
  • Speed Limit, indicating that a speed limit was being displayed on a VSL sign.
  • Amber Alert, indicating that an Amber Alert message was being displayed.
  • Law Enforcement, indicating that a message related to law enforcement efforts (e.g., "Look for car / Tag #### / Call 911") was being displayed.

Matching a sign message to its format allowed assigning that sign message to one of these message types. It also allowed for the key parameters in the sign message to be parsed out of the message. In the above example, three parameters would be parsed out:

  • The DistanceTo value, which would be converted into a numeric value indicating the distance from the sign to the position where the congestion began.
  • The LocationFrom, which would be converted into an integer that identified which item in a list of recognized locations was the location where the congestion began.
  • The LocationTo, which would be converted into an integer that identified which item in a list of recognized locations was the location where the congestion ended.

The following list is describes the parameters that could be included in a sign message:

  • Distance From, which was the distance to the start of the incident being described by the phrase.
  • Distance To, which was the distance to the end of the incident being described by the phrase.
  • Location From, which was a cross-street name indicating the location for the start of the incident being described by the phrase.
  • Location To, which was a cross-street name indicating the location for the end of the incident being described by the phrase.
  • Delay From, which was the minimum travel delay associated with the incident being described by the phrase.
  • Delay To, which was the maximum travel delay associated with the incident being described by the phrase.
  • Travel Time From, which was the minimum travel time associated with the incident being described by the phrase.
  • Travel Time To, which was the maximum travel time associated with the incident being described by the phrase.
  • Road Blockage, which was information about a road or lane blockage caused by the incident being described by the phrase.
  • Speed, which was a speed limit for a VSL sign.
  • On Road, which was the road on which the incident being described by the phrase occurred.

The above approach worked for many sign messages. However, some sign messages contained multiple types of information (e.g., a message about a crash may also contain information about congestion caused by the crash). In these cases, each message format was divided into a series of phrases with a phrase type and parameters identified for each phrase.

For example, the message:

"SR 528 / 4 Miles / 5 Min / SR 50 / 16 Miles / 22 Min"

would be assigned the Travel Time message type and parsed into two Travel Time phrases. Each phrase was parsed to identify the Location To (e.g., "SR 528), the Distance To (e.g., "4 Miles"), and the Travel Time From (e.g., "5 Min").

Each of these pieces of information was coded and saved in a database for further analysis, along with an identifier for the sign that held the message and the date and time at which the indicated message was first displayed and when it was replaced with a different message. The result was a database that had converted the text message on each sign into a set of numeric values that could be analyzed to gather information about how FDOT used its signs.