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San Antonio Area Freeway System

This page last updated October 14, 2014

TransGuide is San Antonio's inter-agency Advanced Transportation Management System.  When it went online in July 1995, it was the first system of its kind in the nation and it continues to be a leader in Intelligent Transportation Systems (ITS) technology.  Now operational on about 100 miles of freeway, the system may eventually cover almost 300 miles of freeway in the San Antonio area.

Below is a map of TransGuide's current coverage area.

TransGuide coverage map

The original 26 mile section consisting of the freeways around downtown went online on July 26th, 1995.  The sections on US 281 north of St. Mary's, Loop 410 west of I-10, and I-10 between Fulton and Wurzbach went online in early 1999.  The sections on I-10 north of Wurzbach, Loop 1604, and Loop 410 east of I-10 went online in August 1999.  The section on I-35 between New Braunfels Ave. and Walzem went online in March 2000, and the section between Walzem and Starlight Terrace went online in August 2000.  The US 90 segment, west of Zarzamora, went online in June 2001.  The section on I-37 near Loop 410 went online in May, 2002.  The segment on I-35 north of Starlight Terrace and on Loop 1604 west of I-10 was completed in April 2003.  The section on US 281 from Basse to Nakoma and on Loop 410 from Ingram to Culebra were completed in 2009.  Coverage of US 281 north of Nakoma to Winding Way was completed in 2012.

TransGuide equipment will be added to Loop 1604 from Bandera to Culebra as part of the project to upgrade that stretch to an expressway.  TransGuide cameras have been added to a couple of locations outside of the fully-instrumented sections including at the SH 151/Loop 410 interchange and at I-10 East at Loop 1604.  Additional cameras are currently being added to Loop 1604 between NW Military and Blanco.

In 2006, TransGuide was designated as the central TxDOT unit to handle statewide Amber Alerts and other emergency alerts.

In 2008 in coordination with TxDOT's Austin district, ITS coverage was extended to the entire I-35/San Antonio-Austin corridor.

In November 2009, TransGuide upgraded their website and internal computer systems and announced a maintenance program to clear a backlog of deferred repairs and upgrades to field equipment.

System components

TransGuide uses various technologies to detect incidents and warn motorists.  The system is composed of the following major components:

  • Dedicated divergently-routed fiber-optic rings and associated communications equipment
  • Over 2,500 inductive loop, acoustic, radar, or video-recognition (VIVDS) traffic detectors at 220 total locations
  • 185 closed-circuit, remote-controlled video cameras
  • 230 mainlane and frontage road Dynamic Message Signs (DMS)
  • 246 Lane Control Signal (LCS) systems (currently switched-off due to maintenance funding limitations)
  • Three-story Traffic Operations Center (TOC)
  • Distributed computer system, specialized software, and related equipment

The TOC is located in the southwest corner of the I-10/Loop 410 interchange on the northwest side.  In addition to TxDOT, the San Antonio police, fire, and EMS dispatchers are located at the TOC, as well as dispatchers for VIA Metropolitan Transit.  This allows seamless coordination with these agencies during major traffic incidents.  In 2009, the City of San Antonio established their own Traffic Management Center in the TOC from which they manage the city's 1,200 traffic signals.

How it works

The system is designed to locate incidents within two minutes and then warn motorists within 15 seconds.  Here is how it works:

  1. The traffic detectors located in each lane at mile intervals measure traffic volume and speed in 20-second rolling averages.  When a sudden or unusual change in volume or speed is detected, the system alerts personnel at the TOC.
  2. Upon receiving an alarm, operators activate the nearest camera to determine the cause of the alarm.  The operator enters information about the incident (type of incident, lanes obstructed, and traffic data) into the system which then searches through a database of over 30,000 scenarios and selects a corresponding response plan based on the situation.  Police and fire dispatchers located at the TOC also use the cameras to determine which emergency services to dispatch. 
  3. This response recommends what changes should be made to DMSs, LCSs, and other equipment.  These changes are presented to the operator for review and, upon approval, the system executes all the changes within 15 seconds.  TransGuide can also change the timing of traffic signals along the access roads and major surface arteries if traffic is forced to divert because of a freeway closure.

DMSs give text-based messages alerting drivers to incidents or congestion ahead or on an intersecting freeway.  LCSs display one of the following symbols to guide motorists into the appropriate lanes:

This lane or ramp is open to traffic

There is a hazard on a shoulder adjacent to this lane or this ramp has a hazard or congestion ahead; this symbol may soon be used to warn of congestion ahead on freeway mainlanes

This lane is closed ahead and traffic should merge in the direction indicated
This lane or ramp is closed

Obeying these signals is important.  Failure to do so causes increased congestion at best and additional accidents at worst.  Also, state law requires motorists to obey them.  A survey in 2007 showed about 80% compliance with LCS and DMS messages.

(Note: In late 2009, the decision was made to turn off the LCS system as a cost-cutting measure.  Maintenance on the signals had been deferred due to financial constraints for several years and it was determined that there simply was not sufficient funding in the foreseeable to restore and maintain the signals.  If funding is available in the future, the system may be restored.)


Through the years, several studies have proven TransGuide's benefits to San Antonio motorists in the form of reduced secondary collisions, mitigated congestion due to expedited incident clearing and driver information, and, most importantly, lives saved.  Here are some statistics from one report that did a before-and-after study of the first phase of TransGuide:

  • 41% reduction in crashes
  • 20% reduction in response times to incidents
  • Annual savings of $1.65 million in time and fuel
  • 2,600 gallon fuel savings per major incident
  • Increase in driver compliance to posted instructions from 33% to 80%

(Source: US Department of Transportation Study, 1997)

The future

TransGuide has been a leading innovator in the ITS field for over a decade.  In the future, TransGuide will continue to develop and implement new technologies to improve traffic management.  Besides continued physical expansion of the system, other plans for TransGuide are:

  • Toll system integration: TransGuide will be fully integrated with San Antonio's proposed tollway system.  For example, TransGuide would display travel time comparisons between tolled and non-tolled lanes to help drivers make informed decisions on the best route to take.
  • 511 service:  TransGuide is planning to implement a local 511 telephone traffic information service.  511 is the national standard telephone number for such services.
  • Highway Advisory Radio: These special radio stations broadcast information about localized traffic conditions and will be especially helpful for through trucks on the I-10 and I-35 corridors.
  • Interregional communication: With most major metro areas in Texas now fielding ITS systems, TxDOT plans to start connecting these islands of information together to improve traffic management between cities.
  • Emergency management: Continued improved coordination between TransGuide and San Antonio's Emergency Operations Center will help facilitate better response and operations during local emergencies, hurricane evacuations and issues related to homeland security.


Closed circuit camera Frontage road DMS

Above: Frontage road DMS

Left: Closed-circuit camera


Freeway DMS

Above: Freeway mainlane DMS displaying travel time information


Lane Control Signals

Above: Lane control signals


Operations Center

Above: Operations Center (inside)


Operations Center

Above: Operations Center (outside)

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This page and all its contents are Copyright 2015 by Brian Purcell

The information provided on this website is provided on an "as-is" basis without warranties of any kind either express or implied.  The author and his agents make no warranties or representations of any kind concerning any information contained in this website.  This website is provided only as general information.  The author expressly disclaims all liability with respect to actions taken or not taken based upon the information contained herein or with respect to any errors or omissions in such information.  All opinions expressed are strictly those of the author.  This site is not affiliated in any way with any official agency.