Antonio Area Freeway System
last updated November 6, 2022
is San Antonio's award-winning, inter-agency Advanced Transportation
System. When it went online in July 1995, it was the most advanced
of its kind in the nation, and it continues to be a leader in
Intelligent Transportation Systems (ITS) technology. The system is now
operational on about 120 miles of freeway in Bexar County and is
currently under construction on about 60 additional miles of freeway.
is a map of
TransGuide's current coverage area and planned future
expansions. "Full coverage" areas shown on the map are the areas with
contiguous camera coverage and more extensive message signs all
connected via fiber optic cable.
"Auxiliary coverage" areas have more widely-spaced cameras
and message signs connected via wireless communications; these can be
thought-of as "TransGuide Lite" areas.
Some of these areas are planned for future upgrades to full coverage.
the late 1980s,
Raymond Stotzer, TxDOT's San Antonio director, instructed the local
district to develop an innovative ITS system that would be a model for
other systems nationally. Ergo, the Texas Traffic Responsive Automated
project was announced in early 1993. The system would eventually be
branded as "TransGuide" and the operations center and initial 26 mile
core section officially went
July 26th, 1995. That original core section consisted of the inner loop
freeways around downtown: I-35 from New Braunfels Ave. to Southcross
Blvd., I-10 West from Hildebrand Ave. to I-35 (with fiber optic cable
then continuing to the TransGuide building at Loop 410), I-10 East and
US 90 from
Zarzamora St. to Roland Ave., and I-37 and US 281 from St. Mary's St.
to Fair Ave.
TransGuide building under
construction in 1994
the past two decades, the full coverage system has been
the past decade or so, "auxiliary coverage" areas (my term; TxDOT is
calling these "gap coverage" areas) have been
added on the periphery of the primary corridors and along the
Interstates into the hinterlands. These areas include
cameras, dynamic message signs, and traffic monitors, but in more
widely-spaced strategic standalone locations to help provide
coverage at reduced cost, sort of a "TransGuide Lite."
from St. Mary's St. to Basse Rd., Loop 410 from Ingram Rd. to I-35
North, I-10 from Fulton Ave. to Camp Bullis Rd., and Loop 1604 from
Babcock Rd. to Lockhill-Selma Rd.
- 2000: I-35 from New
Braunfels Ave. to Starlight Terrace
- 2001: US 90
from Zarzamora St. to Hunt Ln.
- 2002: I-37 from
Fair Ave. to US 181
- 2003: I-35
from Starlight Terrace to Loop 1604, and Loop 1604 from I-10 to Bandera
- 2009: US 281 from
Basse Rd. to Nakoma Dr., and Loop 410 from Ingram Rd. to Culebra Rd.
- 2012: US 281 from
Nakoma Dr. to Winding Way
- 2016: Loop 1604 from
Bandera Rd. to Culebra Rd.
- 2019: Loop 1604 from
Culebra Rd. to US 90, and Loop 410 from Culebra Rd. to SH 151
- 2020: Loop 410 from
SH 151 to US 90
- 2021: I-10 from Loop
1604 to Ralph Fair Rd.
TransGuide was designated as the central TxDOT unit to disseminate
Amber Alerts and other emergency alerts and it continues that role
coordination with TxDOT's Austin district, ITS coverage was extended to
the entire I-35 San Antonio-Austin corridor as the first such intercity
project in the state. TransGuide is responsible for
the section south of the Comal/Hays County line with Austin's
ITS system taking it from there.
2009, TransGuide completed the first major upgrade of their computer
systems and website.
2017, dynamic message signs and cameras were installed at
locations along I-10
Antonio and Ozona.
many years, TransGuide operated a low-power UHF television station on
channel 54 that
broadcast a rotation of video feeds from select traffic cameras for use
by local TV stations, but the signal was also available to
with a UHF antenna. The video was also transmitted on the City of San
Antonio's cable channel during rush hours and emergencies. In 2003,
TransGuide established direct fiber-optic feeds to the local TV
stations along with the capability for them to
select specific camera feeds for their
broadcast. Shortly thereafter, the UHF transmitter was shut down.
completed in 2021 on a major renovation of the TransGuide
center. This project renovated the main operations room and
the obsolete consoles, video walls, and other technology, renovated and
reconfigured offices and support spaces, replaced the building's roof,
the various building utility and mechanical systems. The City of San
Antonio's traffic management center, which has been located in a
separate space in the TransGuide building, then moved into the
main operations room to join the SAPD, VIA, and HERO
Model Deployment Initiative
1996, TransGuide was selected as one of four participants nationally
for the US Department of Transportation's ITS Model Deployment
Initiative (MDI). This program was developed to design, test, and pilot
variety of innovative transportation technologies. In San Antonio,
those included the following:
of these technologies are commonplace today but were quite
innovative for their time as that was before
the ubiquitous Internet
access, GPS, public traffic data, and Wi-Fi that we have today. The
MDI program ended in 1999.
a wireless data system (similar to today's Wi-Fi)
that permitted two-way videoconferencing and data transfer
EMS ambulances and hospitals using the TransGuide infrastructure.
interactive traveler information kiosks at key locations around the
city that provided real-time traffic information as well as
weather reports, bus and airport information, and tourist
of in-vehicle navigation units that displayed real-time
incident information as well as turn-by-turn directions. (A predecessor
to today's GPS apps.)
real-time travel speed data collection using RFID tags distributed to
volunteers and read by antennas placed over traffic lanes at strategic
the city. This data was consolidated into a regional database that
also included data from TransGuide's traffic monitoring, SAPD accident
data, and TxDOT lane closure information. This database was
used by the information kiosks and in-vehicle navigation units.
of the Advanced Warning to Avoid Railroad Delay (AWARD) system that
installed detection equipment at railroad crossings near freeway exits
which allowed drivers to be alerted of delays caused by trains.
Travel time program
1999, TransGuide was among the first ITS systems to display real-time
estimated travel times on dynamic messages signs, which has now become
commonplace nationally. Besides the
explicit information it provides to drivers, one of the major benefits
of showing travel times
confirms to drivers that
the signs and system are operational. Previously, the signs were dark
was an incident, and surveys indicated that many drivers interpreted
the dark signs as the system being offline, which reduced confidence.
After the success of travel time displays in San Antonio and a couple
of other cities, the Federal Highway Administration issued a memo
in 2004 that
recommended travel times be the default message on DMSs.
Initially, travel times were displayed from 6:00am
to 10:00pm. The first generation of travel times just showed the
destination and a travel time range. A recent improvement has added the corresponding distance,
which allows drivers unfamiliar with the route to better correlate the
time to distance and therefore assess downstream conditions.
it was first
developed, the specifications called for TransGuide to be able to
reliably detect incidents within two minutes, quickly verify the
then be able to implement a response scenario that warned drivers
within 15 seconds. To accomplish these goals, TransGuide
uses a variety of technologies and the
system today is composed of the following major components:
traffic operations center (TOC)
closed-circuit, remote-controlled video cameras
detectors at over 200 locations (originally inductive loop detectors in
the pavement, but mostly side-fire radar and Bluetooth readers nowadays)
mainlane dynamic message signs (DMS)
travel time comparison (TTC) signs
divergently-routed fiber-optic rings, wireless transmitters/receivers,
and associated communications
and distributed data systems, specialized software, and related
Traffic Operations Center
The TransGuide Traffic Operations Center (TOC) is
located in the southwest quadrant of the I‑10/Loop 410 interchange on
Northwest Side and houses the system's central computer and
communications equipment and offices for the system's managers and
engineers. The heart of the building is the main operations
which is the "mission control" style room with large video walls
showing various camera and data views and over 30 workstations for the
various operators and dispatchers. In addition to TxDOT's traffic
managers and HERO dispatchers, the San Antonio Police Department and
VIA Metropolitan Transit also have dispatchers in the TOC.
allows seamless coordination between these agencies. The building also
contains rooms for local officials and the media to use during major
2009, the City of San Antonio established their own Transportation and
Infrastructure Management Center in the TransGuide building from which
they monitor traffic on
major arteries and manage the
operation of the city's more than 1,400
traffic signals. Previously, COSA's center was separate from TxDOT's,
but after a renovation in 2021, the city and state centers were
combined in order to improve
coordination and efficiency between them.
around 2010 until 2017, the regional office for the Texas Department of
Motor Vehicles (which was spun-off from TxDOT in 2009) was housed in
the TransGuide building. It has since moved to a location on
it was originally
built, the building was inside of-- and accessible only from-- one of
interchange's cloverleaf ramps. The cloverleaf has since been removed
and today the building is accessible from the eastbound Loop 410 access
by Brian Purcell)
by Brian Purcell)
employs about 250 closed-circuit video cameras along the city's
freeway system so that traffic managers can view and identify
cameras offer full tilt/pan and zoom control. These cameras
used for traffic enforcement and video is not recorded.
traffic camera (left) and contemporary camera (right)
white box with antenna was
part of the Model Deployment Initiative's
EMS wireless communications system.
by Brian Purcell)
originally used in-pavement induction-loop traffic
detectors spaced at half-mile intervals in each lane to monitor traffic
flow in order to detect congestion and associated incidents.
Maintenance of those proved problematic and is no longer used, and over
the past couple of decades, other traffic monitoring technologies have
developed and deployed by TransGuide at various times including
transponder tags, machine vision
acoustic detectors, side-fire radar, and Bluetooth tracking. Due to
funding shortages in the early part of this century, maintenance and
expansion of the traffic monitoring systems took a back seat to
maintenance of cameras and DMSs. Today,
while some side-fire radar and Bluetooth tracking are still in use,
commercial GPS traffic data is the now primary source of traffic data.
Dynamic message signs
Dynamic message signs (DMSs)
text-based messages alerting drivers to incidents or congestion,
providing travel times, or showing periodic safety
reminders, with humorous campaigns often going viral.
addition to the standard mainlane
DMSs, TransGuide also originally deployed frontage road DMSs at
on-ramps, which was unique to San Antonio. However, as with lane
control signals (see below), funding shortages have resulted in the
frontage road DMSs being deactivated and in some cases removed,
and there are currently no
plans to restore them.
Future expansions and upgrades will include full-color, full-matrix
DMSs, which will allow for more flexible messages including
reproductions of official traffic signs and other symbols.
The first such DMS in the state was installed on I-35 near Benton City
Rd. in Von Ormy.
mainlane DMS displaying travel time information
sign was destroyed in a crash in 2017
and was not replaced.
by Brian Purcell)
full-matrix DMS displaying travel time information
color is due to the digital refresh rate of the sign conflicting with that of
by Brian Purcell)
by Brian Purcell)
Travel time comparison signs
In conjunction with the implementation of an Advanced Traveler
Information System in 2021, 17 travel time comparison signs like
the one shown below were installed at various strategic "decision
around the city. These show real-time travel times for two
different routes through or around the city or downtown area so that
decide which route to use. Similar signs are in use elsewhere in the
state, although San Antonio's system is the largest such
deployment to date. These signs differ from the travel
on DMSs in that they are dedicated
this purpose and
a comparison of travel times for two routes instead of single "inline"
times for the route you are on.
time comparison sign
by Brian Purcell)
Lane Control Signals
Lane Control Signals (LCSs) are devices placed over each lane to give
about the downstream status (open/closed) of that lane. LCSs were an
integral part of
TransGuide from its inception. However, due to maintenance
funding shortages in the first couple of decades of this century, the
cost to maintain and operate them was deemed
unsustainable, and eventually spare parts for them were no longer
available. As a result, they were turned-off in late 2009 and have
been removed from some areas. With increased funding now
available, there were discussions for a partial
restoration of the
LCS system, primarily at major interchanges, but it was determined that
the benefits did not warrant the ongoing cost to maintain them. They
will be removed over time as part of other construction projects.
A study in 2007 showed about an 80% compliance rate with LCS and DMS
messages. (Perhaps another corollary of the old 80/20 rule.)
by Brian Purcell)
has had a website since its launch. The original site had a very
rudimentary traffic map and documentation about the TransGuide system.
An upgrade in mid 1998 added an improved map that included incident and
lane closure reports and DMS messages. Camera snapshots and travel
added in 2000. As other ITS systems in Texas came online, TransGuide's
site was merged into a statewide ITS site in 2010. Work is underway to
add streaming video from the cameras.
website traffic map in 1997
TransGuide website in 2000
and future expansions and upgrades
shortages during the first two decades of this century delayed
expansion plans for
system and resulted in a substantial backlog of deferred maintenance.
funding shortage resulted in the decision to permanently disable
the system's lane control signals and frontage road dynamic message
signs in 2009 as discussed above. However, recent increases in funding
have allowed for renewed expansion of the system and a program
to clear the backlog of deferred repairs, upgrades, and expansions. The
2021 winter storm highlighted the importance of ITS and is driving
additional improvements and expansions.
system is currently being expanded into new areas in conjunction with
major freeway construction projects along US 28,
Loop 1604, and I-10 East. Additionally,
work began in mid
on independent expansions of the system on Loop 1604 between
I-10 and I-35, and on US 281 from Nakoma Dr. to Loop 1604. Work also
started in late 2021 to add auxiliary coverage along Wurzbach Parkway,
of the full-coverage system on I-35 South from Southcross to
1604 and on I-37 from US 181 to the San Antonio River. Additionally,
cameras are being installed on I-37 in
Atascosa County and on I-10 between Seguin and Luling, primarily for
monitoring during hurricane evacuations. Future system
expansions are currently planned as part of the SH 151 and US 90 West
expansion projects and the
future phases of the I-10/Loop 410 East interchange project.
expansions and upgrades will include full-color, full-matrix DMSs which
will allow for more flexible messages including reproductions of
official traffic signs and other symbols.
Work is currently underway to make streaming video from the cameras
available on the TransGuide website. It is anticipated that could be
completed in late 2022 or early 2023.
years, several studies have proven the benefits of ITS systems in the
form of reduced secondary collisions, mitigated
congestion (and all that entails) due to expedited incident
clearing and timely 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
in crashes, including a 15% decrease in injury accidents
in response times to incidents
of $1.65 million in time and fuel
fuel savings per major incident
driver compliance to posted instructions from 33% to 80%
of drivers reported DMS signs were "very easy" to understand
of drivers indicated that TransGuide was an efficient way of managing
congestion and notifying motorists
of drivers felt TransGuide was a good use of tax dollars
(Source: Texas Transportation Institute
2011, after a series of wrong-way driver incidents culminating in the
death of a San Antonio Police Department officer, a task force was
established to combat the local wrong-way driver (WWD) problem. The
task force included TxDOT, SAPD, the City of San Antonio Public Works
department, the Bexar County Sherriff's Office, the Federal Highway
Administration, and the Texas Transportation Institute. Their charge
was to identify local WWD hot spots, analyze previous WWD
research, investigate WWD countermeasures implemented elsewhere and
determine those that could be implemented locally, and identify funding
for a WWD countermeasures program.
task force identified several countermeasures to implement including
signage and pavement markings, active/illuminated signage, and
detection technologies. In 2012, TxDOT began work on a pilot project to
install flashing LED wrong way signs on all 29 exit ramps on US 281
north of downtown. That was followed in 2013 by installation of
flashing LED wrong way signs and WWD detection radar as part of a
larger expansion project on I-35 in the Selma area. Later in 2013, WWD
radar was installed on the US 281 locations, and testing of a mainlane
WWD detection and warning system was completed at the Southwest
Institute. That system detects wrong way drivers using radar, then
illuminates multiple wrong way signs to alert the driver. All the ramp
and mainlane WWD radar systems notify operators at TransGuide when a
WWD is detected. TransGuide operators then dispatch police and activate
warning messages on the DMSs along the route to alert drivers.
addition to the above, other countermeasures that have been implemented
include red reflective tape added to the wrong way signposts
increase their visibility, adjustments to the locations of the
reflectors used in off-ramp pavement arrows to reduce loss due to
repeated contact, and
additional, repositioned, and/or larger signage where warranted.
results of the US 281 pilot project were significant with a 29%
reduction in WWD events recorded in the year after the changes were
made. Since then, the system has been improved and expanded to most
freeways in the area. Newer installations include multiple radar units
as well as a camera. When a WWD is detected, the camera takes a
picture, which is then included in the automated notifications to
TransGuide and SAPD. SAPD now also announces WWD incidents over their
radio with an emergency tone.
2011 and 2018, the local WWD system detected and helped stop 67 wrong
way drivers. TxDOT continues to refine, improve, and expand the system.
Spike strips on exit ramps
frequent and seemingly common-sense suggestion made by the
to install spike strips on exit ramps, such as those used in some
parking lots and rental car facilities. However, this idea has been
thoroughly studied and there are several reasons why they would not
work in this application:
strips are designed for very low-speed locations (<10 mph.)
testing with high-speed vehicles as would be found on exit ramps, the
spikes often broke, leaving stubs that damaged the tires of vehicles
traveling the right direction.
strips are hazardous to motorcycles, especially when wet.
and debris build up in the devices over time, which prevents the spikes
from folding down properly and therefore can damage the tires of
vehicles passing over in the right direction or even cause drivers to
lose control. Freezing precipitation can also cause this.
view the strips as a hazard and suddenly reduce their speed, causing
congestion and increasing the chances for rear-end collisions.
vehicles sometimes have to travel on exit ramps in the wrong direction
to more quickly reach accident scenes.
short, although it seems like an obvious solution to the WWD problem,
spike strips have too many "fatal flaws" to be a bona fide option.
Highway Emergency Response Operation (HERO) program,
which patrols the local freeways to assist stalled motorists, clear
debris, and provide traffic control at crash scenes, is operated out of
TransGuide. More details on
the HERO program is on the primer page.
are answers to some frequently-asked questions about TransGuide:
the point of TransGuide? All it ever tells me about is congestion that
I see everyday and already know about.
it's true that many TransGuide messages are about areas of chronic or
recurring congestion that are familiar and well-known to commuters
along those routes. However, these congestion reports are useful to
people who are not familiar with that road (e.g. truckers and tourists
passing through, local residents who don't usually travel that route,
etc.) and are also useful as reminders to regulars to be cautious as
they approach the congestion. Studies have shown that these warnings
improve the traffic flow and safety in the areas where they are used.
TransGuide's original intent, and the area where it really provides
benefits, is reporting on incidents that cause unusual or severe
congestion, and providing those reports in a timely manner to warn
motorists and/or allow them to take alternate routes. Also, TransGuide
can often detect
such incidents before they are even reported by phone and, even when an
incident is first reported by the public, TransGuide is useful in
precise location and extent of it as telephoned reports are
or inaccurate. This helps to ensure that the proper
assistance is dispatched immediately. These factors combine to mean
that TransGuide helps improve response times and results
in incidents being cleared faster.
the point of the travel times on TransGuide signs? I know how long it
takes to get where I'm going.
travel times shown on TransGuide signs are computed every minute based
on real-time traffic conditions. While the times shown during
periods without congestion may seem pointless to those who travel the
road often, they do serve the purpose of reassuring drivers that the
route ahead is clear and that the system is online. Studies
that when DMS signs are blank, many drivers assume the system is not
operating. When the road
is congested and travel times increase correspondingly, motorists
familiar with the typical travel times are able to use the travel times
shown to judge the severity of the
downstream congestion and determine whether or not to use an alternate
- The travel times on TransGuide signs are frequently wrong.
There are a few things to keep in mind regarding the
displayed travel times:
upshot is that travel times are dynamic and the travel time
displays are meant to be general and advisory in nature, not exact
nor guaranteed, and a 2000
survey determined that the vast majority of motorists understand that
travel times are approximate. As a
footnote, test runs after TransGuide's travel time system was
implemented showed 85% of drivers arrived within the displayed travel
time range with the remainder evenly split between early and late
- First, they are based on prevailing traffic speeds,
so if you're
driving significantly above or below those speeds, this will obviously
skew your travel time.
- Secondly, the travel times are a snapshot of the
situation at the
moment they were computed and you see them. Traffic is highly dynamic,
so shortly before you see the sign or soon after you pass it,
downstream conditions could suddenly change and render the last travel
time you saw obsolete.
- Finally, travel times are rounded to the nearest
minute, so for shorter
distances, this could result in a notable (but still trivial)
difference due to that rounding.
still think TransGuide is a waste of money. Why don't they use the
money spent on TransGuide building new highway lanes?
A 1997 study reported that 80% of drivers thought that
was a good use of tax dollars. Much of the funding
for TransGuide comes from funding sources dedicated to
Intelligent Transportation Systems (ITS). As a result, that
money cannot be used for anything other than ITS
projects. If TransGuide didn't get that money, it would simply go to
another city's ITS system. Furthermore, the amount of money spent
on ITS projects is substantially less per mile than roadway expansions,
so using ITS funding for roadway expansion would yield very
few miles of new
Compared to roadway expansions, ITS has been shown to result in a more
substantial and longer-lasting return-on-investment. Regardless, it is
well-understood now that there is a point when you
can no longer just build your way out of congestion. Instead, you have
to better manage what you have, which is the intent of ITS systems, not
to mention the undeniable safety aspects.
sites of interest