Antonio Area Freeway System
last updated July 17, 2021
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 115 miles of freeway in Bexar County and is
currently under construction on about 40 additional miles of freeway.
is a map of
TransGuide's current coverage area and planned future
expansions. Areas shown on the map are the fully-instrumented areas,
there are also some standalone TransGuide elements such as cameras
and message signs outside the fully-instrumented areas.
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 ring of
freeways around downtown: I-35 from New Braunfels Ave. to Southcross
Blvd., I-10 West from Hildebrand Ave. to I-35, 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 system has been gradually expanded:
the past few years, various elements of TransGuide, such as
cameras, dynamic message signs, and traffic monitors,
have been installed at several strategic standalone locations
outside of the
fully-instrumented sections to help provide additional regional
- Early 1999: US 281
from St. Mary's St. to Basse Rd., Loop 410 from I-10 to Ingram Rd., and
I-10 from Fulton Ave. to Wurzbach Rd.
- August 1999: I-10
from Wurzbach Rd. to Camp Bullis Blvd., Loop 1604 from Babcock Rd. to
Lockhill-Selma Rd., and Loop 410 North from I-10 to I-35
- 2000: I-35 from New
Braunfels Ave. to Starlight Terrace
- June 2001: US 90
from Zarzamora St. to Hunt Ln.
- May 2002: I-37 from
Fair Ave. to US 181
- April 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 Dr.
- 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
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. These travel times, along with traffic camera
snapshots, were added to TransGuide's website in 2000. Besides
information to drivers, showing travel times confirms to drivers that
the system is operational. Previously, the signs were dark unless there
was an incident, and surveys indicated that many drivers interpreted
the dark signs as the system being offline, which reduced confidence.
TransGuide was designated as the central TxDOT unit to disseminate
Amber Alerts and other emergency alerts.
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.
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 that
broadcast a rotation of feeds from select traffic cameras. In 2003,
TransGuide established direct fiber-optic feeds to local television
stations along with the capability to select specific camera feeds for
broadcast. Shortly thereafter, the UHF transmitter was shut down.
began was 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 roof, and
the various building utility and mechanical systems. The City of San
Antonio's traffic management center will soon move into the
main operations room to join the SAPD and VIA dispatchers and TxDOT
traffic managers there.
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
considered innovative for their time as that was before Internet
access, GPS, and Wi-Fi were as prolific and ubiquitous as they are now.
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
motorists 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.
The MDI program ended in 1999.
Current and future expansions
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. However, recent increases in funding have allowed for
renewed expansion of the system and a program
to clear the backlog of deferred repairs
are also hoping to eventually revive lane control signals at
system is currently being expanded into new areas in conjunction with
major freeway construction projects along US 281 north of
Loop 1604, I-10 from Camp Bullis Rd. to Leon Springs, and I-10 East
from Loop 410 to Pfeil Rd. Additionally, work began in mid
on standalone expansions of the system on Loop 1604 between
I-10 and I-35 and US 281 from Nakoma Dr. to Loop 1604. Future expansion
of the system is planned on I-35 South from Southcross to Loop 1604, in
conjunction with expansion projects on SH
151 and on I-10 East from Pfeil Rd. to the Guadalupe county line, and
as part the reconstruction of the I-10/Loop 410 East
interchange. Additionally, cameras are being installed on I-37 in
Atascosa County and on I-10 between Seguin and Luling.
project to construct an Advanced Traveler Information System (ATIS) began
early 2019 and is nearing completion. This project includes
the installation of 17
travel time comparison signs at major route decision points throughout
the area, 40 additional
Bluetooth readers to improve travel time calculations, and new
message signs and
the southern fringes of the city. The travel time comparison signs show
motorists the fastest route to
take through or
around the city based on real-time 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 (mostly side-fire radar and Bluetooth readers) at over 200
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 is the heart of the system. In addition to TxDOT,
the San Antonio Police Department
and VIA Metropolitan Transit have dispatchers co-located in the TOC.
coordination with these agencies during major traffic incidents.
2009, the City of San Antonio established their own traffic 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. Currently, COSA's center is separate from TxDOT's,
but work was recently completed that will allow the two center
to combine in order to improve
coordination and efficiency between them.
by Brian Purcell)
by Brian Purcell)
employs about 200 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.
closed-circuit traffic camera
The 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. Over
the past couple of decades, other traffic monitoring technologies have
developed and deployed including transponder tags, video/machine vision
acoustic detectors, side-fire radar, and Bluetooth tracking, all of
which have been implemented at various times by TransGuide. Today,
side-fire radar and Bluetooth tracking are the main technologies
employed. Due to the aforementioned
funding shortages, maintenance and expansion of the traffic monitoring
systems has taken a back seat to maintenance of cameras and DMSs, so
most corridors no longer have
comprehensive passive traffic monitoring. With recently increased
restoration of this capability is a priority, and TransGuide now also
uses traffic data from commercial sources.
Dynamic message signs
Dynamic message signs (DMSs)
text-based messages alerting drivers to incidents or congestion ahead
or on an intersecting freeway. In 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.
mainlane DMS displaying travel time information
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 times shown
on DMSs (like the one shown above) in that they are dedicated to
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) placed over each lane give motorists
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, the cost to maintain and operate them was deemed
unsustainable and they were switched-off in late 2009 and have since
been removed from some areas. However,
with recent funding increases, there are discussions for a partial
restoration of the
LCS system, primarily at major interchanges.
by Brian Purcell)
LCSs can display one of the following
symbols to guide motorists into the appropriate lanes:
law requires motorists to obey LCS signals. A survey in 2007 showed
about an 80% compliance rate with LCS and DMS messages. (Perhaps a
different corollary of the old 80/20 rule.)
years, several studies have proven the benefits of ITS systems in the
form of reduced secondary collisions, mitigated
congestion (and all that 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
been a leading innovator in the ITS field since its inception. In
the future, TransGuide will continue to develop and implement new
technologies to improve traffic management. Besides the continued
physical expansion of the system as discussed above,
other plans for TransGuide include the following:
Traveler Information System: A
project to construct an Advanced Traveler Information System (ATIS)
began in March 2019 and is now substantially complete. This project
included the installation of 17 travel
time comparison (TTC) signs at major decision points citywide, 40
additional Bluetooth sensors to improve travel time calculations, and
new DMSs and cameras on the southern and eastern approaches to the
city. The purpose of this system is to give motorists information
on the best routes to take through or around the city.
With ITS systems now in all of Texas' major metro
areas, TxDOT has connected these islands of information
together to provide seemless statewide coverage and is in the process
of expanding coverage to major routes between the metro areas.
Expansion to the San
Antonio/Austin corridor in 2008 was the first such project.
of City of San Antonio traffic management center: Moving
the COSA TMC to the main TransGuide operations floor will result
in improved coordination between TransGuide and the City of
Antonio's traffic operations center and facilitate better
response during incidents and emergencies. This project is
- Restoration of lane control
The LCS system was switched-off in late 2009 due to a lack of
maintenance funding. Over the next few years, some LCS gantries
will resume operation, mainly in the vicinity of major interchanges.
- Restoration of traffic sensors:
Like the LCS system, funding shortages have resulted in the loss of
numerous traffic sensor locations due to deferred maintenance. This has
reduced the ability
of TransGuide to monitor traffic flow along many corridors. With recent
increases in funding, restoration of this equipment is a high
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, 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
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.
- Drivers may
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 locations.
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.
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 allow
motorists to take alternate routes. Also, TransGuide can often detect
such incidents before they are even reported by phone and, even when an
accident is first reported by the public, TransGuide is useful in
precise location and extent of the incident 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
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 safety aspects.
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