Civilian Benefits of Discontinuing Selective Availability
May 1, 2000
Discontinuing the use of Selective Availability (SA) will improve the predicted
accuracy of GPS for civilian users from within 100 meters (about 300 feet) to within
20 meters (about 60 feet). In many cases, real-world users will find the accuracy
to be even better. This performance boost will enable GPS to be applied in its most
basic form to a variety of civilian activities -- land, sea, air, and space -- where
it could not previously.
The increased performance of GPS, which is broadcast free of charge to the entire
world, is expected to accelerate its acceptance and use by businesses, governments,
and private individuals around the globe. This should lead to increases in productivity,
efficiency, safety, scientific knowledge, and quality of life. It should also fuel
the continued growth of the global GPS market, currently estimated at over $8 billion,
as well as the market for geographic information services in general.
Listed below are several examples of the civilian benefits derived from discontinued
use of SA.
- Car Navigation: Previously, a basic GPS-based car navigation system could
drift off course by one or two blocks, leading to erroneous guidance and directions.
In areas where multiple highways run in parallel, SA made it difficult to determine
which one the car was on. Terminating SA will eliminate such problems, leading
to greater consumer confidence in the technology and higher adoption rates.
It will also simplify the design of many systems (e.g. eliminate certain map
matching software), thereby lowering their retail cost.
- Fleet Management: Companies managing fleets of vehicles such as taxicabs,
buses, commercial trucks, and rental cars will enjoy increases in efficiency
as their ability to track and route individual vehicles improves. This will
be especially important in crowded parking lots and railroad yards, where SA
previously made it impossible to identify specific vehicles, tractor trailers,
or boxcars using GPS alone.
- Delivery Services: Message couriers and package and cargo transportation
companies will also benefit from better real-time tracking and management of
assets. Automakers and other manufacturers operating under the "just-in-time"
assembly philosophy will get a better handle on when component shipments will
arrive and where they are within the factory grounds.
- Aviation: The removal of SA will improve the accuracy of unaugmented GPS
receivers. This increased accuracy improves safety by aligning pilots more closely
with the runway during instrument approaches, and improving the accuracy of
terrain awareness, warning systems and moving map displays that provide situational
awareness to the pilot.
- Fisheries Enforcement: The U.S. commercial fishing fleet currently relies
on the Loran-C Navigation system because of its excellent repeatable accuracy
and because it provides greater coverage than the maritime DGPS network. The
improved basic GPS will provide commercial fishermen with an even better repeatable
accuracy over an unlimited area. In addition, both fisherman and law enforcement
agencies will share a common, higher accuracy navigation system, possibly leading
to reduced violations of fisheries boundaries, exclusive economic zone issues,
- Highway/Waterway Maintenance: For the first time, many state and federal
transportation authorities will be able to use basic, unaugmented GPS receivers
for highway and waterway maintenance and management, lowering the cost and effort
involved with these activities.
- Nationwide DGPS: The Department of Transportation is currently fielding
the Nationwide Differential GPS (NDGPS) network to improve the accuracy and
integrity of GPS for surface and maritime users across the United States to
the 1-3 meter range. In addition, 34 countries around the world have already
installed DGPS radiobeacon networks, and more are considering the adoption of
this navigation standard. The improvement of the basic GPS signal through elimination
of SA may allow the NDGPS radio beacons to transmit fewer error corrections
and more value-added navigation messages, improving highway, railroad, and waterway
safety. The range of individual NDGPS stations is also expected to increase,
benefiting mariners farther off shore and opening the possibility of reducing
the overall number of stations to be fielded. This flexibility allows for a
more cost effective network for the government and the nation. In addition,
the complexity of all DGPS systems will be reduced, lowering costs for those
who will be using this technology.
- Firefighter/Police/Ambulance Dispatch: Reducing the positioning error from
100 meters to 20 meters or better will make an enormous difference in pinpointing
the locations of fires, crime scenes, and accident victims and routing emergency
crews to the scene. In such life-threatening situations, every second saved
- E-911: The FCC will soon require that all new cellular phones be equipped
with location determination technology to facilitate "911" call responses. Removing
SA would boost the accuracy of GPS to such a degree that it could become the
method of choice for implementing the E-911 requirement. A GPS based solution
might be simpler and more economical than alternative techniques such as radio
tower triangulation, leading to lower consumer costs.
- Search and Rescue: With SA turned off, GPS will become a more powerful and
compelling tool in helping rescue teams search for individuals lost at sea,
on mountains or ski slopes, in deserts, and in wilderness environments.
- Roadside Assistance: Disabled cars equipped with GPS systems such as OnStar
will be able to more accurately transmit their location, speeding response times
for tow trucks and other services. With SA zeroed, the car's GPS signal will
be able to identify which side of the road the car is on -- an extremely important
distinction if the local road, or interstate freeway, is divided by a concrete
- Emergency Preparedness: Relief agencies such as the Federal Emergency Management
Agency (FEMA) will be able to use basic, standalone GPS receivers to map out
geographical features such as flood plain boundaries, levees, and drainage ditches
-- a task that previously required expensive and labor intensive GPS augmentation
- Mineral and Resource Exploration: In many cases, removal of SA will eliminate
the need for costly differential correction equipment and services as companies
explore remote, uncharted geographic regions for minerals, oil, coal, and other
- Resource Management: Agencies such as the Bureau of Land Management and
the Forest Service will be able to apply basic GPS to the management of wetlands,
forests, and other natural resources without the use of costly augmentation
systems or, in some cases, tightly controlled, highly burdensome military receivers.
This should reduce government costs and increase productivity. Similarly, paper
and lumber companies may be able to identify and manage individual trees to
using basic GPS.
- Wildlife Tracking: Scientists and other individuals seeking to observe and/or
tag animals in the wild will have a more powerful positioning and tracking tool
at their disposal. This includes zoologists, ecologists, marine biologists,
and communities seeking to safeguard themselves from animal threats (e.g., wolves).
- Hiking, Camping, and Hunting: GPS is already popular among outdoorsmen,
but the degraded accuracy has not been good enough to ensure that they will
not get lost or lose items (such as game) left behind for later recovery. With
20 meter accuracy or better, hikers, campers, and hunters will be able to navigate
their way through unmarked wilderness terrain with greater confidence and safety.
And for the first time, users will find that the accuracy of GPS actually exceeds
that of the commonly used U.S. Geological Survey (USGS) topographical quad maps.
- Boating and Fishing: Recreational boaters without DGPS equipment will enjoy
safer, more accurate navigation around sandbars, rocks, and other obstacles.
Fishermen will be able to more precisely locate their favorite spot on a lake
or river. Lobster fishermen will be able to find and recover their traps more
quickly and efficiently.
- Satellite Tracking: NASA satellites using GPS receivers will be able to
determine their orbit positions more accurately. For example, satellites using
GPS Standard Positioning Service signals, orbiting at around 700 kilometer altitude,
will be able to go from the present 100 meter level of accuracy for orbit position
determination to about 10 meter accuracy in near real time. This will enable
improvements in science observations and satellite operations.
- Satellite Data Processing: The processing of science data using differential
GPS techniques, such as is done in the rapid production of El Niņo weather maps,
will be accomplished more economically. The increased accuracy of the signals
received at NASA's Global GPS Network will allow reduction in the rate of data
collection, thus reducing communication costs for data used to generate science
results from satellites such as TOPEX/Poseidon.
- Future Space Station Operations: Among the many benefits that may be realized
by space users of GPS in the future will be simplification of systems supporting
critical rendezvous operations and navigation of "Free Fliers" near the International
Space Station. The elimination of SA may enable the performance of early satellite
rendezvous operations to be greatly simplified and may significantly enhance
the performance of relative GPS during close in maneuvering operations.
- Increased Adoption of GPS Time: In addition to position information, the
accuracy of the time data broadcast by GPS will improve to within 40 billionths
of a second. This improved level of precision may encourage continued adoption
of GPS as a preferred means of acquiring Universal Coordinated Time (UTC) and
for synchronizing everything from electrical power grids and cellular phone
towers to telecommunications networks and the Internet. For example, with higher
precision timing, a company can stream more data through a fiber optic cable
by tightening the space between data packets. Using GPS to accomplish this is
far less costly than maintaining private atomic clock equipment.
Need for Higher Performance
Even with SA turned off, GPS alone will not meet all users needs. For users with
higher accuracy, availability, and integrity requirements -- such as commercial
airlines, ships navigating within harbors, railroads performing precise train control,
precision farmers and miners, and surveyors -- GPS will still need to be augmented
locally with high-fidelity error correction systems based on differential GPS (DGPS)
technology. The U.S. is also adding two new civilian signals to future GPS satellites
to further improve accuracy and reliability on a global basis. But for the many
other users listed above, the elimination of SA will enable the most inexpensive,
standalone GPS receivers to meet their needs.
Additional information about GPS and the Interagency GPS Executive Board is available
online at http://www.igeb.gov