The safety of transportation, both surface and air, is
highly dependent on weather. Not only is the safety of transportation impacted
by weather, but so too is the efficiency of operations. Severe weather causes diversions and
delays in air and surface travel.
In all cases, there is a financial impact on commercial
transportation. Intelligent transportation systems (ITS) technology can improve
both the efficiency and safety of surface travel. It also addresses the
intermodal cargo exchange efficiency between surface and air transportation.
Understanding weather conditions and how weather is predicted to impact surface
travel is an important element of traveler information of interest to the
private and commercial traveler and the commercial fleet dispatcher.
Thus, one of the most important sensors associated with ITS
involves roadway weather conditions sensing and reporting.
This article discusses ITS technology as it relates to
weather and as deployed in intelligent transportation subsystems referred to as
roadway weather information subsystems (RWIS).
RWIS
Remote sensing of weather is not a novel idea; remote
weather sensors have been available since the 1930s. The sensors were
originally deployed for National Weather Service forecasting and support to the
U.S. Army Corps of Engineers for water resource and flood control management.
In the 1960s, communications and sensor technology allowed
weather sensors deployment in support of roadway weather forecasting. The
safety of transportation, both surface and air, is highly dependent on weather.
Not only is the safety of transportation impacted by weather, but so too is the
efficiency of operations. Severe
weather causes diversions and delays in air and surface travel.
In all cases, there is a financial impact on commercial
transportation. Intelligent transportation systems (ITS) technology can improve
both the efficiency and safety of surface travel. It also addresses the
intermodal cargo exchange efficiency between surface and air transportation.
Understanding weather conditions and how weather is predicted to impact surface
travel is an important element of traveler information of interest to the
private and commercial traveler and the commercial fleet dispatcher.
Thus, one of the most important sensors associated with ITS
involves roadway weather conditions sensing and reporting.
RWIS ranks high with travelers in surveys of perceived
benefits of ITS technology deployment. Post RWIS deployment surveys of users
indicate that 94% feel that RWIS is beneficial. Perhaps RWIS and motorist
assistance patrols would be closely ranked at the top of ITS deployments
perceived by travelers as the most beneficial in supporting travel security and
safety.
Even more important is the fact that RWIS deployments by
jurisdictions are providing a much denser sampling of roadway weather
conditions making possible more accurate assessment of the weather's impact on CVO. Making
RWIS data available to National Weather Service (NWS) Field Weather Forecasting
Centers provides many additional point sources of information to assist NWS in
making a more accurate, regional forecast.
Making traveler info more accessible
In the early 1990s, emphasis on traveler information and distribution
was placed on the public traveler. With NAFTA becoming a reality, in the
mid-1990s the FHWA and state DOTs started equally emphasizing efficiency and
safety of commercial vehicle operations. The Commercial Vehicle Integrated
Services Network (CVISN) was established to integrate CVO functions on a state
and national basis. The concept of deploying commercial traveler information
service focusing on the needs of the commercial vehicle dispatcher and driver
emerged in the late 1990s and continues today.
State DOTs are starting with the deployment of kiosk
terminals at rest stops, state border welcoming centers and at truck stops to
make commercial travel information more accessible. Most commercial drivers
have either cellular or satellite digital links to theirhe safety of
transportation, both surface and air, is highly dependent on weather. Not only
is the safety of transportation impacted by weather, but so too is the
efficiency of operations. Severe
weather causes diversions and delays in air and surface travel.
In the 1960s, communications and sensor technology allowed
weather sensors deployment in support of roadway weather forecasting. Companies
emerged that provided special weather forecasting for commercial vehicle
operations (CVO). With minicomputers providing affordable routing and trip
planning capabilities, the surface transportation oriented weather forecasts
became a critical element of commercial vehicle dispatching operations. CVO
delays due to snow, ice and significant head winds were considered versus the
cost associated with less direct routing in execution of the automated
commercial vehicle dispatching function.
Technology continued to improve with the emergence of
microprocessors in the late 1970s. Today, microprocessor-managed roadway
weather information systems are deployed in most states which experience severe
weather and/or flooding. RWIS is being deployed by the DOT and traffic
management of state, county and large city governments. ITS traffic management
centers—and in some cases, the departments of public safety emergency
management centers—collect RWIS information, which is utilized to prepare
traveler information corridor conditions reports. Traveler information is made
available to the public via Internet web pages, 511 access, public broadcast
media and cellular telephone traveler services.
The traffic management centers also use directly linked
dynamic message signs (DMS) and highway advisory radio (HAR) devices to
communicate with en-route travelers. Some RWIS include automatic messaging to
departments of public safety and roadway maintenance personnel via pagers and
digital cellular interfaces, thus alerting them of weather transition to
hazardous road conditions.
Benefits of ITS
RWIS ranks high with travelers in surveys of perceived
benefits of ITS technology deployment. Post RWIS deployment surveys of users
indicate that 94% feel that RWIS is beneficial. Perhaps RWIS and motorist
assistance patrols would be closely ranked at the top of ITS deployments
perceived by travelers as the most beneficial in supporting travel security and
safety.
Even more important is the fact that RWIS deployments by
jurisdictions are providing a much denser sampling of roadway weather
conditions making possible more accurate assessment of the weather's impact on CVO. Making
RWIS data available to National Weather Service (NWS) Field Weather Forecasting
Centers provides many additional point sources of information to assist NWS in
making a more accurate, regional forecast.
Making traveler info more accessible
In the early 1990s, emphasis on traveler information and
distribution was placed on the public traveler. With NAFTA becoming a reality,
in the mid-1990s the FHWA and state DOTs started equally emphasizing efficiency
and safety of commercial vehicle operations. The Commercial Vehicle Integrated
Services Network (CVISN) was established to integrate CVO functions on a state
and national basis. The concept of deploying commercial traveler information
service focusing on the needs of the commercial vehicle dispatcher and driver
emerged in the late 1990s and continues today.
State DOTs are starting with the deployment of kiosk
terminals at rest stops, state border welcoming centers and at truck stops to
make commercial travel information more accessible. Most commercial drivers
have either cellular or satellite digital links to their associated dispatching
centers supporting automatic vehicle location and computer-aided dispatching.
As a result, by linking dispatching centers to roadway weather via CVISN, the
information can be responsively communicated to the commercial driver. As
digital short range communications deployments utilizing the new ITS IEEE
802.11a standard emerge at automated CVO clearance stations and commercial
vehicles are fitted with integrated driver information systems, this link may
be an appropriate warning to commercial drivers of hazardous roadway weather.
Specific CVO requirement
Roadway weather sensor systems technology has also evolved
to consider specific commercial vehicle operational safety requirements.
The Oregon DOT was one of the first to deploy weather
sensors integrated with weigh-in-motion and speed detection sensors to warn a
commercial vehicle of dangerous conditions. The remote, roadside processor considered
grade, vehicle speed, vehicle weight, as well as road conditions based on
weather sensor inputs. A dynamic message sign is utilized to warn the driver of
the commercial vehicle to reduce speed based on current conditions.
Ice, snow and wet roads obviously negatively impact both
private and commercial travel thus, the drivers' knowledge of their presence on
the road surface is very important to safety. As most drivers know, bridges
develop icy conditions prior to roads because bridges do not have a latent heat
source comparable to that of the road's subsurface.
Therefore, understanding weather conditions, which will
result in the formation of ice on bridges, is an important function of RWIS.
Determining the dew point temperature and road surface temperature assist in
determining probable icing conditions on bridges. High head winds can increase
the fuel consumption for commercial vehicles, even if they include wind
diverters. High gust side winds on the large area surfaces of commercial
vehicle trailers can cause safety hazards, especially if the vehicle is
transitioning a curve.
Thus the commercial driver and his dispatcher are interested
in wind speed and direction at ground level and whether the wind is constant or
gusty and maximum velocity of gusts.
This is basic information available from RWIS.
Also of interest to both private and commercial drivers is
the status of sanding/deicing and clearance of the snow from corridors, which
have experienced freezing precipitation.
The number of lanes prepared for safer travel after freezing
precipitation is also of interest. This information must come from the public
works organization responsible for corridor sanding/salting and snow removal.
Intelligent transportation systems are now being deployed
with automatic vehicle location and mobile data terminals on vehicles that
support snow clearance and road treatment for deicing. These vehicles are
managed by a dispatching center or a position within the jurisdictional traffic
management center. Corridor snow clearance and deicing status is available for
integration with other information related to safe travel, congestion
management and incident management for distribution to travelers.
Predictive weather information
What all travelers desire is accurate predictive
information. They want to be aware of road conditions when they arrive and they
want local travel information to validate the predictions. The forecast of
roadway conditions as impacted by weather is critical to trip dispatching from
a safety and economics standpoint for commercial transportation. Significant
work has been accomplished by Georgia Technical University's Research Center
related to predictive traveler information.
Algorithms utilizing information on historical
time-of-day/day-of-week corridor congestion and travel time statistics as well
as statistics on special events of the same or similar types are utilized to
develop predictions of travel time. Also to be accurate and reliable,
predictive travel information must consider weather forecasts as related to
surface travel.
Weather forecasting is much more advanced than predictive
travel information. Meridian
Environmental Inc. is providing roadway weather forecasting services for
several states including North and South Dakota and Arizona. However, their
traveler information services are only weather related and not all-inclusive.
Most travelers desire "one stop" traveler information, which was the
emphasis of the 511 initiative by FHWA.
Roadway weather forecasting centers are now emerging,
especially in the northern states, which have severe winter weather. These
centers integrate both NWS information with RWIS reported information. Roadway
weather forecasts are made and generally published on a webpage. Standards
initiatives are under way to develop standards of presentation for driver
weather information. Detection of parcipitation type and rate is considered in
the forecast as well as roadway surface and subsurface temperature in relation
to the atmospheric temperature above the road. A prediction of accumulation of
freezing precipitation over time is included in weather modeling software. The
thermal inertia of the road subsurface as well as the road surface (based on
the type of materials utilized to construct the road) and current temperature
are major considerations related to the forecast.
Similarly, density of traffic can add thermal energy to the
surface.
Obviously, there may be a period where the thermal inertia of
the road and the added heat from vehicles cause freezing precipitation to melt.
The precipitation rate and type measured by RWIS also provides information on
driver visibility impact and probable slow down of traffic. Many of the RWIS
deployed by state DOTs also include visibility sensors that can provide
quantitative measurements of visibility. These are very beneficial in areas
susceptible to heavy precipitation and fog.
The NWS has provided weather forecasts for many years. With
the advent of multi-spectral weather satellites; the deployment of a much
higher density of remote, robotic weather sensors; and the improvements in
weather modeling technology, the accuracy of weather forecasting has greatly
improved since the 1970s.
For roadway weather forecasting to be reasonably accurate,
RWIS information must be integrated with NWS data. Equally important in
reliable roadway weather forecasting is consideration of terrain and
understanding of usual weather patterns. The forecast roadway weather is not only
valuable to drivers but also to the freezing precipitation clearance crew and
to the emergency service resources that respond to incidents on the corridors.
Human factors studies indicate that an 80% accuracy of
information is necessary for drivers to conform to advisory messaging. If
drivers find traveler information provided to them to be unreliable (greater
than 20% error rate), they may ignore the information or go to another source
of traveler information. This provides a challenge for the development of
predictive traveler information, which is based on probability theory and a
reason that state DOTs must pay close attention to the quality of their roadway
weather forecast that they disseminate to drivers.
Freezing precipitation clearance
Technology is available today that supports the removal of
freezing precipitation for corridors by automatic release of deicing agents or
by raising the temperature of the surface of the corridor.
Early deployment tests have shown that the technology works.
Embedded RWIS sensors in the road surface verify the presence of deicing
chemicals and temperature of the road (above 32ºF). Deployment focus is
now on bridges, which ice more rapidly than non-bridge road surfaces. Advocates
indicate that cost savings of automated deicing versus manual deicing results
in a benefits/cost ratio justifying deployment. Furthermore, studies indicate
that deicing can reduce accident rates by more than 80%, which supports the
deployment benefits derived.
RWIS sensor technology
A typical RWIS deployment usually consists of a 10-meter
tower. There are a number of types of sensor technologies and the type of
technology selected impacts accuracy. Intrusive road sensors provide more
information and more accuracy than non-intrusive sensors, however, reliability
and required maintenance is a major issue. Detection of the presence of deicing
fluids requires intrusive sensors, however research is under way to utilize
multi-spectral sensors to determine chemical presence and type. This technology
is commonly utilized for remote sensing of water pollution and can discriminate
even different types of petroleum contaminants on the surface of water.
Flood sensors may be optionally utilized if the roadway is
subject to flooding. In areas where severe storms are probable, a lightning
detection sensor may also be deployed. Some RWIS are deployed with
day/night-light level sensors that complement visibility sensors. For critical
measurements, redundant sensors may be utilized and some may utilize "voting"
between the three where any sensor that does not provide a value comparable
with the other two is "voted out" and the remaining two are averaged
to provide the reported measurement value.
The RWIS electronics manage sensor sampling rate and reports
calculated parameters such as maximum wind gust over a sampling period and wind
direction and velocity over an averaging period. It also calculates dew point
and can report measured parameters in various units as required by the DOT
deploying the sensors. Because the majority of the travelers in the U.S. prefer
non-metric, these are widely used (i.e., temperature in °F; wind velocity
in miles per hour; barometric pressure in inches of mercury; etc.) RWIS is
usually deployed with an uninterruptible power system (UPS). Some
configurations are available that will support "plug-and-play"
installation where power is via a UPS with solar recharging.
RWIS is usually deployed using a 10-meter tower, which
provides adequate height for wind velocity and direction measurements and
visibility measurements. It also provides a platform for mounting a CCTV
camera, if there is not a utility pole available. RWIS electronics should
comply with NEMA TS-2 controller environmental standards.
RWIS communications
A variety of communications techniques are utilized.
Cellular and dial-up phone lines are common. Use of cellular "smart
emergency call boxes" with RWIS integration was pioneered by Caltrans in
the early 1990s. Wireless digital links are also common and operate effectively
if properly designed. Where freeways have optical communications links,
interconnect with the ITS communications network is utilized.
Internet links are also available. Usually, RWIS
automatically report preprogrammed alarm condition to a central data collection
system and are periodically polled to validate operation and to obtain routine
weather statistics. Type of communications utilized depends on location,
terrain, available communications support infrastructure and budget for RWIS
deployment.
Benefits of RWIS
A number of post-deployment analyses have been conducted.
NCHRP Project 20-7 Final Report by S. E. Boselly identifies benefit/cost ratios
of up to five for RWIS with automated deicing.
Robert Stowe's report, A Benefit/Cost Analysis of ITS
Applications for Winter Maintenance, presented at the January 2001
Transportation Research Board 80th Annual Meeting, contributes a 2.36
benefit/cost attributed to RWIS related deployments by WSDOT.
The true benefits of RWIS are directly related to the
severity of weather in the region, miles and geometry of rural and urban
corridors subjected to severe weather, traffic volume on corridors and percent
utilization by commercial vehicles, effectiveness of roadway weather
forecasting and whether automated deicing equipment was incorporated with RWIS.
Most of the RWIS studies indicate a reduction of accidents and loss of property
and lives of from 25 to 50%.
The Salt Institute, in an article titled Highway Deicing and
Anti-icing for Safety and Mobility, presents a figure of 88.3% reduction in
loss of life and property by roadway maintenance being proactive to winter
weather. If a 50 to 80% reduction in loss of life and property is supportable
by RWIS, then benefits/cost should be much greater than 3 to 5.
In an article by S. Borenstein titled, Elderly Less Valuable
in Cost/Benefits Analysis, the U.S. Office of Management and Budget is quoted
as using $3.7 million for the value of a person's life under the age of 70.
Thus, assuming that two lives would be saved per year would equate to a $74
million benefit over 10 years. The cost of deploying a single RWIS is
approximately $100,000 per site.
Typically, states deploy 40 to 80 RWIS stations. Assuming
$200,000 annual maintenance cost and $500,000 forecasting cost per year plus deployment
cost of $8 million, equates to $15 million in cost of RWIS over 10 years.
(Deployment cost alone will be around $4 to $8 million.) Benefits also include
cost savings of deicing chemicals, which WSDOT projected to be approximately
$2.5 million over 10 years. There is also the cost savings of highway
maintenance fuel and improved crew efficiency. Also included is the reduction
in travel delays through better trip planning that could easily equate to
several million dollars per year ($20 million in 10 years). In 10 years it is
reasonable to assume a $100 million benefit with a $15 million cost (a 7:1
benefit/cost ratio).
RWIS is a key ITS sensor. RWIS is valuable for states that
do not experience ice and snow, but experience heavy rain and fog. RWIS is
extremely valuable in states that experience ice and snow.
Today, most of the states have deployed some form of RWIS.
RWIS technology will continue to evolve as well as Roadway Weather Forecasting
Centers becoming an integral part of ITS Regional Traveler Information Centers
or Regional Construction/Maintenance Management Centers. Forecasting centers
with an understanding of the terrain and road network are important to accurate
forecasting as demanded by travelers. RWIS is important to private and commercial
travelers and equally important to emergency management and roadway
maintenance.
Additionally, RWIS information is very valuable to NWS, the
U.S. Army Corps of Engineers and U.S. Forest Service helping to enhance their
weather database for managing water and forest resources and public safety.
RWIS will also play a major role in homeland security as
related to supporting weather inputs for modeling of the spread of chemical and
biological agents, if deployed by terrorists. It is also possible to integrate
chemical and biological agent sensors with RWIS, especially if RWIS is deployed
in or around a metropolitan area.
The benefits/cost of deploying RWIS is significant.
Technology will evolve to make RWIS more reliable and more accessible to users.
Deploying an integrated RWIS as shown is very important to maintaining
efficiency and safety of travel within the state that experiences severe
weather. TME
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