4.0 Data Sources for Weather and Traffic Analysis
Using proper data sources can generate accurate and reliable results from a traffic analysis. For traffic analyses that focus on the impact of inclement weather conditions on the transportation system, weather and traffic data sources are required to complete the analysis. This section discusses the weather data sources, traffic data sources and Intelligent Transportation Systems (ITS) data sources available for weather-related traffic analysis.
4.1. Weather Data Sources
When conducting studies on the impact of inclement weather on traffic operations, collecting the proper weather-related data is essential. The most common weather-related data that is used in the evaluation of weather impacts on transportation are precipitation type, precipitation intensity, and visibility level. Weather Adjustment Factors (WAFs) are a function of these weather-related parameters. Agencies can use these WAFs within the weather module of DYNASMART-P and within microscopic modeling tools to assess the weather impacts on transportation. The advancement in technology has allowed weather-related data, necessary for impact assessment, to be available on the Web. This section presents examples of existing weather data sources that can be accessed online.
Clarus is an excellent source for accessing weather-related data for use by the transportation system. Clarus is designed to display current and forecasted weather-related data for a particular region Sensors that are used to collect traffic data vary among the different State DOTs. Therefore, the quality and format of the traffic data varies as well. Fortunately, Clarus provides users with data that share a common format. Convenience is a key characteristic of Clarus. Current users can access weather-related data for 38 States in the United States and 3 provinces in Canada, as shown in Figure 4-1.
Figure 4-1 Snapshot of Clarus Portal
Users can obtain detailed weather data such as air temperature, average wind direction, average wind speed, precipitation type, and precipitation rate from Clarus in either metric or English units. Incorporating the weather-related data available at Clarus can make data collection less time consuming and less costly as well.
In addition to Clarus, weather data is available online at the National Climatic Data Center (NCDC) website. This organization offers climate and weather information including temperature, precipitation, extreme weather events (e.g., hurricanes and tornados), and snow extremes. A snapshot of NCDC's webpage is shown in Figure 4-2.
Figure 4-2. National Climatic Data Center Website
From the NCDC website, users can access heavy rainfall frequencies provided by the National Oceanic and Atmospheric Administration's National Weather Service Hydrometeorological Design Studies Center. This weather data source allows user to be specific in their search for heavy rainfall frequency by providing options for data description (e.g., data type, units, and time series type) and location within a State. Weather data from NCDC can be obtained from the following link.
Developed by the Department of Atmospheric, Oceanic and Space Sciences at the University of Michigan, UM Weather, shown in Figure 4-3, provides the public with up-to-date weather data on the Web.
Figure 4-3. UM Weather Homepage
Users of UM Weather can obtain city-by-city forecasts, conditions, warnings, and weather graphics for the United States. UM Weather allows users to receive live and daily pictures of weather conditions at over 700 locations in the United States and Canada. Users have access to over 150 weather sites (e.g., National Oceanic Atmospheric Administration, National Snow and Ice Data Center, and Midwestern Regional Climate Center) through UM Weather. Users can collect weather-related data from UM Weather at the link below.
4.2. Traffic Data Sources
Transportation-related data is quite accessible currently because multiple traffic data sources are available through the Internet. This section discusses some Web-based data sources that can provide information on traffic data (e.g., speed and volume) commonly used in traffic analyses. It should be noted that analysts are not limited to these data sources, and that traffic data exists for different locations around the county. The purpose here, however, is to show examples of the types of Web-based data sources that are available.
Data collection through the Internet can begin with search engines such as Google. A user can do a search for "Highway Performance Monitoring System." Doing this will provide the link for the FHWA's Highway Performance Monitoring System (HPMS) website. The HPMS database provides traffic data for statewide and nationwide highway systems. As part of HPMS, each State has permanent count stations, established in selected locations, that collect continuous 15-minute aggregated traffic counts. These traffic counts can be used in transportation planning models in order to obtain OD data for traffic analysis. Please refer to the HPMS website to access the available links to state HPMS websites. Link is provided.
Traffic engineers and researchers conducting weather-related traffic analyses involving the state of Virginia can collect traffic data from the Archived Data Management System (ADMS). ADMS provides data for such cases as planning and mobility performance measurement, decision support, and enhanced operational effectiveness (Center for Transportation Studies, 2010). A snapshot of the ADMS website is presented in Figure 4-4.
Figure 4-4. Archived Data Management System (ADMS) Homepage
Authorized ADMS users can access traffic count and speed data in 24 hour periods from Northern Virginia and the Hampton Roads region of Virginia. ADMS uses permanent count stations to obtain traffic count data. These permanent count stations archive traffic counts by speed bins for a particular time interval (e.g., from 6:00 to 6:15, 85 vehicles counted for 55-60 mph bin). ADMS also uses sensors (e.g., loop detectors) that are embedded in the road to collect averaged speed data for a specific time interval. This Web-based system allows users to specify routes and dates when collecting traffic information.
In addition to traffic information, weather data can be easily accessed and downloaded online from ADMS. Users can specify weather conditions when collecting ADMS weather information. Available weather conditions include drizzle, rain, fog, haze, snow, thunderstorm, mist and others (Archived Data Management System 2010). ADMS can be accessed by the following link.
Analysts in California can access transportation-related data from the internet through the California Department of Transportation Performance Measurement System (PeMS). From this website, seen in Figure 4-5, users can access historic traffic data which were collected from a time period spanning over 10 years. From the 25,000 detectors, users can access real-time traffic data for volume, speed, and delay.
Figure 4-5. Performance Measurement System (PeMS) Homepage
PeMS allows users to retrieve a wide range of transportation-related information from the California Department of Transportation and from local agencies, all in one stop. Such information includes: 1) incidents, 2) toll tags, 3) weight-in-motion, 4) vehicle classification, 5) census traffic counts, 6) lane closures, and 7) roadway inventory (California Department of Transportation, 2010). PeMS can be accessed by the link below.
A useful traffic data source for analysis in the Pacific Northwest is PORTAL which stands for Portland Oregon Regional Transportation Archive Listing. The PORTAL system contains a wide range of archived transportation-related data including the freeway loop detector data from Portland, OR to Vancouver, WA metropolitan area, incident data, freight data, transit data, and weather data (PORTAL, 2010). Figure 4-6 presents the homepage of PORTAL.
Figure 4-6. PORTAL Homepage
This data source provides daily statistics (e.g., total vehicle miles traveled, average travel time, and average travel speed) of highways in and around Portland, Oregon. An example of these daily statistics is shown in Figure 4-7 for I-5 North.
Figure 4-7. Daily Statistics for I-5 North
In conducting a microscopic analysis of traffic flow, users can use the live camera images from PORTAL to make visual observations of traffic flows on highways. Doing so could help users decide what needs to be accomplished to complete a successful analysis. For instance, users can conduct visual observations of headways during normal dry conditions and during inclement weather conditions. If they believe that headways significantly increase for inclement weather conditions from the visual observations then they can choose to calculate the actual changes in headways for their analysis. Data from PORTAL can be accessed at the following link.
Transportation-related analyses should be conducted using data sources with an abundance of information, such as that made available by the Minnesota Department of Transportation (Mn/DOT). This State DOT provides traffic volume information consisting of annual average daily traffic (AADT) and heavy commercial average daily traffic (HCADT) (Minnesota Department of Transportation, 2010). Figure 4-8 presents a snapshot of the Mn/DOT traffic data webpage.
Figure 4-8. Minnesota Department of Transportation Traffic
Minnesota also provides data obtained from continuous traffic counting sites that are located on interstates, municipal state-aid streets, and county-aid highways at different areas throughout the State. From these continuous traffic counting sites, users have access to data on volume, vehicle class, vehicle weight, and speed. Users can access the Minnesota Department of Transportation traffic data from the following link.
In some cases, using archived databases from State DOTs is not sufficient to conduct transportation-related analyses. This may be due to the location that is being studied. The State DOT may not contain essential traffic information that would be relevant to those traffic analyses. Therefore in those cases, the collection of field data may be a suitable option.
4.3. Intelligent Transportation Systems Data Sources
Intelligent Transportation Systems (ITS) allows for traffic data collection through the use of wireless and wired electronic devices. This section discusses those ITS technologies that can provide users with traffic data, such as travel time, traffic speed, and vehicle location.
We are in a time where technology is constantly advancing, and ITS takes traffic data sources and weather data sources to a new technological level. Connected vehicles, a US Department of Transportation initiative, is designed to create a network that connects vehicles to infrastructure and wireless devices. It is proposed that connecting these three elements will enhance safety and mobility and reduce the negative effects of transportation on the environment.
The mobility applications for connected vehicles have the potential to provide detailed, real-time traffic data about traffic conditions to transportation managers, allowing them to optimize transportation system performance. Such optimization includes adjusting traffic signals and sending out maintenance personnel in the event of an emergency. Along with providing traffic data, connected vehicles will provide information on current weather and road conditions in small coverage areas such as mile-by-mile or block-by-block (Row, 2010).
Some short-term traffic analyses may be performed using real-time travel data acquired from ITS. These analyses may provide a better assessment of current traffic operations because they were conducted with consistent traffic data (i.e., data being collected for the same time period). Therefore, these analyses will not have to rely heavily on historic traffic data.
By using ITS-generated data, traffic management agencies may have better weather coverage for a particular location. These agencies may be able to estimate the precipitation intensity through the use of wiper sensors on vehicles. The frequency of these wipers is key here. If wipers are set at a fast rate to clear the fallen precipitation from windshields of initiative’s probe vehicles, then agencies may to able to assume that vehicles in the study area are experiencing severe inclement weather (e.g., heavy rain or snow).
For more information on the connected vehicles initiative, please refer to the following link.
Transportation agencies can obtain traffic information from INRIX. However, this data is not free of charge. INRIX, shown in Figure 4-9, is a traffic services company that provides transportation-related information to businesses and individuals located in North America and Europe.
Figure 4-9 INRIX Homepage
Such information includes real-time and predictive traffic speed and travel times for major roadways (i.e., freeways and highways) and secondary roadways (i.e., arterials and side streets) (INRIX, 2010). Transportation-related information can be obtained for those who operate GPS-equipped vehicles (e.g., long-haul trucks and fleet vehicles) and who own consumer GPS-based devices (e.g., iPhone, iPad, Blackberry phones, and Android phones). For more information about the services provided by INRIX please refer to the following link.
When applicable, traffic information may be obtained from automatic vehicle location (AVL) technologies. This advanced traffic monitoring technology collects data from vehicles equipped with electronic tags (Tanikella et al., 2007). AVL allows for continuous collection of travel time data for each day of the year. Collecting travel time data in 24 hour periods is possible because AVL does not require manual recording of field data. Although AVL is heavily dependent on AVL devices (e.g., roadside antennas and roadside readers), it is a reliable source for travel time data collection.
Unlike AVL, Global Positioning System (GPS) involves locating objects that are not quite within reasonable reach. Transportation-related information (i.e., location and travel time) is collected from GPS-equipped vehicles that receive signals sent from the 24 satellites located in space (Turner et al., 1998). The collected data is sent to a storage computer located in a control center once the data collection process is completed. This method does not require making phone calls at checkpoints or manually recording information. Therefore, human error is smaller for data collection techniques that use GPS.
Travel time information collected from these ITS data sources can be essential in comparing the performance of a transportation facility during normal dry conditions and inclement weather conditions for weather-related transportation analyses. For additional information on AVL and GPS, please refer the Travel Time Data Collection Handbook shown below.
Engineers from Indiana Department of Transportation have raised the bar for the methods used to collect travel time data. Wasson, Sturdevant, and Bullock (2008) created a method that uses Bluetooth technology from cellular phones and other wireless devices to collect travel time data. Each wireless device has a unique digital signature which can be tracked by detectors located along the road. This method allows agencies to collect travel time for analysis purposes while also providing travel time information to motorists. For additional information on travel time data collection via Bluetooth please refer to Real-Time Travel Time Estimates Using Media Access Control Address Matching from the June 2008 issue of ITE Journal.
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United States Department of Transportation - Federal Highway Administration