What Is GIS?

Geographic Information Systems (GIS) is a field that provides the ability to capture and analyze spatial and geographic data in a visual way. This field incorporates geographical features with tabular data, thus it can be mapped and analyzed to asses real world problems. GIS can be used in nearly any discipline but most important to ADOT is its use in transportation.

Understanding what GIS is allows you to imagine all the capabilities GIS has to offer. This story map will describe what GIS is and what it is used for, and how ADOT specifcally leverages GIS.

Using GIS might seem overwhelming with all the new terminology but if you want to easily answer questions like...

...then GIS can help. At its core, GIS allows for the analysis of data with the added dimension of location. This is why GIS is more powerful than just using a spreadsheet! Users can determine spatial relationships not readily available in a table in addition to the conventional data analysis availabile in spreadsheets like summaries and totals.

People are more familiar with GIS than they realize - we see and use maps daily, and most topics in our life have some sort of location based information whether it's an address, a latitude and longitude, or a road and milepost. The simple question of WHERE opens up a plethora of opportunities for improved analysis.

The non-spatial (or tabular) portion of GIS data is typically referred to as attribute data. Attribute data is the additional information about each of the spatial features. This type of data is represented as points, lines and polygons. This could be a polygon feature that represents land ownership, and the attribute data shows the different owners. The ability to overlay these data elements is what makes GIS such an innovative tool. GIS technology allows you to tell a story with data using computer cartography. It can be used with spatial and statistical methods to analyze attribute and geographic information.

Transportation data is inherently geospatial. Regardless of the specific data, whether it be pavement quality or speed limit, the data is tied to the geographic feature that is a roadway. Within GIS transportation data, there are a few pieces of important GIS data; Linear Referencing System (LRS), Roadway Characteristics, Transportation System Assets, Traffic Data, Transportation Safety, and Federal Reporting for Transportation. 

LRS is a road centerline network that uses various methods for managing and locating geospatial information along a linear feature. Fundamentally the LRS is a route with measures along the route. There are other methods to reference data off of including addressing, milepost or referent offset, engineering stationing, crossing routes, and other fixed locations as referents.

LRS is crucial for managing the vast and varied data collected and maintained by a DOT. It is the framework for all DOT geospatial data and the basis of determining one source of truth. The LRS also allows for integration of other data systems into a unified network. For example, the integration of pavement data onto the LRS allows for greater analysis.

Roadway Characteristics are all of the information about the roadways itself. This includes:

These characteristics are gathered using a variety of methods. Methods include construction plan review. This involves the reading of AsBuilt documents to pull out data.  Visual analysis such as looking at the imagery of a roadway to determine the characteristics. Field validation analysis which involves a sample size of roadway characteristics data by going in the field to determine the characteristics of the roadway. Video log extraction which involves collecting data from a vehicle’s perspective, such as speed limit zones.   

Transportation Asset Management are the details and attributes attached to the roadway. These are attributes that are not the actual roadway, but important to identify attributes on the roadway. This includes: 

• Pavement
• Bridges
• Culverts
• Right-of-Way
• Guard Rails/Barriers
• Signs
• Roadway Lighting
• Sound Walls
• Pavement Marking (Striping)
• Rumble Strips
• Utilities
• Fiber
• Landscaping (Highway Beautification)

Gathering this information is similar to the gathering of the Roadway Characteristics data. Managing this data in a GIS allows for improved planning and cost reduction.  Having an inventory of this data allows decision makers to make informed decisions.  Transforming data into actionable information.

Traffic data is integral to the transportation industry. Traffic data includes: 

Traffic volumes is an incredibly dynamic data set due to it changing on a minute to minute basis.  Tracking trends in volumes by day of the week and time of the year improves planning. Many other elements of traffic data are gathered for transportation GIS purposes. This includes vehicle classification such as car, motor cycle, semi-truck, etc.  This information is useful for a variety of applications such as pavement quality deterioration over time. Population growth is used to predict changes in traffic volumes, which in turn is used to help plan for the expansion of the highway network. 

Traffic data is gathered from traffic counting technologies.  This data is stored and managed in MS2 Soft Traffic Data Modeling System (TDMS). This allows both the state and local agencies to manage their traffic data and share it with other agencies and the state. To read more about MS2, click here. Traffic is collected by physical devices called tubes that are on the road that count traffic as cars drive over them. These then report traffic data for analysis.

Transportation Safety is a huge concern for ADOT.  ADOT wants all of Arizona’s drivers to get home safely. Accidents do happen and this is tracked in GIS as point data that represents vehicle crashes. Safety data must be reported to the federal government for the Model Inventory of Roadway Elements (MIRE), which uses data from roadway assets and characteristics to determine the safety status of a roadway. To enhance analysis looking at intersections and intersection zones (i.e. before and after an intersection) is vital to safety mitigation. The reason being is that many vehicle crashes occur in or near an intersection.  With this level of detailed data, hot spots can be identified and plans put in place to reduce injury.

Federal Reporting is a huge part of transportation GIS. Federal Reporting drives the need for data collection and reporting by states. The customer is the Federal Highway Administration (FHWA) who apportion funds to each state transportation department. Major reports for transportation data include:

• Highway Performance Monitoring System (HPMS): HPMS is a report due to FHWA each year that reports on all roadway data from the number of lanes on a road, to pavement quality. For more information please visit:  https://www.fhwa.dot.gov/policyinformation/hpms/fieldmanual/ 
• All Roads Network of Linear Referenced Data (ARNOLD): This is a new requirement for states. Each state must maintain and report spatial representation for all public roads in the state. For more information please visit:  https://www.fhwa.dot.gov/policyinformation/hpms/arnold.cfm 
• Certified Public Mileage (CPM) (A requirement for the HPMS submission): CPM is required for reporting and is the total number of public miles that are, open to the public, not gated or restricted, passable by a standard two passenger car and include Bureau of Indian Affairs (BIA) lands. This must be given to FHWA with a letter, signed by the director of ADOT and the state governor. For more information please visit:  https://www.fhwa.dot.gov/policyinformation/hpms/arnold.cfm 
• Model Inventory of Roadway Elements (MIRE): MIRE is closely related to HPMS data items but is greatly expanded to include both on and off the state owned system. MIRE is focused on safety related data items. For more information please visit:  https://safety.fhwa.dot.gov/rsdp/mire.aspx 
• The following are deliverables produced from these Federal Reports:
• State Highway Log: The state highway system is a breakdown of mileage for the state owned roads. This includes two distinctions in mileage, centerline miles and maintenance lane miles. Click here to read about the difference between those mile types. 
• Extent and Travel Report (Part of the HPMS submission): This is a report created by FHWA based on data submitted for HPMS. It breaks down the mileage by Functional Classification, Lane Miles, Centerline Miles and Vehicle Miles Travelled. This is also broken into Urban and Rural cities. 
• Pavement Report Card (Part of the HPMS submission): Pavement quality is rated in ‘Good’, ‘Fair’ and ‘Poor’, for 2 different metrics for rating. Each of these metrics are used to detect the amount of ‘Good”, ‘Fair’ and ‘Poor’ quality. 

ADOT uses GIS to gather and analyze roadway information throughout the state for reporting purposes. Using ESRI software to analyze and compile roadway data allows ADOT to report on all data items required for HPMS. Transforming data into actionable information is vital.

ADOT leverages a number of tools to transform GIS data. AZGeo is this statewide data hub that houses state agency authoritative geospatial data. AZGeo also has a number of applications. One of which is the Centerline Unification and a data supply chain ticketing application. This application allows for the gathering of local agency centerline data for integration into ADOT’s LRS.  

Another application is the Arizona’s Functional Classification Change Request tool. This application helps to digitize a once paper based request process for upgrading or downgrading roadway functional classification. The functional classification is important to local agencies since it determines funding for roadway maintenance. These tools allow local agencies to validate and requests changes to the GIS data at AZDOT. 

To manage traffic count data, the state utilizes a software called MS2. This allows both the state and local agencies to manage their traffic data and share it with other agencies and the state. To read more about MS2, click  here .

With all of this geospatially enabled data the ability to tell a story with it is incredibly important. This is done in a variety of ways from paper maps, online interactive maps and dashboards.  Each are utilized to share complex data with data users in a simple and easily filtered way. Dashboards for example allow users to filter data to answer questions for data driven decisions. 

GIS is an incredibly useful tool and pathway for all kinds of fields. Arizona DOT utilizes GIS in many ways and continues to use GIS to find innovative solutions. To read more about ADOT’s GIS usage, see the story maps below. 

 Arizona Transportation Information System (ATIS) 

 ARNOLD and the Data Supply Chain 

 Certified Public Mileage (CPM) 

 Highway Performance Monitoring System (HPMS)