LRS, ATIS, ARNOLD, and R&H

Arizona Transportation Information System (ATIS)

All Roads Network of Linear Referenced Data (ARNOLD)

Overview

Geographic Information Systems (GIS) are used to store the locations, shapes, and characteristics of Arizona's roadways. In ADOT, several acronyms tend to be used to describe Arizona's transportation GIS database: LRS, ATIS, ARNOLD, and R&H. While there are differences between each of these terms, they all generally refer to the same type of data. This page defines the different terms used and explains the similarities and differences between them.

Linear Referencing System (LRS)

A Linear Referencing System (LRS) is a method of storing and managing spatial data along a line. While an LRS can be used to manage data for any type of linear feature (e.g. roads, electrical lines, sewage and water pipes), this page focuses on using an LRS for roadway management.

An LRS stores the road characteristics separate from the centerline feature. The centerline feature is the key to an LRS as it accurately represents the spatial locations of road centerlines, with each centerline assigned a unique ID. In ADOT, the unique ID is referred to as the Route ID.

Road characteristics are stored in their own separate features, called Events, with each referring back to the centerline file to get their spatial locations and shapes. Each event layer stores the Route ID and the measurements from where the feature occurs on the centerline in relation to the beginning of the route. ADOT refers to these measurements as "Measures" and report them in miles from the start of the centerline (see example below).

Figure 2: LRS Centerline and Event Layers

Example

Interstate 10 begins in ADOT's LRS at the Arizona-California border west of Ehrenberg (see Figure 3). When new asphalt concrete was poured along a two-mile stretch for that section of roadway, a record was added to the event layer "Travel Surface Type" that recorded the type of asphalt concrete as well as the Route ID (for I-10, the route ID is "I 010"), the beginning measure (measure 0), and the ending measure (the exact end of the project was 2.005 miles from the border). Those three pieces of information were all that were needed for the LRS to know exactly where the pavement change occurred as well as how to draw the road shape for the Travel Surface Type event layer since the shape was already available in the centerline feature.

Figure 3: Example of route and Measure

Measures vs Mileposts

Mileposts are markers placed at one-mile increments along the side of a road. While they are used to get approximate locations on a road, they are not accurate, especially when measurements less than a foot are required. Changes to a road's length or shape, such as a curved road being straightened, do not typically affect milepost markers since the cost to update each milepost marker, ramp marker, and signage would be significant.

Measures are used internally in ADOT's GIS system, also known as the Arizona Transportation Information System (ATIS). Measures are more accurate than mileposts and are updated anytime a road's length or shape changes.

Advantages Of An LRS

The advantage of using an LRS is its improved data management ability over a traditional GIS method, which would store all of the road attributes as table columns in the centerline feature layer. When mapping roadway characteristics, instead of having to manually draw each feature (tracing the roadway shape accurately each time), an LRS only requires two to three pieces of information in order to accurately locate and draw the feature.

- - For points features, such as road signs, the LRS needs the Route ID and the measure where the sign is on the road
  - For line features, such as speed limit zones, the LRS needs the Route ID, measure where the feature starts (beginning measure), and measure where the feature ends (ending measure)

In addition, having the attributes in their own separate layers means making changes to one attribute does not affect the others.

Data Analysis Using An LRS

A downside of an LRS is its ability to allow for data analysis. When comparing two or more event layers is needed to analyze a road network, such as if the number of lanes on a road need to be increased to accommodate recent increases in traffic, it is easier to have a single centerline feature layer with the road attributes combined. The process to collapse the centerline and event layers into a single feature is called an Overlay.

LRS Before Overlay

After Overlay

Arizona Transportation Information System (ATIS)

The Arizona Transportation Information System (ATIS) refers to Arizona's transportation LRS. It not only specifies that it's a transportation LRS, as opposed to an LRS for managing other data like water and sewer pipes, it also identifies that its Arizona's transportation LRS, in contrast with another state DOT's LRS.

ATIS is a spatial dataset that represents the centerlines for Arizona roads. While the dataset does contain centerlines for all roads open to public travel, it may also include roads restricted from public travel, like gated communities and service roads. ATIS also includes separate event layers for various road characteristics, such as pavement and traffic data, with each referring back to the centerline file for spatial location information.

Figure 4: ATIS Centerlines

Importantly, ATIS is the primary source of data for several state and federal reports, including the federal Highway Performance Monitoring System (HPMS) report, Certified Public Mileage (CPM) report, Model Inventory of Roadway Events (MIRE) report, and the Arizona State Highway System Log.

For more details about ATIS, its history, and importance, refer to the storymap Arizona Transportation Information System (ATIS).

All Roads Network of Linear Referenced Data (ARNOLD)

The Federal Highway Administration (FHWA) refers to their LRS as the All Roads Network for Linear Referenced Data (ARNOLD). Specifically, ARNOLD refers to the centerline file that represents all public roads in the nation. It is update each year by combining the centerline data collected from each state, District of Columbia (DC), and Puerto Rico through the Highway Performance Monitoring System (HPMS) report.

ARNOLD specifically refers to the centerline file submitted in HPMS. Roadway characteristic data are submitted in separate HPMS reports as tables but include route ID and measures that allow each table to refer to ARNOLD when spatial locations are needed. Note, in ARNOLD, measures are referred to as "milepoints."

For more details about ARNOLD, refer to the ARNOLD Reference Manual.

Roads and Highways (R&H)

Roads and Highways, abbreviated as R&H or RnH, refers to the software and database system used to manage and store Arizona's LRS centerline and event data. R&H is a product of Esri and was designed to specifically manage road network data using Route ID and measure information. The software includes tools to help convert LRS data into datasets better suited for roadway analysis - a process known as an Overlay.

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