Quality data are the foundation for making important decisions regarding the design, operation, and safety of roadways. While crash data have been a consistent element of highway safety analysis, in recent years there has been an increased focus on the combination of crash, roadway and traffic data to make more precise and prioritized safety decisions. By incorporating roadway and traffic data into safety analysis procedures, States can better identify safety problems and prescribe solutions to support their Highway Safety Improvement Programs (HSIP) and implement their Strategic Highway Safety Plans (SHSP).
A new generation of safety analysis tools and methods has been developed to help identify safety issues and provide recommendations for improvements. These safety analysis tools, such as the Highway Safety Manual (HSM), SafetyAnalyst, and the Interactive Highway Safety Design Model (IHSDM) all require quality roadway, traffic, and crash data to achieve the most accurate results. Integrating roadway and traffic data together with crash data can help agencies to make decisions that are fiscally responsible and to improve the safety of the roadway for all users.
Title 23 - Code of Federal Regulations, Part 924 on the Highway Safety Improvement Program (23 CRF 924) provides information on how safety data should be used (1). However, there are no details on specific roadway and traffic data elements that State agencies should be collecting, maintaining, and using to support their HSIPs and SHSPs. In 2011, the Federal Highway Administration (FHWA) Office of Safety released a guidance memorandum on the fundamental data elements that States should be collecting and incorporating into their safety analyses to support their HSIP and on what roadways they should be collected. The purpose of this report is to provide background information on why and how the guidance was developed, estimates of the costs of data collection, safety analysis tools and methods, and performance measures that should be considered and implemented to achieve quality safety data.
At a minimum, States should have a common relational location referencing system (i.e., geographic information system, linear referencing system, etc.) for all public roads. With the ability to locate crashes, States will be able to identify high crash locations on all public roads in the State. As States expand their inventories, this common relational referencing system will enable States to link these locations with roadway and traffic data.
Once a statewide location referencing system is in place, States should move towards collecting a set of fundamental roadway inventory data elements necessary to support an HSIP on all public roads. Recognizing that this may not be feasible for all States, States should prioritize collecting these elements on Federal-aid roads first and then expand to non-Federal-aid roads. Federal-aid roads include the National Highway System (NHS) and all functional systems excluding rural minor collectors and locals.
These fundamental data elements for HSIP (FDE/HSIP), as determined by an expert Technical Working Group (TWG), are shown in Table 1.
Table 1. FDE/HSIP Elements.
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FDE/HSIP Elements |
Definition |
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Roadway Segment |
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Segment ID* |
Unique segment identifier. |
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Route Name* |
Signed numeric value for the roadway segment. |
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Alternate Route Name* |
The route or street name, where different from route number. |
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Route Type* |
Federal-aid/NHS route type. |
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Area Type* |
The rural or urban designation based on Census urban boundary and population. |
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Date Opened to Traffic |
The date at which the site was opened to traffic. |
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Start Location* |
The location of the starting point of the roadway segment. |
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End Location* |
The location of the ending point of the roadway segment. |
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Segment Length* |
The length of the segment. |
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Segment Direction |
Direction of inventory if divided roads are inventoried in each direction. |
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Roadway Class* |
The functional class of the segment. |
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Median Type |
The type of median present on the segment. |
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Access Control* |
The degree of access control. |
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Two-Way vs. One-Way Operation* |
Indication of whether the segment operates as a one- or two-way roadway. |
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Number of Through Lanes* |
The total number of through lanes on the segment. This excludes turn lanes and auxiliary lanes. |
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Interchange Influence Area on Mainline Freeway |
The value of this item indicates whether or not a roadway is within an interchange influence area. |
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AADT* |
The average number of vehicles passing through a segment from both directions of the mainline route for all days of a specified year. |
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AADT Year* |
Year of AADT. |
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Intersection ID |
A unique junction identifier. |
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Location |
Location of the center of the junction on the first intersecting route (e.g., route-milepost). |
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| Intersection Type | The type of geometric configuration that best describes the intersection/junction. | |
| Date Opened to Traffic | The date at which the site was opened to traffic. | |
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Traffic Control Type |
Traffic control present at intersection/junction. |
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Major Road AADT |
The Annual Average Daily Traffic (AADT) on the approach leg of the intersection/junction. |
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Major Road AADT Year |
The year of the Annual Average Daily Traffic (AADT) on the approach leg of the intersection/junction. |
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Minor Road AADT |
The Annual Average Daily Traffic (AADT) on the approach leg of the intersection/junction. |
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Minor Road AADT Year |
The year of the Annual Average Daily Traffic (AADT) on the approach leg of the intersection/junction. |
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Intersection Leg ID |
A unique identifier for each approach of an intersection. |
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Leg Type |
Specifies the major/minor road classification of this leg relative to the other legs in the intersection. |
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Leg Segment ID |
A unique identifier for the segment associated with this leg. |
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Ramp ID* |
An identifier for each ramp that is part of a given interchange. This defines which ramp the following elements are describing. |
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Date Opened to Traffic |
The date at which the site was opened to traffic. |
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Start Location |
Location on the roadway at the beginning ramp terminal (e.g., route-milepost for that roadway) if the ramp connects with a roadway at that point. |
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Ramp Type |
Indicates whether the ramp is used to enter or exit a freeway, or connect two freeways. |
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Ramp/Interchange Configuration |
Describes the characterization of the design of the ramp. |
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Ramp Length |
Length of ramp. |
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Ramp AADT* |
AADT on ramp. |
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Ramp AADT Year |
Year of AADT on ramp. |
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*Highway Performance Monitoring System full extent elements required on all Federal-aid highways and ramps located within grade separated interchanges, i.e., National Highway System (NHS) and all functional systems excluding rural minor collectors and locals.
The FDE/HSIP are the basic set of elements an agency would need to conduct effective enhanced safety analysis. These are based on the elements needed to apply HSM roadway safety management procedures (Part B) using network screening analytical tools (such as SafetyAnalyst), are a subset of Model Inventory of Roadway Elements (MIRE), and duplicates many of the elements that States already collect for the Highway Performance Monitoring System (HPMS) on the full extent of Federal-aid roadways.
While the FDE/HSIP were selected in part based on the basic data requirements of existing tools such as such as the HSM and related SafetyAnalyst, they are not exclusive to these tools. FHWA recognizes that many States are developing analysis tools in-house that will help to support their HSIPs. The FDE/HSIP are a basic set of elements an agency would need to conduct effective enhanced safety analysis independent of the specific analysis tools used or methods applied. All States should be moving towards using analysis tools and having the FDE/HSIP available to utilize these tools, regardless of whether they are the tools developed through federal efforts or they are developed in-house.