Improved More Better Fewer

Data Informed Targeted Fatalities

Collection Decision Safety & Serious

& Analysis Making Investment Injuries

Roadway Safety Data Program

NEW HAMPSHIRE’S INTERSECTION INVENTORY

ROADWAY SAFETY DATA AND ANALYSIS

CASE STUDY

FHWA-SA-15-087

Prepared for

Federal Highway Administration

Office of Safety

Roadway Safety Data Program

http://safety.fhwa.dot.gov/rsdp/

October 19, 2015
NEW HAMPSHIRE’S INTERSECTION INVENTORY

Notice

This document is disseminated under the sponsorship of the U.S. Department of

Transportation in the interest of information exchange. The U.S. Government assumes no

liability for the use of the information contained in this document. 

The U.S. Government does not endorse products or manufacturers. Trademarks or

manufacturers’ names appear in this report only because they are considered essential to the

objective of the document. 

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve

Government, industry, and the public in a manner that promotes public understanding. 

Standards and policies are used to ensure and maximize the quality, objectivity, utility, and

integrity of its information. FHWA periodically reviews quality issues and adjusts its programs

and processes to ensure continuous quality improvement.

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ACKNOWLEDGEMENTS

The Roadway Safety Data Program team would like to thank the following individuals who

graciously provided information needed to develop this case study. 

Name Title Department Email/Phone#

Tim Harmon Assistant Highway 

Safety Engineer

New Hampshire 

DOT

tharmon@dot.state.nh.us 

603.271.2524 

Michelle Marshall Highway Safety Engineer New Hampshire 

DOT

memarshall@dot.state.nh.us

603.271.1407 

New Hampshire Department of Transportation

7 Hazen Drive

Concord, NH 03303-0483 

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TABLE OF CONTENTS 

INTRODUCTION................................................................................................................. 1

BACKGROUND.................................................................................................................... 1

OBJECTIVE............................................................................................................................ 1

AUDIENCE............................................................................................................................ 2

DEVELOPING THE INTERSECTION INVENTORY ....................................................... 2

APPLICATION AND AVAILABILITY OF THE INTERSECTION INVENTORY........ 6

RESULTS ............................................................................................................................... 7

Benefits ........................................................................................................................... 7

Lessons Learned ............................................................................................................ 7

Next Steps...................................................................................................................... 8

Funding ........................................................................................................................... 8

Personnel........................................................................................................................ 8

REFERENCES........................................................................................................................ 9

AGENCY CONTACT INFORMATION............................................................................. 9

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List of Figures

Figure 1: Image of Data Collection Through GIS-based Data Entry Forms. ................. 5

Figure 2: Data Entry Forms for Intersection and Intersection Legs. .............................. 6

List of Tables

Table 1. Intersection Inventory Elements Requested by NHDOT.................................. 4

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ACRONYMS

AADT Average Annual Daily Traffic

FHWA Federal Highway Administration

GIS Geographic Information System

HSIP Highway Safety Improvement Program

HSM Highway Safety Manual

IHSDM Interactive Highway Safety Design Model

LRS Linear Referencing System

MIRE Model Inventory of Roadway Elements

MIS Management Information System

NHDOT New Hampshire Department of Transportation

RPC Regional Planning Commission

SPF Safety Performance Function

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EXECUTIVE SUMMARY

One of the major challenges transportation agencies face when trying to address intersection 

safety is not having a sufficient intersection inventory that provides location, operations, or 

geometrics of the intersections. In 2010, the Federal Highway Administration (FHWA) released 

the Model Inventory of Roadway Elements (MIRE), which is a recommended list of roadway and 

traffic volume data elements important to safety management and analysis. The New Hampshire 

Department of Transportation (NHDOT) was one of two States selected by FHWA to 

participate as a Lead Agency in the MIRE Management Information System (MIS) effort. FHWA 

conducted the MIRE MIS Lead Agency Program pilot project to test the feasibility of collecting, 

storing, and integrating MIRE data into an MIS and then linking roadway inventory data with crash 

and other relevant data for safety analyses.

NHDOT chose to focus their data collection effort on the acquisition of additional intersection 

elements to expand its use of AASHTOWare Safety AnalystTM primarily to support network 

screening analyses. After NHDOT completed data collection and integrated the data into the 

system, they now use the inventory for evaluating roadway safety countermeasures and for 

performing economic analysis. The intersection inventory supports better safety analysis using 

data specific to New Hampshire’s roadway network instead of default values or national averages. 

New Hampshire has benefitted from the state-specific data by targeting their spending by 

comparing sites and prioritizing locations with greater potential for improvement.

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INTRODUCTION

In 2013, there were 30,057 fatal crashes in the United States; almost one-fourth of those 

occurred at an intersection or were intersection-related (1). One of the major challenges 

transportation agencies face when trying to address intersection safety is not having a sufficient 

intersection inventory that provides information on the location, operations, or geometrics of 

the intersections. Quality data are the foundation for making important decisions regarding the 

design, operation, and safety of roadways. With the recent development of more advanced 

safety analysis tools, including AASHTOWare Safety AnalystTM, Interactive Highway Safety 

Design Model (IHSDM), and the Highway Safety Manual (HSM), many agencies are seeing the 

value of better roadway data. The more detail a State or local agency knows about its roadways 

(including intersections), the better it can allocate its resources to identify problem locations, 

diagnose issues, prescribe appropriate countermeasures, and evaluate the effectiveness of those 

countermeasures. This process can lead to a more successful safety program supported by 

data-driven decision-making, to help improve the safety of roadways and ultimately save lives 

(2). The purpose of this case study is to describe the challenges and successes in developing and 

using the intersection inventory in New Hampshire.

BACKGROUND

In 2010, the Federal Highway Administration (FHWA) released the Model Inventory of 

Roadway Elements (MIRE), which is a recommended listing of roadway and traffic volume 

elements important to safety management, and includes a data dictionary for each element (3). 

MIRE Version 1.0 includes 202 elements grouped into three broad categories: roadway segment 

descriptors, roadway alignment descriptors, and roadway junction descriptors. FHWA 

conducted the MIRE Management Information System (MIS) Lead Agency Program pilot project 

to test the feasibility of collecting, storing, and integrating MIRE data into an MIS and then 

linking roadway inventory data with crash and other relevant data for safety analyses. The New 

Hampshire Department of Transportation (NHDOT) was one of two States selected by 

FHWA to participate as a Lead Agency in the MIRE MIS effort. The objective of the Lead 

Agency Program was to assist volunteer agencies in the collection, storage, and maintenance of 

MIRE data and to incorporate those data into their safety programs. Each Lead Agency chose 

what MIRE elements it would collect through the program. NHDOT chose to focus their data 

collection effort on the acquisition of additional intersection elements to expand its use of 

AASHTOWare Safety AnalystTM and to improve the maintenance of their safety data through 

use of automated geographic information system (GIS) tools to update the inventory on an 

annual basis.

OBJECTIVE

NHDOT developed the intersection inventory to accomplish the following: 

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NEW HAMPSHIRE’S INTERSECTION INVENTORY

• Assist safety engineers managing the State’s roadway network.

• Provide a high level of detail for intersection attributes.

• Enhance the State’s implementation of Part B of the HSM utilizing AASHTOWare 

Safety AnalystTM to: 

o Compare intersections with similar characteristics and identify intersections 

that have potential for safety improvement.

o Select and prioritize projects with more efficiency and therefore, improve 

allocation of funds.

o Support before-after analysis to quantify the safety benefit of implemented 

projects.

AUDIENCE

This case study applies to the following audiences: 

• State Departments of Transportation: Safety Engineering, Design, Planning, Maintenance, 

GIS, and Asset Management Units.

• Local and Regional: City and County Public Works/Engineering/Transportation 

Departments, Metropolitan Planning Organizations, and Regional Planning Commissions.

• Local and Tribal Technical Assistance Programs.

• Consultants and private industries involved with safety.

DEVELOPING THE INTERSECTION INVENTORY

NHDOT GIS staff manages the State’s linear referencing system (LRS), which includes all 

Federal, State, local, and private roads in the State. The LRS includes a defined set of 

approximately 40 road centerline attributes, and a node layer representing roadway junction 

locations. Each node has a unique identifier associated with it, but includes no attribute 

information. Prior to the MIRE MIS Lead Agency Program project, NHDOT developed a 

preliminary list of State-owned intersections using the node layer from the LRS and developed a 

methodology for relating the State’s LRS road centerline attributes to the State-owned 

intersection locations.

Although NHDOT had a basic inventory of the State-owned intersections, their LRS system did 

not contain some critical intersection element information (such as traffic control type), forcing 

the agency to assign default element values within AASHTOWare Safety Analyst. NHDOT 

began licensing AASHTOWare Safety AnalystTM in 2009 and used the software’s data 

requirements list, which are similar to the MIRE Fundamental Data Elements Subset, to define 

which intersection elements (both intersection and intersection leg elements) to prioritize in 

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the MIRE MIS intersection data collection effort. Table 1 lists the intersection inventory 

elements included as part of New Hampshire’s MIRE MIS effort. These elements include all of 

the required AASHTOWare Safety AnalystTM elements for intersections and intersection legs,

along with some of the optional elements. NHDOT prioritized collecting data on State/State 

intersections (approximately 1,500), followed by State/local intersections (approximately 8,800), 

and then local/local intersections (approximately 30,750) (2). Data collection associated with 

the MIRE MIS effort was limited to the State/State and State/local intersections. 

The work associated with the MIRE MIS effort involved a two-part process. First, a custom GIS 

toolbar, designed to integrate the State’s LRS with the intersection inventory, prepopulated 

about a third of the intersection/intersection leg attributes. Second, data collectors populated 

the remaining intersection elements not harvested from the State’s LRS and verified the 

prepopulated elements. Data collectors accessed online aerial imagery and street-level images, 

and entered the element data using customized data entry forms developed as part of the GIS 

toolbar (Figure 1 and Figure 2). NHDOT used electronic data entry forms to enforce data 

quality standards through validation and consistency checks. After the data collection, traffic 

engineers field-verified a sample of the intersections as part of the QA/QC process.

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Table 1. Intersection Inventory Elements Requested by NHDOT.

Intersection Elements Intersection Leg Elements

Intersection ID Intersection ID

Location System Leg ID

Route Type Type 

Route Name Location System

County Route Type

Major Road MP Route Name

Minor Road Location System County 

Minor Road Route Type Milepost/Distance

Minor Road Route Name Influence Zone

Minor Route MP Direction of Leg

Agency Site Subtype Number of Thru Lanes

GIS Identifier Number of Left Turn Lanes

Major Road Name Number of Right Turn Lanes

Minor Road Name Median Type

Major Road Direction Left Turn Phasing

Begin Influence Zone (Major & Minor) Speed Limit

End Influence Zone (Major & Minor) Turn Prohibitions

District Operations

City Town Approach Volume 

Jurisdiction Right Turning Movement Count

Area Type Thru Turning Movement Count

Intersection Type Left Turning Movement Count

Traffic Control Type

Offset Intersection

Offset Distance

Growth Factor

Date Open to Traffic

Corridor

Major Road Annual Average Daily Traffic 

(AADT)

Minor Road AADT

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Figure 1: Image of Data Collection Through GIS-based Data Entry Forms.

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Figure 2: Data Entry Forms for Intersection and Intersection Legs.

APPLICATION AND AVAILABILITY OF THE INTERSECTION INVENTORY

NHDOT’s Bureau of Highway Safety uses the inventory as data input into AASHTOWare 

Safety AnalystTM, primarily for conducting network screening analyses—the process of studying 

safety conditions on roadways to compare sites and prioritize locations with greater potential 

for improvement. NHDOT also uses the inventory for evaluating their roadway safety 

countermeasures and for performing economic analysis such as evaluating the benefit/cost ratio 

of proposed or implemented countermeasures. NHDOT also finds the inventory useful when 

submitting annual reports for the Highway Safety Improvement Program (HSIP). The HSIP 

report requires State DOTs to provide project tracking information (e.g., track performance 

measures, project starts by year, and transportation fund allocation). 

The intersection inventory is available to all NHDOT staff and local agencies; however, the 

integration and use of the inventory by other NHDOT divisions and external partners is a work 

in progress. All Regional Planning Commissions (RPCs) are using the inventory as a part of 

AASHTOWare Safety AnalystTM, but some municipal agencies may not know the inventory 

exists or that it contains information that would be useful to them. NHDOT is planning to 

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work with the State’s GIS clearinghouse to make the intersection inventory more publicly 

available.

RESULTS

Benefits

NHDOT identified the following benefits of the MIRE MIS Project and the intersection 

inventory: 

• The intersection inventory enhances NHDOT’s implementation of Part B of the HSM

using AASHTOWare Safety AnalystTM.

• The intersection inventory supports better safety analyses using data specific to New

Hampshire’s roadway network instead of relying on default values or national averages.

• The intersection inventory allows NHDOT safety engineers to make data-driven

decisions and simplifies federal reporting requirements.

• The data maintenance tools developed as part of the intersection inventory reduce staff

time spent on updating the inventory, allowing more time to be spent analyzing and

reporting on the data.

• NHDOT does not need specialized GIS staff to edit their intersection inventory because

the user-friendly data entry forms simplify the data input process and eliminate data

entry errors.

Lessons Learned

NHDOT noted that the initial intersection inventory was relatively easy to develop using its 

LRS and available roadway attribute data with GIS and Oracle. NHDOT was able to develop 

automated GIS processes for updating their intersection inventory based on their annual LRS 

update schedule. Agencies wanting to implement AASHTOWare Safety AnalystTM must have an 

accurate way to locate their crashes on their LRS. Agencies must be able to link crash data and 

crash locations to the road network, as well as intersection locations. NHDOT already had a 

system in place, which saved time and money for all users.

NHDOT recommends agency staff conduct an inventory of existing data elements within their 

Department as the first step in developing an intersection inventory, and then assess which 

elements still need to be collected or derived from existing elements.

NHDOT noted that agencies seeking to develop an intersection inventory should not wait for 

perfection—meaning collecting and storing every attribute for the entire roadway network in 

the State—before using the data for analyses. The roadway network is constantly changing and 

the database will need updating. NHDOT prioritized their collection efforts by first collecting 

data for State-maintained roads then local roads, and concentrating on required elements. 

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Optional elements were not collected unless they could be derived from other available data. 

NHDOT learned that the data supporting the inventory (e.g., an advanced GIS roadway 

inventory, with geometric topology rules and established QA/QC procedures) should be 

accurate and reliable because the process of updating and adding data will be easier.

Next Steps

NHDOT desires to improve its estimation of AADT on local roads. Only five percent of local 

roads have traffic counts in New Hampshire. With crashes and traffic volumes as the primary 

factors in AASHTOWare Safety AnalystTM Safety Performance Functions (SPFs), estimated 

traffic volumes decrease the accuracy of the analysis. Currently, local intersection data is not as 

useful because it is of poorer quality than the State data. NHDOT often removes local 

intersections from analyses because of the issues with AADT; however, the data are still useful 

for HSIP reporting and for calculating statistics not tied to traffic volumes. Having reliable local 

AADT (e.g., roads that intersect state routes, urban local roads that make up smaller city 

streets) would help NHDOT conduct a more complete analysis of the entire State’s roadway 

network. 

NHDOT would also like to improve its database of driveways and private roadways. 

Intersections with major driveways (e.g., large shopping centers) can carry large amounts of 

traffic; often more than many intersections between state routes. While many private roads 

exist in the road inventory, NHDOT’s LRS does not contain detailed attribute information on 

private roads and driveways even though these roads may have high traffic volumes. As a result, 

State/private road intersections are not yet included in the State’s intersection inventory. 

Funding

The entire MIRE MIS effort, including the development of the intersection inventory and the 

traffic dataset, cost approximately $210,000, which FHWA funded through the MIRE MIS Lead 

Agency program (2). The collection of the State/State and State/local intersection elements 

took approximately 1,600 hours to complete, and relied heavily on the use of technical level 

support staff. Development of the GIS toolbar, with the data collection forms and intersection 

maintenance tools, took an additional 200 hours to complete. Since the MIRE MIS Project, 

NHDOT has used approximately $10,000 in HSIP funds to enhance the inventory, which 

includes an intersection inventory manual documenting the uses of the GIS toolbar and data 

entry forms. 

Personnel

The Bureau of Highway Design’s Safety Section, consisting of two staff members, utilizes and

manages the intersection inventory. The Bureau of Planning and Community Assistance 

manages NHDOT’s LRS, with 10 GIS staff members.

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REFERENCES

The following resources were consulted in development of this case study:

1. National Highway Traffic Safety Administration, Fatality Analysis Reporting System

(FARS) Encyclopedia, Accessed online 11 May 2015,

http://www-fars.nhtsa.dot.gov/QueryTool/QuerySection/SelectYear.aspx

2. Fiedler, R.; N. Lefler; J. Mallela; D. Abbott; D. Smelser; and R. Becker. MIRE MIS Lead

Agency Data Collection Report. Federal Highway Administration, FHWA-SA-13-008,

Washington, D.C., March 2013,

http://safety.fhwa.dot.gov/rsdp/downloads/leadagencydatacollection.pdf

3. Lefler, N.; F. Council; D. Harkey; D. Carter; H. McGee; and M. Daul. Model Inventory of

Roadway Elements – MIRE, Version 1.0. Federal Highway Administration, FHWA-SA-10-

018, Washington, D.C., October 2010,

http://safety.fhwa.dot.gov/tools/data_tools/mirereport/

4. NHDOT Highway Safety Section – Tim Harmon. Telephone Interview. April 30, 2015.

AGENCY CONTACT INFORMATION

Michelle Marshall

Highway Safety Engineer

memarshall@dot.state.nh.us

(603) 271-1407 

New Hampshire Department of Transportation

Division of Project Development – Bureau of Highway Design

7 Hazen Drive

Concord, NH 03302-0483 

Tim Harmon

Assistant Highway Safety Engineer

tharmon@dot.state.nh.us

(603) 271-2524 

New Hampshire Department of Transportation

Division of Project Development – Bureau of Highway Design

7 Hazen Drive

Concord, NH 03302-0483 

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