Roadway Safety Data Program

TENNESSEE’S HORIZONTAL CURVE DATABASE

ROADWAY SAFETY DATA AND ANALYSIS

CASE STUDY

FHWA-SA-16-048

Prepared for

Federal Highway Administration Office of Safety

Roadway Safety Data Program

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

Improved

Data

Collection

& Analysis

More

Informed

Decision

Making

Better

Targeted

Safety

Investment

Fewer

Fatalities

& Serious

Injuries

April 21, 2016
TENNESSEE’S HORIZONTAL CURVE DATABASE

ii

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.

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and processes to ensure continuous quality improvement.
TENNESSEE’S HORIZONTAL CURVE DATABASE

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TECHNICAL DOCUMENTATION PAGE

1. Report No.

FHWA-SA-16-048

2. Government Accession

No.

3. Recipient's Catalog No.

4. Title and Subtitle

Tennessee’s Horizontal Curve Database: Roadway Safety Data and Analysis Case

Study

5. Report Date

April 21, 2016

6. Performing Organization Code

7.Author(s)

Robert A. Scopatz and Matthew Albee

8. Performing Organization Report No.

9. Performing Organization Name and Address

VHB

8300 Boone Blvd., Suite 700

Vienna, VA 22182-2626 

10. Work Unit No.

11. Contract or Grant No.

DTFH61-05-D-00024 (VHB)

12. Sponsoring Agency Name and Address

Federal Highway Administration Office of Safety

1200 New Jersey Ave., SE

Washington, DC 20590

13. Type of Report and Period

Draft Report, Month Year – Month

Year

14. Sponsoring Agency Code

FHWA

15. Supplementary Notes

The contract manager for this report was Esther Strawder.

16. Abstract

In 2012, The Tennessee Department of Transportation (TDOT) accomplished its initial data collection for 

its entire roadway network, which includes all interstates, state highways, arterials, collectors, and local 

roads. With these data, TDOT created a horizontal curve database with approximately 40,000 miles of 

roadways with curves, which is housed in the Tennessee Roadway Information Management System 

(TRIMS)—a client-server application that allows TDOT to capture, maintain, and view critical roadway 

data. TDOT uses the horizontal curve database to provide quick, data-derived answers to public concerns, 

make data-driven decisions, quantify potential benefits from both systemic and spot improvements, and 

compare curves with similar characteristics to help prioritize projects.

17. Key Words:

safety data, roadway inventory data, traffic data,

data collection, crash data

18. Distribution Statement

No restrictions.

19. Security Classif. (of 

Unclassified

this report) 20. Security Classif. (of 

page) Unclassified

this 21. No. 

7

of Pages 22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed pages authorized
TENNESSEE’S HORIZONTAL CURVE DATABASE

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TABLE OF CONTENTS

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

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

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

AUDIENCE.................................................................................................... 1

THE HORIZONTAL CURVE DATABASE ................................................ 2

APPLICATIONS OF THE HORIZONTAL CURVE DATA ..................... 3

RESULTS ....................................................................................................... 4

FUNDING ...................................................................................................................... 4

BENEFITS ...................................................................................................................... 5

BARRIERS AND HOW THEY WERE OVERCOME.................................................5

LESSONS LEARNED.................................................................................................... 5

NEXT STEPS................................................................................................................. 5

AGENCY CHARACTERISTICS.................................................................. 6

ORGANIZATIONAL STRUCTURE........................................................................... 6

PERSONNEL ................................................................................................................. 6

REFERENCES................................................................................................ 7

AGENCY CONTACT INFORMATION .................................................... 7
TENNESSEE’S HORIZONTAL CURVE DATABASE

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ACRONYMS 

AADT Annual average daily traffic

CMF Crash Modification Factor

GIS Geographic Information System

GPS Global Positioning System

HFST High Friction Surface Treatment

HSM Highway Safety Manual

LOS Level of Service

LRS Linear Referencing System

MPO Metropolitan Planning Organization

RFP Request for Proposal

RPO Rural Planning Organization

SPF Safety Performance Function

TDOT Tennessee Department of Transportation

TRIMS Tennessee Roadway Information Management System
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EXECUTIVE SUMMARY

In 2012, The Tennessee Department of Transportation (TDOT) accomplished its initial data 

collection for its entire roadway network, which includes all interstates, state highways, 

arterials, collectors, and local roads. With these data, TDOT created a horizontal curve 

database with approximately 40,000 miles of roadways with curves, which is housed in the 

Tennessee Roadway Information Management System (TRIMS)—a client-server application that 

allows TDOT to capture, maintain, and view critical roadway data. TDOT uses the horizontal 

curve database to provide quick, data-derived answers to public concerns, make data-driven 

decisions, quantify potential benefits from both systemic and spot improvements, and compare 

curves with similar characteristics to help prioritize projects. 
TENNESSEE’S HORIZONTAL CURVE DATABASE

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INTRODUCTION

The Tennessee Department of Transportation (TDOT) has spent almost two decades 

collecting data on their roadway network in an effort to have a complete inventory. In 2012, 

TDOT accomplished this task and completed the initial data collection for its entire roadway 

network, which includes all interstates, state highways, arterials, collectors, and local roads. 

While driving along the roadway network to collect center line data for their Linear 

Referencing System (LRS), on-board software recorded each horizontal curve on the system. 

TDOT compiled and stored the data in a horizontal curve database that is housed in the 

Tennessee Roadway Information Management System (TRIMS)—a client-server application that 

allows TDOT to capture, maintain, and view critical roadway data. The purpose of this case 

study is to describe the challenges and successes in developing and using the horizontal curve 

database in Tennessee. 

BACKGROUND

TDOT used a vendor to collect roadway center line data in the late 1990s using a Global 

Positioning System (GPS) device. The vendor developed software that converted the GPS 

coordinates to horizontal alignment data. The software identified curves with a degree of 

curvature greater than two degrees. TDOT has conducted numerous update cycles using 

internal staff since the initial collection in 2012, and the entire roadway network is now stored 

in TRIMS.

OBJECTIVE

Tennessee strives to use the horizontal curve database to:

• Provide a high level of detail for all curves on the roadway network.

• Identify horizontal curves that have potential for safety improvement.

• Select and prioritize projects with more efficiency and, therefore, better allocate funds.

• Support before-after analysis to quantify the safety benefit once projects are completed.

AUDIENCE

This case study may be of interest to the following audiences: 

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

Geographic Information System (GIS), and Asset Management Units.
TENNESSEE’S HORIZONTAL CURVE DATABASE

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

Departments, Metropolitan Planning Organizations, and Regional Planning Commissions.

• Local Technical Assistance Programs.

• Consultants and private industries involved in safety. 

THE HORIZONTAL CURVE DATABASE 

The horizontal curve data for both local and State roads are stored within TRIMS. TDOT 

originally developed TRIMS in the 1970s. In the late 1990s, TDOT hired a vendor to convert it 

to an Oracle database, resulting in a complete replacement of the legacy system. At that time, 

TDOT converted to a GIS for location coding. TDOT is comfortable with the accuracy of the 

LRS center line data, which was used to derive the curve data. TRIMS provides users with a 

view of roadway data, traffic, bridges, crashes, railroad grade crossings, pavement conditions 

and photolog digital images. The photolog images are digital roadway photographs taken of all 

interstates and state routes. 

Of the 96,000 miles of roadway inventory data in TRIMS, segments accounting for 40,000 miles 

include a curve with greater than two degrees of curvature. The raw data for horizontal curves 

come in as separate database tables and are then imported into TRIMS. The main attributes 

stored in the curve database are the beginning mile point of the curve, the ending mile point of 

the curve, the degree of curvature, and whether it curves to the right or left. There are 

multiple databases in TRIMS that can be linked to curve data. For example, there is a crash 

table, roadway geometrics table (number of lanes, access control, land use, terrain), 

maintenance features table (inventory of signs), roadway description table (shoulder type, 

pavement type, pavement width), and traffic table (average annual daily traffic [AADT], truck 

percentages). 

Any authorized user in TDOT can access the horizontal curve database at any time and for any 

purpose. Parties accessing the database go through the client server TRIMS or through the ETRIMS web application. Local agencies, including municipalities and Rural Planning Organizations 

(RPOs), also have access to the database.

Since the completion of data collection in 2012, TDOT estimates that five percent of the curve 

data need to be updated based on changes in the roadway since 2013. Therefore, TDOT 

updates their roadway inventory on a weekly basis, based on recent changes of roadway items 

through construction progress reports and notifications of local officials. As TDOT receives 

these new updates, an import process updates the data in TRIMS. TDOT is in the process of 

working with local officials to automatically receive notifications when new local roads are 

added. TDOT does not usually realign curves for safety projects, but rather implements other 

low-cost countermeasures—such as signing and pavement markings—because of the high cost 
TENNESSEE’S HORIZONTAL CURVE DATABASE

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and many other projects vying for funding. After these low-cost countermeasures are installed, 

TDOT monitors the sites for crash reductions and can then quantify the safety effectiveness of 

the treatment.

APPLICATIONS OF THE HORIZONTAL CURVE DATA

The Project Safety Office within the Strategic Transportation Investments Division used the 

horizontal curve database to look for locations with four or more crashes with any degree of 

curvature to create the High Friction Surface Initiative. TDOT gathered the data for these 

locations to look at the superelevation and curvature of these sites, and then conducted

meetings to review these sites for potential safety improvements. These meetings vary 

depending on the project, but involve necessary personnel (such as the Long Range Planning 

Division’s E-TRIMS group, the Project Safety Office) when developing safety initiative concepts. 

The Project Safety Office also invites local agencies, RPOs/Metropolitan Planning Organizations 

(MPOs), and district personnel to attend meetings for any safety related projects. Once a 

project is approved, TDOT conducts site visits that involve members of the Traffic Engineering 

Office, Design Division, and Construction Division.

At the end of 2013, TDOT began using the horizontal curve database to locate sites where 

High Friction Surface Treatment (HFST) could be applied to reduce crashes. HFST is the 

application of small, durable aggregates to the existing surface using a polymer binder to restore 

and maintain the pavement friction. TDOT overlaid the curve data with crash data to create a 

statewide map of locations where both wet and dry lane departure crashes occurred on curves. 

TDOT does not monitor pavement friction at horizontal curves on a regular basis because of 

the lack of time, staff, and funds. The Project Safety Office reviewed the degree of curve, speed, 

and slope to determine sites that could most benefit from HFST. To date, TDOT has chosen 

approximately 40 sites to apply HFST. The locations were limited to state routes, but TDOT 

plans to expand the map to include local roads, pending funding availability and local interest. 

At TDOT, every safety project includes an evaluation plan—meaning that TDOT identifies what 

data are needed in order to conduct an evaluation. TDOT participated in peer exchanges with 

other States and received feedback that many States would be interested in Tennessee’s safety 

evaluation of HFST. They conferred with the Federal Highway Administration (FHWA) to 

determine how to develop Crash Modification Factors (CMFs) for HFST. In order to complete 

the analysis, TDOT is accumulating several years of post-treatment crash data. TDOT will 

develop multiple CMFs for HFST specific to different scenarios including wet and dry pavement 

conditions, varying degrees of superelevation, and for all crashes and separately for lane 

departure crashes. 
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RESULTS

It is still too soon to see crash reductions resulting from projects chosen using the database. 

The evaluations will begin once there are enough post-treatment data. However, TDOT has 

already seen significant cost savings because of the horizontal curve database. For example, 

contractors hired by TDOT are able to use the database and do not have to collect new data 

for their own projects. TDOT has also noticed cost reductions on contracts.

The horizontal curve database has utility in a variety of safety analyses. Besides identifying 

potential HFST implementations, TDOT is planning other improvements using the horizontal 

curve database. For example, there are a large number of rural two-lane roads without 

shoulders in Tennessee. Without shoulders, there may not be sufficient spacing for a vehicle to 

stay in the travel lane, even with a wide lane through a horizontal curve. TDOT has identified 

curve locations without shoulders and is evaluating the potential safety benefits from shoulder 

widening. TDOT is also looking at adding lane markings and rumble strips to improve safety at 

curves. 

The horizontal curve database also results in better customer service. Nearly every day, TDOT 

receives queries from the public, press, or elected representatives concerning the safety of 

specific curves. Using the database, TDOT can supply the data to the concerned parties 

instantly. TDOT can immediately identify the degree of curvature, the speed limit, and if there 

are crashes associated with the geometry of the roadway from TRIMS. These data help TDOT 

answer queries in a fast and efficient manner.

TDOT does not use the horizontal curve database to choose projects for local agencies, but 

TDOT conducts a great deal of training for local agencies on how to use TRIMS. However, 

TDOT does share network screening results with local agencies; then, if the local agency is 

interested, TDOT helps them develop the project and, if needed, works alongside them 

throughout the project.

FUNDING

The effort to collect center line data in the 1990s was strictly for state routes, but TDOT 

eventually added the collection of arterials and collectors. This effort was funded through 

TDOT’s ongoing maintenance contract with its vendor. Then, through a Request for Proposal 

(RFP) process, TDOT added data collection of the local roads over a five-year period, which 

was funded through regular State Planning and Research (SP&R) funds. Because the horizontal 

curve data were derived from the center line data and not its own independent project, it is 

difficult to estimate the total cost of generating the horizontal curve database.
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Since the statewide data collection effort ended in 2012, TDOT has continued the database 

maintenance in-house using regular state funds in the GIS Mapping and Facilities Data Office of 

the Long Range Planning Division.

BENEFITS 

TDOT identified the following benefits of a horizontal curve database: 

• Providing quick data-derived answers to public concerns at problem locations to determine 

if locations warrant safety improvements.

• Using the database to make data-driven decisions leads to better use of TDOT funds.

• Quantifying potential benefits from both systemic and spot improvements. 

• Comparing curves with similar characteristics to help prioritize projects. 

BARRIERS AND HOW THEY WERE OVERCOME

TDOT underwent a major update to migrate to a Microsoft Windows 7 platform because the 

previous versions were on an older version of Visual Basic that would no longer be supported. 

TDOT hired a contractor to help with the migration. Since that effort, TDOT is solely 

responsible to conduct the data updates. Although TDOT is short several staff, most updates 

to the roadway inventory do not include changes in the alignment, the horizontal curve data do 

not fall out of date too rapidly and TDOT is generally able to keep up. If someone requests 

data in an area where an update has been done to roadway inventory, TDOT can process 

individual segment updates and produce the data needed, which, would then be added to the 

database.

LESSONS LEARNED

TDOT noted that a valuable aspect of developing a horizontal curve database is to ensure it is 

capable of linking with other databases. For example, a user is able to gather the posted speed 

limit and advisory speed from a certain curve then overlay data from the crash database 

showing crash types and severity. This allows TDOT to identify correlation between curve 

characteristics and overrepresented crash types (such as road departure crashes) at that 

location and to select appropriate countermeasures. It also allows TDOT to compare curves to 

one another to determine which have the most potential for safety improvements.

NEXT STEPS

TDOT plans to develop CMFs for HFST on curves once enough post-treatment data have been 

collected. 
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TDOT is considering the development of calibrated Safety Performance Functions (SPFs). They 

have adopted the Highway Safety Manual (HSM), but development is in the beginning stages at 

this point. TDOT is contacting other States to learn about the process of developing statespecific SPFs and expects another year before making a decision on what to pursue with 

respect to calibrated SPFs. TDOT is also in the process of developing a new Level of Service 

(LOS) database, which will then be linked to TRIMS.

TDOT is constantly seeking new ideas that will improve the safety and operations of the 

roadway network. From that desire to identify new ideas, TDOT observes what other States 

are doing, participates in peer exchanges, and looks for new material (e.g., reports, guidance, 

evaluations) published by FHWA and others. 

AGENCY CHARACTERISTICS

ORGANIZATIONAL STRUCTURE

The Long Range Planning Division of TDOT supplies and maintains the data in the GIS. All areas 

within TDOT can access the horizontal curve database whenever and for any purpose. Parties 

accessing the database go through the client server TRIMS or through the E-TRIMS web 

application. Local agencies, such as municipalities and RPOs also have access to the database. 

PERSONNEL 

The Long Range Planning Division – GIS Mapping and Facilities Office are responsible for the 

maintenance of the databases. Specifically, the GIS, City and County Mapping and Roadway 

Inventory Data Collection Section are responsible for GIS and GPS highway maintenance and 

roadway inventory data collection. The GIS Facilities Data (TRIMS) Section is responsible for 

TRIMS data maintenance, TRIMS application development, and the photolog images. 
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REFERENCES 

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

1) John Hicks and Brian Hurst. Telephone Interview. March 13, 2015

2) Tennessee Department of Transportation website: http://www.tdot.state.tn.us/. Last 

accessed May 8, 2015.

AGENCY CONTACT INFORMATION

John Hicks

GIS Technician Manager I

Long Range Planning Division - GIS Mapping and Facilities Data Office

Tennessee Department of Transportation

505 Deadrick Street

Nashville, TN 37243

John.H.Hicks@tn.gov

615.741.0953 

Jeff Murphy

Transportation Manager I

Strategic Transportation Investments Division, Project Safety Office, Safety Data Division

Tennessee Department of Transportation

505 Deadrick Street

Nashville, TN 37243 

Jeff.Murphy@tn.gov

615.741.0968