As part of the NCHRP research studies used to develop the HSM crash prediction models, several spreadsheet tools were developed to assist in the implementation of the HSM Part C predictive method. The HSM Spreadsheets are Microsoft Excel-based tools maintained by AASHTO that were created for the purpose of simplifying the implementation of the HSM Part C predictive method. The following four HSM Spreadsheets related to the various chapters in the HSM have been developed:

The use of the HSM Spreadsheets allows the user to manually enter data and determine the segmentation of the safety study area. The latest version of these tools, along with additional information, is available on AASHTO’s HSM website, which is located in

Appendix G, Section 5 – External References (Reference 3)

.

Several agencies have expanded and modified the HSM Spreadsheets to meet their specific needs. These changes include automation, increased flexibility, and additional features. These modified spreadsheets are not designed for general use in Texas but may be a useful resource for very specific application needs. Several of these modified tools are located on the HSM website. The use of modified spreadsheets can be accepted by the TxDOT Project Manager that will be approving the completed analysis prior to use.

IHSDM is a suite of software analysis tools developed to evaluate the safety and operational effects of geometric design decisions on roadways. IHSDM is meant to be used as a decision-support tool by providing estimates of the expected safety and operational performance of a roadway design. It checks existing or proposed roadway designs against relevant design policy values. The results of the IHSDM support decision-making in the roadway design process. This software is intended to be used by project managers, designers, and traffic safety reviewers in State and local agencies and by engineering consulting firms. As of 2024, the IHSDM software is available for free from the FHWA software overview site, but FHWA no longer supports development of this software. A link to the software is located in

Appendix G, Section 5 – External References (Reference 4)

, and includes the following six evaluation modules:

The crash prediction module was developed to help support the implementation of the HSM Part C and is considered a faithful implementation of the HSM predictive method. The crash prediction models in Chapter 10, Chapter 11, Chapter 12, Chapter 18, and Chapter 19 are included in IHSDM, along with other crash prediction models developed since the publication of the HSM. IHSDM crash prediction modules can be used to do the following

The following facility types can be analyzed with IHSDM:

Data entry and segmentation can be done manually, as in the HSM spreadsheets. The software also has the capability to import alignment files to automate parts of the data entry and segmentation process. Data can also be copied and pasted in from another spreadsheet to increase the usability. Data can be entered either based on milepost or station. Additional information about facility types and data considerations is available in the help feature of the IHSDM software.

ISATe is another HSM Excel-based spreadsheet tool developed by FHWA to help practitioners implement the HSM Part C predictive method for freeways, ramps, interchanges, and collector-distributor (C-D) roads, as identified in Chapter 18 and Chapter 19 of the HSM. ISATe is intended to help agencies make informed decisions related to the safety performance of design alternatives and changes to existing freeway systems. The ISATe spreadsheet and user manual can be downloaded from AASHTO’s HSM website, which is located in

Appendix G, Section 5 – External References (Reference 3)

. Data entry and segmentation for ISATe is very similar to the HSM Spreadsheets.

The SPICE tool is a macro-based, Microsoft Excel spreadsheet that was developed to provide practitioners the ability to evaluate the anticipated safety performance of various control types or intersection types within one tool during the scoping and screening stages of the project development process. This tool was specifically developed to help practitioners performing Intersection Control Evaluations (ICE) to identify alternatives to consider for additional analysis. The SPICE tool can be applied to the following intersection control types:

The SPICE tool is a static tool that does not allow for the flexibility that is available in some of the other crash prediction tools. The purpose of the SPICE tool is to allow the practitioner to evaluate a wide variety of intersection control types and select the most applicable control types that are then further evaluated using one of the more detailed tools like IHSDM or the HSM Spreadsheets. The SPICE tool can be used in conjunction with the CAP-X tool to perform preliminary analysis of intersection control types. Links to download the SPICE tool and user guide can be accessed on AASHTO’s HSM website, which is located in

Appendix G, Section 5 – External References (Reference 3)

, or the CMF Clearinghouse resources website, which is located in

Appendix G, Section 5 – External References (Reference 5)

.

The HSS performs crash prediction evaluations for roadway facilities based on the developed HSM methodologies. Similar to IHSDM, the HSS is another safety software tool developed to implement the HSM predictive method. The HSS software can be used to evaluate the following facility types:

The HSS software is distributed as part of McTrans HCS and comes with a comprehensive user’s guide to provide the needed references for the user along with the data requirements.

The HSM Spreadsheets were developed as part of the NCHRP Project 17-38 to implement the HSM Part C predictive methods for rural twolane two-way roads, rural multilane highways, and urban and suburban arterials.

IHSDM is typically used more frequently by practitioners for analysis of complex or larger projects. Segmentation is automated if LandXML files are available to import. The crash module for the IHSDM includes a "sitebased analysis tool" that can be used without having to include the detailed horizontal and vertical alignment and cross-section data.

ISATe is a spreadsheet-based tool that implements the HSM predictive methods for freeways and ramps. Its application is very similar to the developed HSM Spreadsheets.

The SPICE tool was developed to evaluate the anticipated safety performance of intersection control strategies within a single tool. The SPICE Tool uses the SPFs in Part C of the HSM (and subsequent NCHRP Reports) to select high-quality CMFs from Part D of the HSM and CMF Clearinghouse. The SPICE tool automates many of the decisions necessary for selecting the appropriate SPF or CMF to apply. The SPICE Tool only provides predicted crash frequencies and severities for intersections. The SPICE Tool is not intended to replace the functionality of other tools, including the HSM spreadsheets, ISATe, or IHSDM.

The HSS performs crash prediction evaluations in roadway facilities based on the HSM Part C crash prediction models. SPF and the CMFs are presented for the various facility types. HSS can conduct a standalone evaluation of a segment and intersection or analyze corridors composed of a series of segments and intersections. Each of the crash prediction tools is considered to faithfully implement the HSM Part C crash prediction models. The difference between these various tools is in their approach to allow the user to input the data needed to run the predictive analysis.

FHWA requirements surrounding predictive crash analysis only apply in situations to which the predictive tool can analyze the project.

A summary of the predictive safety analysis tools is shown in

Table 6-5

. This table shows the types and applications of predictive safety tools.

TxDOT has SSTs for two-lane rural roadways, multi-lane rural roadways, and urban intersections. Information regarding these tools can be found in

Appendix G, Section 7 – Safer By Design

. Static versions are also included in

Appendix G, Section 1 – Rural Multi-Lane Road Segment Safety Scoring Tool, Appendix G, Section 2 – Rural Two-Lane Road Segment Safety Scoring Tool, and Appendix G, Section 3 – Urban Intersection Safety Scoring Tool

. TxDOT also has an Eligibility Matrix used as guidance for determining when the SST is applicable to a project. The Eligibility Matrix for the Rural Highways is shown in

Appendix G, Section 5 – External References (Reference 14)

and the Eligibility Matrix for Urban Intersections is shown in

Appendix G, Section 5 – External References (Reference 13)

. The goal of the SSTs is to understand safety effects of design elements and optimize safety before a project is constructed. There is no specific safety score to aim for. The intent is to get the highest score for a particular project, given the constraints. These tools make use of several SPFs and CMFs. The tools can be used for all phases of project development, however, the most value is in using it during the initial scoping stages. Scores from the initial scoping phase and at final PS&E are necessary for reporting purposes. Safety scorings are necessary for PM, 2R, 3R and 4R projects. These project types are defined in TxDOT’s RDM.

HSM models were developed based on the data from States other than Texas. It would be logical to develop new models to address the HSM limitations and calibrate existing HSM models to Texas conditions. TxDOT has completed a couple of research projects which provided local SPFs or calibration factors for all types of facilities. These methods are incorporated into spreadsheet tools to be implemented in the new models. The implementation phase is currently underway which would provide hands-on trainings to TxDOT practitioners. Information regarding local SPFs and calibration factors can be found in

Appendix G, Section 6 – Safety Prediction Models.