6.4 Safety Analysis Applications

6.4.1 Interstate Access Justification Report (IAJR)

IAJR involves an evaluation of a change in access along Interstates. One of the evaluation criteria is safety. The safety analysis may conclude that the proposed change in access does not have a significant adverse impact on the safety of the Interstate facility or on the local street network based on the current and the planned future traffic projections. The scope and methodology for safety analysis is typically based on the project type, location, complexity, crash history, and need and purpose. Safety analysis for IAJRs includes one of the following options:
  • Option A ‐ Historical Crash Analysis and HSM Predictive Method; and
  • Option B ‐ Historical Crash Analysis and evaluation of CMFs
Option A is the preferred methodology. If the HSM predictive method cannot be used, option B may be allowed as per the IAJR methodology, assumptions, coordination, and project scoping.
The safety analysis study area for an IAJR is suggested to be the area impacted by the proposed project. The traffic analysis study area is a good starting point, but the safety analysis study area depends on the safety impacts of the proposed project and may be more encompassing than the traffic analysis study area. The safety analysis study area along the Interstate includes at least the adjacent interchanges on either side of the proposed access change. Along the crossroad, it extends at least one‐half mile from the ramp terminal and includes the first major intersection.
Historical crash analysis is typically conducted for five complete calendar years (January 1st to Traffic and Safety Analysis Procedures Manual | 2024 6-20 December 31st). The results of the analysis are used to identify or confirm safety issues within the project study area. The analysis includes:
  • Crash frequency by facility type for each year;
  • Crash rates and comparisons with statewide average for similar facilities;
  • Crash severity by facility type for each year;
    • Mainlanes
    • Frontage roads
    • Ramps
  • Crash contributing factors;
  • Manner of collision for each year by time of day; and
  • Crash diagrams such as heat maps, bar charts or other maps graphically showing the high crash locations along the study area roadways or at the interchanges
Predictive Crash Analysis (Predictive, or quantitative safety analysis) involves using HSM based methods that use SPFs and CMFs to estimate the anticipated change in crashes from existing conditions to the proposed design. It is recommended that predictive analysis be performed for no‐build and build conditions for the design year. Typical applications for safety analysis tools are detailed in
Section 6.2
 of this chapter. For additional details on safety analysis for IAJRs, please see TxDOT’s IAJR SOPs and SOPs FAQ in
Appendix G, Section 5 – External References (Reference 7)
. See
Appendix G, Section 8 – IAJR SOP FAQ Webinar Slides
 for additional information about the Standard Operation Procedures.

6.4.2 Design Exceptions

A design exception is necessary whenever the controlling criteria specified for the different categories of construction projects (such as, 4R, 3R, 2R, Special Facilities, Off-System Historically Significant Bridge Projects, OnSystem Park Road Projects, and on-street Bicycle Facilities) are not met. Design exceptions add flexibility to meet project needs (i.e., balancing costs, ROW, environmental considerations, modal access, and performance). A design exception is comprised of multiple comparisons, with the safety analysis being just one part of the process. The request for design exceptions is recommended to include a summary and analysis of the crash history at the location. An explanation is suggested to be provided on how crash history relates to design exceptions and predicted safety performance of the project under development. For the latest guidance on design exceptions, refer to the TxDOT RDM. Safety analysis for design exception requests include the following:
  • Need;
    • Project description
    • Project location map
    • Location of design exceptions
    • Alternatives
  • Description of Anticipated or Proposed Design Exceptions;
  • Area of Influence;
    • Mainlane
    • Crossroads
  • Analysis Years (if applicable);
    • Existing
    • Opening
    • Design
    • Interim
  • Data Collection;
    • Historic crash data
    • Traffic volumes
  • Safety Analysis;
    • Historical crash data analysis for the latest three to five years
    • Predictive/Expected number of crashes (if applicable)
    • Safety analysis of alternatives
  • Analysis Tools; and
    • Predictive Crash Analysis – See
      Section 6.1
       of this chapter for application of predictive crash analysis
  • Safety Analysis of Possible Mitigation/Countermeasures
For more information on design exceptions see TxDOT’s request for a design exception form. The design exception form can be found on
Appendix G, Section 5 – External References (Reference 6)
. As of May 2024, TxDOT has also developed draft Design Exception SOP for Interstate projects, which will be available online later