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