Part 3: From Better Signing to Better Safety

For years, agencies have relied on methods that can produce different answers for the same underlying problem. The real weakness in curve advisory speed practice is inconsistency. Computational workflows offer something traditional field methods struggle to provide: repeatability. A system such as SafeCurves does not invent a new rulebook. It operationalises the same technical architecture agencies already recognise.

In practical terms, that means the workflow can evaluate travel path radius, tangent speed, and superelevation using explicit rules rather than ad hoc field judgement, then apply the resulting advisory speed logic systematically in each direction of travel where appropriate. The key point is not automation for its own sake. It is that a standard becomes far more useful once it can be applied the same way everywhere.

This matters because the FHWA handbook was written with exactly this problem in mind. Its purpose was to improve consistency in curve signing and, in turn, improve driver compliance with the advisory speed. In other words, the standards already assume that consistency is a safety issue, not just an administrative preference.

But the bigger opportunity is analytical. Once an advisory speed standard can be applied consistently, it becomes possible to test it properly. The question is no longer just whether an individual plaque is technically correct. The harder question is which standard produces the best safety outcome.

That is why better signing is only the middle chapter. The larger question is what delivers the best safety outcome. By making application consistent, computational methods create the conditions for a much better test of safety performance. And that moves the conversation beyond habit and inherited practice toward something far more useful: an evidence-based advisory speed standard that drivers can trust and agencies can defend.

The epilogue takes that argument one step further: from consistency in application to evidence about which standard works best.

If you’ve reached this part, you will probably find these references enlightening:

• Leaming, E. S. (2014). Curve Evaluations using Rieker’s CARS. Shakedown and development of methodology. Oregon Department of Transportation.
• Bonneson, J, M. Pratt, J. Miles, and P. Carlson. (2007) Development of Guidelines for Establishing Effective Curve Advisory Speeds. Texas Department of Transportation, Texas. FHWA/TX-07/0-5439 1
• Dixon, K., Rohani, J. (2008) Methodologies for estimating advisory curve speeds on Oregon highways. Oregon State University, Oregon. FHWA-OR-RD-08-04
• Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD(2023)), Federal Highways Administration
• Milstead, R., Qin, X., Katz, B., Bonneson, J., Pratt, M., Miles, J., Carlson, P. (2011) Procedures for Setting Advisory Speeds on Curves. Federal Highway Administration. Washington, DC. FHWA-SA-11-22