When Johnson County, Kan., hired McClure Engineering Company to update their design standards for roads, Howard Lubliner and Cheryl Bornheimer-Kelley saw it as an opportunity to leverage their research in crash prediction models and understanding of road maintenance to improve safety for motorists while positioning the County to invest strategically in their infrastructure and deliver long-term value to its constituents.
When updating the standards, Lubliner’s and Bornheimer’s innovative approach applied their research along with best practices of design consistency, context sensitivity and performance-based design to prepare the County to better serve its motorists for the next 30 years and beyond.
“While studying at the University of Kansas, Cheryl and I performed research to calibrate and validate the Highway Safety Manual’s crash prediction models for rural roads,” said Lubliner, former managing director of infrastructure services. “For this project, we took our academic research and applied it to help the County make strategic improvements to roadway design and safety.”
The foundation of the new design standards is a typical section for each roadway type, based on the current and future use of the roadway. The typical sections were mapped and grouped to ensure route continuity for motorists. Then for each typical section, the team calculated the safety benefit and cost-benefit ratio for various roadway improvements, such as shoulder width and foreslope, based on the Highway Safety Manual and their research.
“By offering the County data on the optimized safety benefit of road investments, we were able to give them valuable tools for improving safety,” said Bornheimer-Kelley, transportation engineer. “Rather than trying to estimate what might make the most sense to spend money on, they now have empirical evidence to support their investments, so they can make roadway improvements with the confidence that they are making the improvements with the most value.”
Another unique aspect of the road standards is the way they account for time and long-term degradation of the roadbed. As a road’s pavement deteriorates, the pavement will be overlaid three to six times prior to reconstruction. The result is a pyramid effect where the road and its shoulder becomes narrower and the foreslope becomes steeper with each overlay.
Not only does the narrowing of the road increase the likelihood of crashes, but the steeper foreslope may increase the severity of crashes, and the reduced ditch capacity can cause stormwater issues.
“Our standards prescribe that the typical sections should be built wider than the optimized width, so the road can easily accommodate future overlays while never becoming sub-standard,” said Lubliner. “By considering the reality of deterioration and maintenance, we were able to help the County develop standards that will maintain their safety benefit throughout the road’s lifespan.”
Additionally, the added width means that during the pavement overlay, there will not be the need for re-grading work to tie in the foreslope of the road. This can add substantial unneeded cost to a road overlay project focused on pavement quality preservation.
For Lubliner and Bornheimer, the project with Johnson County serves as a case study for how their research can improve safety through performance-based roadway design and maintenance standards.
“There are many counties, cities and municipalities throughout the region that are operating with standards that have become outdated,” said Lubliner. “Johnson County, Kansas, serves as a great example of how investing in updating road standards will pay dividends for the community in terms of safety and maintenance costs. By using crash-prediction research and our understanding of roadway maintenance, we can help communities improve the safety and resiliency of their transportation infrastructure.”