Many communities have examples of roadways or intersections that were designed in accordance with standards, but appear to have been over-designed or over-sized compared to the actual motor vehicle traffic needs. According to city engineers and other transportation professionals over-design is not uncommon, and research is needed to determine in retrospect the causes of over-sizing. These roads may have 4-lane sections
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Many communities have examples of roadways or intersections that were designed in accordance with standards, but appear to have been over-designed or over-sized compared to the actual motor vehicle traffic needs. According to city engineers and other transportation professionals over-design is not uncommon, and research is needed to determine in retrospect the causes of over-sizing. These roads may have 4-lane sections where 2 lanes would be adequate, leading to speeding and resultant safety issues, or double left-turn lanes and other features that lead to very wide intersections, which are unnecessary and make crossing difficult for pedestrians and bicyclists. The unneeded pavement cost a lot of money to build, and has ongoing maintenance and future replacement costs.
Roadway over-design – Ask for examples from various local agencies; each jurisdiction could be asked to nominate one or two case study locations. The research would document roadway design and current operational characteristics, and explore the historical design files to determine the design assumptions and design standards. The objective is to determine the causes of over-design for each case study and to indicate opportunities for implementing changes to design standards, basis-of-design LOS, and design procedures that do a better job of balancing peak-hour motor vehicle use versus quality of life for the other 23 hours of the day. Are these the right metrics for decision-making? Examples of design assumption factors to evaluate include the following:
• Peak hour factor
• State aid standards
• Land use changes or land use development forecasts
• Type of vehicle
• Transportation system revisions
• Forecasting (20-year traffic forecasts)
• Basis-of-design LOS in the design year
• Funding rules, or beliefs about funding rules widely held among city/county staff
• Tort liability as design driver (or fears/beliefs about potential tort liability)
Potential Benefits:
More appropriately designed roadways and design flexibility. Significant cost savings from not over-sizing roadways and intersections.
Research will be applied/implemented:
Improve design standards/factors to allow more flexible design to address quality of life. The most likely changes could be in State Aid Rules about number of lanes required, modified methods or application for design-year traffic forecasts, and better decisions for balancing peak-hour accommodation compared to broader measures of community quality of life, but the research should include thorough evaluation of the implementation question.
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