Jasmine: Hi, I'm Jasmine.
Chrissy: I'm Chrissy.
Jasmine: We're from NIU STEAM and...
Chrissy: You're listening to The Sound of Science on WNIJ.
Jasmine: Joanna, from Downer's Grove, would like to know: "How is it that speed limits are determined and why they vary from state to state?"
Chrissy: During one of the busiest travel periods of the year, this is a very timely question! Speed limits are typically set by State Departments of Transportation, local county and municipal governments, and federal agencies like the Federal Highway Administration.
Jasmine: When these organizations determine speed limits, they use a combination of factors. Engineering studies are conducted where road geometry, traffic volume and vehicle type, and road conditions are surveyed and considered when determining what speed is safest for the area. Historical crash data is gathered to identify areas with high crash rates, especially when those collisions occur as a result of speed.
Chrissy: If a State, county, or municipality seems to differ from speed limit patterns seen elsewhere, it may be based on a few factors. Methods of data collection may vary from place to place, yielding varying results that may affect where the speed limit is set. Local conditions may also affect speed limits such as steep, hilly grades, narrower traffic lanes, or sharp curves. Policy priorities may also play a role if the area government is looking to promote safety initiatives or affect rates of travel.
Jasmine: Funding, though not always directly linked, may also provide incentive for various government entities to set speed limits at a certain value. The Highway Safety Improvement Program and Transportation Alternative Program provide federal funding to States and is allocated based on crash rates, safety performance, and adherence to federal transportation guidelines. State governments may also prioritize funding or provide incentives to local municipalities that implement safety measures and support guidelines.
Chrissy: You have been listening to The Sound of Science on WNIJ, where you learn something new every day.
