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Put Your Roads on a Diet to Improve Traffic Safety
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In the early days of motor vehicle travel, an urban area’s transportation infrastructure consisted mostly of two-lane roads. This provided sufficient traffic flow for the relatively small number of vehicles. But over the years, vehicle ownership rates rose and traffic congestion increased. Our roads needed to be updated to support this increasing traffic.
In the 1950s and 1960s, the problem of higher traffic volume was solved by increasing the number of lanes on the roads, from two to four. There were no engineering groups exploring other options or considering whether four-lane roads were the best solution in all cases.¹ Four-lane roads became the norm for urban areas throughout the country.
As a result, our roads got bloated.
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In the years since, we’ve gained a better understanding of the challenges that four-lane roads present to road safety, including:
- Rear-end crashes involving speeding vehicles or vehicles turning left
- Sideswipe crashes as vehicles frequently or suddenly change lanes
- Crashes as side street traffic attempts to cross four lanes
- Bicycle crashes caused by insufficient road space
- Pedestrian accidents as pedestrians attempt to cross four lanes of traffic
To counteract the dangers posed by four-lane roads, the Federal Highway Administration (FHWA) is now recommending that we put our roads on a diet.
What Is a Road Diet?
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The term “road diet” generally means removing lanes from a road and using that space for other purposes. Typically, this road rechannelization involves turning an undivided four-lane road into a three-lane road with two through lanes and a center two-way left-turn lane.² The safety benefits of this relatively easy, cost-effective countermeasure can be significant. In fact, studies suggest that a road diet converting a road from four lanes to three can reduce total crashes 19-47%³ and can reduce crashes involving both drivers under 35 years old and those over 65 years old.⁴
Here are just a few of the safety benefits of a lane reduction from four lanes to three:
- Reduced rear-end and left-turn crashes because of the dedicated left-turn lane
- Reduced number of lanes that side street traffic and pedestrians need to cross
- Calmed traffic traveling at more consistent speeds
- Increased space for bicycle lanes, pedestrian refuge islands, parking or transit stops
Choosing the Right Road Markings to Make Your Road Diet Successful
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To ensure that your road diet is successful, it’s important to choose the right pavement markings to help drivers interpret and react to the road. And in challenging conditions like nighttime or rain, not just any markings will do.
Here are a few key characteristics of effective pavement markings:
- Luminance: In order for drivers to stay in their lanes and navigate the road, they need to be able to see the lane markings. The luminance, or brightness, of pavement markings is a critical factor when it comes to ensuring that drivers can consistently see the markings.
- Contrast: No matter how bright a pavement marking is, it will be undetectable without sufficient contrast between the marking and its background (either the road or a contrast stripe next to the pavement marking).
- Retroreflectivity: Retroreflective materials are designed to return light from a vehicle’s headlights back to the driver, making pavement markings visible to drivers at night.
- Wet Retroreflectivity: Standard pavement markings use retroreflective optics with a refractive index (RI) of 1.5 — engineered for visibility in optimal conditions. However, when it’s raining or the roads are wet, the pavement marking’s optics can become surrounded by water. As a result, light reflecting off of the optic is spread out in a much broader, weaker cone. This means that less light from a driver’s headlights will be reflected back to the driver, making the pavement marking very difficult to see. New wet retroreflective pavement marking technology uses ultra-high 2.4 RI optics to reflect a narrower, more focused cone of light and counteract the impact of water to make your pavement markings visible in wet and rainy road conditions.
- Durability and Consistency: Pavement markings on real-world roads undergo a great deal of adverse conditions and wear and tear. To help ensure that drivers can continue to see the markings over time, it’s critical that the pavement markings are durable enough to maintain their luminance, contrast and retroreflectivity.
- Visibility for Automotive Cameras: It’s also important to plan for vehicles equipped with advanced driver assistance systems (ADAS) like lane departure warning (LDW) and lane keep assist (LKA). According to SBD Automotive, “In the U.S. market, 60% of vehicle models sold from MY2016-MY2017 offered lane departure warning systems as a standard or optional safety feature,”⁵ and the Highway Loss Data Institute estimated that by 2025, over 40% of all registered vehicles will be equipped with standard or optional LDW.⁶ These ADAS-equipped vehicles use cameras to help keep a vehicle on the road and in its lane. Pavement markings with improved visibility and increased wet retroreflectivity help these systems more confidently detect lanes in a range of conditions. This, in turn, helps the system keep the vehicle in its lane.
- Luminance: In order for drivers to stay in their lanes and navigate the road, they need to be able to see the lane markings. The luminance, or brightness, of pavement markings is a critical factor when it comes to ensuring that drivers can consistently see the markings.
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References
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¹ https://safety.fhwa.dot.gov/road_diets/guidance/info_guide/ch1.cfm#s12
² https://safety.fhwa.dot.gov/provencountermeasures/road_diets/
³ https://safety.fhwa.dot.gov/provencountermeasures/road_diets/
⁴ Source: Stout, Thomas B., Before and After Study of Some Impacts of 4-Lane to 3-Lane Roadway Conversions. March 2005.
⁵ Source: SBD Automotive — ADAS Tracker — AUT 534. June 2016.
⁶ Source: Predicted availability and fitment of safety features on registered vehicles. (2017). Institute, Highway Loss Data. Vol. 34. No 28, September 2017.
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Interested in learning more?
Get information about road markings that are easy to apply, provide all-weather visibility and will help you plan and execute a successful road diet?
Check out our 3M Pavement Markings
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