Talking Michigan Transportation

Study: Flashing LED lights can reduce crashes on curves

• Season 7 • Episode 248

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On this week’s edition of the Talking Michigan Transportation podcast, a conversation about a new study that confirms that flashing LED lights, used strategically, can improve safety on curves.

The study is part of a larger project looking for effective speed warning technologies, said Timothy Gates, a professor of civil and environmental engineering at Michigan State University, who talked about the findings on the podcast. 

The research is funded by the Michigan Department of Transportation (MDOT).

The state tallied 128,517 crashes on curved roadways during winter weather conditions between 2018 and 2022, causing 175 serious injuries and fatalities, plus 1,360 less serious and suspected injuries, the study said. 

The study concluded that curves on flat roads (called horizontal curves by highway engineers) "present a major challenge to drivers, especially when there is a significant difference between the posted speed limit and the curve advisory speed."

SPEAKER_01:

Hello, and welcome to the Talking Michigan Transportation Podcast. I'm Jeff Cranson. This week I spoke with Dr. Timothy Gates at the Michigan State University College of Engineering about a recent study he and his colleagues completed on skid season, so-called in some media reports about it. Basically, this study looked at whether flashing LED lights can make a difference in driver behavior on curves. Obviously, anybody who drives knows that there are more crashes on curves, especially in the wintertime when slippery conditions might be present. But this study really looked at what kinds of things will help drivers slow down and be better prepared to drive safely through the curves. A stunning number of crashes occurred on curb roadways during the winter weather conditions between 2018 and 2022. The state tallied more than 128,000 crashes in that time period. At least 175 of those were serious injuries and fatalities. So Dr. Gates talks about what went into the study, uh what the findings helped prove, and what they'll be looking at in the future. I hope you enjoy the conversation. As promised, I'm back with Dr. Timothy Gates, who is a professor in the civil engineering program at Michigan State University. He's been on the podcast before to talk about various studies. He's uh all about finding ways to make transportation safer, which is paramount obviously for anybody involved in the Department of Transportation. Um Dr. Gates, thanks again for coming on the podcast. Well, you're very welcome, Jeff, and thank you for the invitation. So as I mentioned in the introduction, what caught my eye this time was a study from Dr. Gates and his colleagues in Michigan State on how flashing LED lights can make a difference in how drivers approach curves. Uh on the surface, this kind of sounds like one of those uh obvious things that we should all know. Um, like no kidding. But we need studies to oftentimes to validate the things that we think we know, and sometimes they don't, and we get surprises. So to talk about that, I guess, first of all, um the findings, what led to the study in the first place, and if anything out of that surprised you.

SPEAKER_02:

Yeah, well, thanks, Jeff. Um, really good question. And, you know, as a transportation person, you know, we always hear that the the flashing light is one of the last uh last longest standing and last types of driver alert mechanisms that we have that still remains effective. Um, and those flashing lights are effective, but they're even more effective if they're activated in an on-demand situation, like either due to you know a driver uh approaching at too fast of a speed, uh, or uh like a weather sensor, so uh a pavement sensor uh or a weather sensor that senses when the the the weather and uh the pavement surface is uh potentially going to be slippery and it activates that sign. So when we have this the combination of the flashing light and it have it activated in an on-demand sense, so only when needed and not flashing all the time 24-7, um, then that's really still perceived as one of the high the best driver alert mechanisms that we have out there. And so this started with so when we we talk about combining the the flashing signs or the flashing lights, um, there's a few different ways we can portray that to motorists. You can either have the flashing beacon on top of the sign, uh which is the most common, but more recently in the last 20 years, they've actually embedded LED lights in the border of the sign. And you've probably seen those around. They're oftentimes used in airports or um, you know, maybe at pedestrian crosswalks, sometimes even you know, for warning signs, but the much less less frequently for warning signs. But so there's two different types of um um common types of uh flashing lights that are uh integrated within the sign. We we started with the flashing uh sign. Um we started a series of projects about um eight or nine years ago uh for the Michigan DOT, where we were looking at uh different technologies, um different warning technologies. And that really started with the speed feedback signs that you see, the radar your speed signs that gives you the you know when you're approaching the sign. We see them in like, you know, around school zones, municipalities, and even some curves and exit ramps in Michigan. And that's where we started with MDOT, was looking at those uh speed feedback signs that would come on when a driver's traveling too fast for the curve. Um, we started that project, I believe, in 2017, uh looking strictly just at uh speed feedback signs at ramp curves. And then out of that spun a bunch of um follow-up projects, one of which was looking at um using evaluating MDOT's current um bridge deck warning systems, which were again uh a like bridge maybe icy sign that had uh the LEDs and the borders that would only activate when the pavement sensor, the environmental sensor would sense that the pavement was um below a certain friction number. And we found so we did a pretty extensive winter evaluation in I believe it was 2021 and 2022 for MDOT and found that those signs were very effective. Um, but there were issues with the brightness of the LED light. So, for example, a lot a lot of times the bridges when they ice um over, like with black ice and you can't see it, that's you oftentimes in the morning time, um, when you know that's just been a little bit of condensation and freezing overnight on the bridge deck. Um, maybe when the sun's coming up and it's you know, so we had some issues with the uh the um the brightness of those uh lights, but overall uh they were still fairly effective at reducing speeds uh approaching that bridge deck. That then prompted uh the project that we're going to talk about today, which is looking at the use of um or evaluating m dot's use of what we call a slippery curve warning sign. I mean, it's not really that technical, but basically what it is is this uh uh slippery one wet sign, which we probably have uh have familiarity with that has the LED borders and is activated by a pavement sensor that detects when the friction at the surface of the pavement is below a certain value. And so we just wrapped that particular project up. It was evaluating two, uh well, MDOT at the time has only had two of such systems implemented. One was on M32 west of Gaylord, which was the focus of our study. And then there was another one on I-75 nearby, just a little bit north of Gaylord, towards Vanderbilt and Wolverine, um, that also had uh a flashing um you know, series of flashing chevrons. Um, we did not evaluate that one because there was uh, I believe it was out of service during our evaluation. So we just strictly looked at this one system um west of Gaylord.

SPEAKER_01:

And that's that's kind of how we got to where we we are. So that's a heavily traveled stretch of two-lane road in the wintertime. I can see it. It is um everybody that comes up from Southeast Michigan, Metro Detroit, to either snowmobile or make their way to Boyne Mountain uh gets off at 75. That's exactly right. Yep.

SPEAKER_02:

And so and there's a series of curves through there that are uh quite sharp. Um and we all know, especially you've seen it in the news the last couple of years, Gaylord has seemed to have uh been kind of the epicenter for severe weather, um, both, you know, with last year and this year getting nearly two feet of snow over Thanksgiving and then ending this the winter season in March, April, whenever it was that they had the uh ice, the very significant ice storm. Um, so yeah, they do get a lot of it, you know, and let's face it too, like, you know, plows can't be everywhere at all times. Um, and so if you have these these locations that are maybe a little bit uh of a distance from a plowyard or that are maybe not as high priority as say uh I-75, where you'd have your workers on I-75 plowing as uh and de-icing as much as possible. So certain areas we need other things to help. You know, if we're not able to get out there and clear the snow and ice as quickly as we can, you know, maybe have another treatment that will alert motorists. Now, again, it gets back to the fact that you really only want to turn that alert on when it's needed, right? So determining when it's needed is a big because otherwise drivers will disregard it if it comes on and it's not slippery and it's all you know, it's like the crying wolf type thing. And then suddenly there actually is the wolf. The there is a pretty you know significant amount of black ice out there, and you end up running off the road and you know colliding with whatever.

SPEAKER_01:

So, anyways, that yeah, that's that's where we're at with so it's it's it's one more way to I mean, this is why I know traffic safety engineers, and I think people who teach in colleges of engineering and talk about safety don't like it when somebody says that road is dangerous or that curve is dangerous or that intersection is dangerous. It's only dangerous if uh you don't drive appropriately for conditions, right? Well, that's very true. Yep, yep. And so what we're trying to do, what you're trying to do with these devices and techniques is help people be better drivers. Right.

SPEAKER_02:

That's exactly right. And um there were actually two components. There were several components to the most recent project that we did for MDOT, which was looking at speed warning technologies in in rural areas. And you know, we looked at a variety of horizontal curve warning strategies. We looked at like, you know, a new uh several implementations of speed feedback signs on exit ramps along I-94, which were implemented uh based on the recommendations of our prior study that wrapped up in 2020 or 2021. We looked at the use of uh feedback signs on freeway mainline curves. There are, I to my knowledge, were none that existed. So we did some temporary installations on freeway mainline curves around Mount Pleasant on US 127. And then uh we also mdot had recently implemented a flashing chevron uh system, warning system based on drivers approaching at too high of a speed. Uh several curves in the Irish Hills along US 12, um, like the done by I think it was like Napoleon or Brooklyn area. Um there was uh four such curves that were implemented through there. Um I'm sorry, three curves that two curves and they were directional, uh eastbound and westbound systems. Explain chevrons for the unit. Yeah, so so similar to like a uh uh the speed feedback sign, so the chevrons is as you go through the curve, you see the the black and yellow, um, you know, kind of just like an arrow, but it's a truncated arrow. So this is a chevrons showing you the path uh through the curve that you need to follow. And these were um uh for lack of a better term, kind of uh you know, uh sneaky type curves where you couldn't necessarily see just how significant uh the curvature was. And so MDOT, this is in the university region, had uh had uh a contract to install these new flashing um Chevron systems. Now, they again, like I said before, they don't flash at all times, right? Because they would get disregarded if they flash at all times. But there was a uh radar sensor that was positioned a little bit in advance of the curve that would detect if a motor was traveling too fast for the curve, um, and then would start to flash them, you know, if if it was detected that they were traveling above that threshold speed in hopes that they would reduce their speed and you know travel safely through the curve. Now, one thing we did test on that, because there's not that there's not a lot of um specific guidance at the federal level and the M U T C D, the manual of uniform traffic control devices, is we actually tested the simultaneous flash, so all of them flash at the same time versus the chasing, the sequential chasing flash where one uh only one flashes at a time and they flash in a sequence. So it's like you know, showing you the path through the curve in sequence. And we found that there really wasn't a lot of uh they they both both of them had speed reduction uh effects. Um, there wasn't necessarily a clear trend of which one was better, which one was worse. Um, you know, and and so these are the types of things research-wise, we can take those to the I also sit on the National Committee of uh for uniform traffic control devices that provides information um to the uh the federal highway administration about the MUTCD. I have shared uh a lot of this research, these research results with that committee um to help um better inform future versions of the MUTCD. Uh so yeah, so that's the flashing chevron.

SPEAKER_01:

Those peer reviews are are very important, and I think uh peer exchanges. Stay with us. We'll have more on the other side of this important message.

SPEAKER_00:

Michigan log requires drivers to maintain at least 200 feet behind a snowplow when crews are plowing or treating roads and have their lights on. This does not apply when passing the snowplow. In addition, stay at least 20 feet away when the plow is stopped or at an intersection. Failure to do so can result in a fine of$100. The log is meant to ensure snowplow operators have the proper space and time to clear the roads. This makes Michigan's roads and neighborhoods safer to drive on and walk around throughout the winter. Always remember, snowplows need room to groom.

SPEAKER_01:

So I think that the statistic that jumped out at me most from the reporting on this was that 128,000, more than 128,000 crashes are on curved roadways during winter weather conditions. That was just between 2018 and 2022. Now, instinctively I would have said certainly there are more crashes on curved segments of roadways than than straightaways. But that that number is astonishing. I mean, were you even surprised at the volume?

SPEAKER_02:

Yeah, it it's quite surprising. And I mean, a lot of these are property damage, they slide off and you know, they whatever, slide off and collide with the embankment or, you know, tree at low speeds or something like that. But, you know, we really try to to limit these things. There's obvious reasons why curve crashes occur, right? You've got a bend in the road, and if a driver's not paying attention or traveling too fast, they, you know, potentially slide off to the outside of the curve. Um, and so obviously those problems are magnified when the the surface friction is even lower, uh, and magnified further if the visibility is bad. Like if you've got an active snowfall event and you know, if the driver's not familiar with that roadway, then it really becomes a problem. So these on-demand flashing systems are really important, um, and especially so for uh winter weather warning um uh at these curves where uh regular snow and ice is a problem.

SPEAKER_01:

And do you think um because you talk to people in other states about this, um, and because you know Michigan has had like like some states, some states are doing very well, some are struggling with funding and have been for decades, like Michigan. We know things now that we didn't know 50, 60 years ago when these roads were designed and built. And um, if it was about buying right-of-way or the the difficulty and and just you know designing a straighter road, we really don't have the money to redesign all these roads now, so you're gonna have to. I mean, there's gonna be big business for figuring out how to make these curves safer for a long time, right?

SPEAKER_02:

Yeah, that's correct. Um these are these systems are are obviously much cheaper than realigning a road, right? We know we I think we understand that there's a there's a handful of things that we can do as engineers. Um, and and usually any good engineer has wants to, you know, make sure that they're very aware of the costs of these things and trying to implement cost-effective treatments because we can put more of them out there if they're cheaper, right? And we put them in more locations than say, uh, you know, spending uh the the time and expense it cost uh to realign the roadway, straighten things out. Of course, we'd like to have everything straight and flat, right? But you know, we know that's not practical due to natural terrain and you know, bodies of water and property value, properties and property values, et cetera, et cetera. Um, so yeah, so that's why we have curves out there. Um, they are important part, they're never going to go away completely. Um, but uh yeah, so we need to come up with more low-cost um traffic control solutions to help guide motorists in these situations.

SPEAKER_01:

So talk about what's next. What what's uh what's in your your current uh portfolio, I guess, and and what you'll be looking into um in the future.

SPEAKER_02:

Sure. So um just to kind of tie things up here with the the winter weather treatments, every single winter weather treatment we we have looked at, including the the slippery curve warning system uh with the flashing LED sign borders. I mean, that those are um we we recommended that MDOT and other agencies continue to implement them, expand so expand the use uh of those systems, um, especially in areas that are prone to frequent severe weather conditions, and even more so areas where you know maybe they're a little bit of a ways or not high priority on the the plowing uh the plowing list uh or de-icing list. Um, in terms of where we're going next, so that project wrapped up this past year. That's why you're starting to see some of the publications um um hit. Uh the next project, and it's starting very soon. Um, I don't know if we have a specific start date yet, but we were awarded it. Um, is a project looking at um speed warning treatments for uh communities. So largely transitioning from the high-speed rural highway into let's say a small town or you know a rural community um where there might be a crosswalk or a you know a small downtown area or school. So, you know, these areas where drivers are basically getting drivers' attention that they need to slow down as they're approaching this small town. And we're not talking about like somebody coming into a major city like Detroit or or Lansing, where it's clearly obvious that the land use is changing and you've got pedestrians and the, but it's more these, you know, the rural highways uh along you know the the state trunk lines coming into a rural community. But speed transitioning, yep, cities and villages, yes. Yep, yeah. And and you know, it just I shouldn't say only state trunk lines, and obviously county roads do come into communities as well, but you know, because this is an MDOT project and m dot has plenty of such uh uh scenarios out there where you've got the trunk line coming into a small town um in a rural area, uh that that's largely where we're going to focus. Um, and we're not going to just focus in that speed transition area. We want to see what the impact is at the crosswalk, for example. You know, our drivers maintaining that low speed when they reach the crosswalk or reach the school zone or whatever it may be.

SPEAKER_01:

Yeah, that's that'll be interesting to watch too. Obviously, we can't do enough to uh to emphasize the importance of that safe driving in open schools. So thank you as always. Uh, it'd be interesting to watch how this next one unfolds, and I appreciate you explaining this, and I really appreciate the work that you do to try to make our roads safer, and we'll have to talk again sometime.

SPEAKER_02:

Well, you're welcome, Jeff. And again, thanks for the opportunity, and thanks for doing what you do, which is spreading the word about uh safety treatments throughout the state of Michigan and beyond.

SPEAKER_01:

You can find show notes and more on Apple Podcasts or BuzzSprout. I also want to acknowledge the talented people who help make this a reality each week, starting with Randy Debler, who skillfully edits the audio, Jesse Ball, who proofs the content, Courtney Bates, who posts the podcast to various platforms, and Jackie Salinas, who transcribes the audio to make it accessible to all.