Spillover Effects ft. Dr. William J. Horrey of the AAA Foundation for Traffic Safety

[00:00:00] Now in the middle of one of the most significant eras in automotive, Carl Anthony amplifies the minds and voices behind this historic transformation as the host of AutoVision News Radio, all while coming to terms with middle age, father loss, and what it means to be successful in Detroit.

[00:00:17] In the summer of 1997, my late father taught me how to drive on my Iowa learner's permit. A college professor by day with a Hewlett-Packard calculator and a gigging musician by night with a Fender Stratocaster, dad would rush home after summer classes in the early afternoon but before band jobs at night to take me out on the roads around Plymouth and Woodbury counties.

[00:00:43] On those main roads like Highway 75, 3 and 20, the speed limit was 55. Dad would recall the time in 1974 when the US government passed the National Maximum Speed Limit Law which established the 55 mile an hour speed limit in response to the 1973 oil embargo.

[00:01:06] My father, a business and economics professor was fascinated by this period in American history when it came to the classroom. At home, dad's focus was the family budget.

[00:01:18] He often said that driving 55 meant better fuel economy for his Chevy Silverado, joking that we could take more practice runs on my learner's permit if we kept it on the double fives.

[00:01:31] In fact, you may even remember how some vehicles back in the day had 55 accented or highlighted on the speedometer.

[00:01:39] Although good for a discussion with students and balancing the checkbook at the kitchen table, my dad's belief in the 55 mile an hour speed limit came in the form of safety.

[00:01:50] To this day when I see a higher speed limit of 75 or 80 miles per hour, it just doesn't register with me and I'm always hesitant to go that fast thanks to my time with my father back in 1997.

[00:02:03] According to research from the AAA Foundation for Traffic Safety, raising the speed limit on a highway or interstate that runs through or is near a smaller town may result in spillover effects.

[00:02:19] Adding to the concern is how local communities are not always involved in the decision making process to raise the posted speed limit on the highway or interstate nearest to them.

[00:02:31] To shed light on this body of research from the AAA Foundation for Traffic Safety and spillover effects is Dr. William J. Horry.

[00:02:40] As the associate editor of the Human Factors Journal and one of the most recognizable voices for the Foundation, Dr. Horry has led or contributed to countless research projects involving driver distraction, driver behavior and safety, human automation interaction and risk perception.

[00:02:59] He is the past chair of the Transportation Research Board's Vehicle User Characteristics Committee and the Publications Division of the Human Factors and Aerogonomics Society.

[00:03:12] Dr. Horry received his PhD in engineering psychology from the University of Illinois at Urbana-Champaign.

[00:03:20] Moving at the speed of mobility, this is AutoVision News Radio with Carl Anthony in Detroit, Michigan.

[00:03:25] This latest study from the AAA Foundation for Traffic Safety is looking at the impact of changes to the posted speed limit on interstates and whether those changes are having an effect on nearby roads in surrounding neighborhoods or surrounding regions.

[00:03:43] We've been quite interested in the issue of speeding for quite some time and it really is because it's such a significant safety concern.

[00:03:49] According to NHTSA or the National Highway Traffic Safety Administration, speeding is a contributing factor in almost one-third of road fatalities over the past 20 years.

[00:04:01] And so it's really important that we understand how to improve the outlook when it comes to speeding, try to find ways of curbing this dangerous behavior.

[00:04:11] Adding to that, there's a lot of places that are changing their posted speed limits.

[00:04:16] So a lot of municipalities, states, regions are changing their posted speed limit and so we're really trying to get a better handle on the impact of those sorts of changes on safety and on the behavior of drivers as well.

[00:04:30] In the past, we've had a few different studies looking at the impact of differences in speed or differences in posted speed limit.

[00:04:36] In one study, we actually looked at how even small changes in speed can drastically increase the severity of injuries in crashes that occur.

[00:04:46] And so it's really important to understand that even a small five mile an hour change can really change the survivability of a crash.

[00:04:55] We've also looked at the impact of posted speed limit changes on a variety of different road types and looking at the impact on those roads themselves.

[00:05:06] And we found it's really kind of a mixed result.

[00:05:10] So in some cases, the safety outlook worsens when speed limits are increased.

[00:05:18] In other cases, it's not so clear cut.

[00:05:20] One of the limitations that we experienced with some of this past research is that when you look at just the road in which a posted speed limit change occurs, it might not reveal all of the traffic safety concerns when you consider the local transportation network.

[00:05:34] And so with the current study, we were really interested in looking at whether a change in posted speed limit on an interstate could have an effect on surrounding network and what we've seen in the past.

[00:05:45] And that was really the impetus for the study that we conducted here.

[00:05:49] In Iowa, where I grew up, Main Street was the benchmark for everything.

[00:05:55] When policies were enacted far away, the question on everybody's mind was how does that affect us locally in the town center on Main Street?

[00:06:04] And the first verse of Tip It On Back by Dierks Bentley from his 2012 album Home speaks to this very thing.

[00:06:12] And it's similar here with this study from the AAA Foundation for Traffic Safety.

[00:06:18] How does a change that is out of our control, how does that affect us on Main Street?

[00:06:24] Using a hypothetical example.

[00:06:28] Let's say that we were going to raise the speed limit on a road like Interstate 80.

[00:06:33] Would that impact the surrounding towns in an area like Southwest Iowa?

[00:06:39] This would be communities like Avocca, Walnut and Adair.

[00:06:43] Would they experience spillover effects?

[00:06:47] And how much say would they have or any town across the state have a spillover effect?

[00:06:54] And how much say would they have or any town across this great country,

[00:07:00] how much say would they have if a speed limit increase was proposed and on the docket?

[00:07:06] The AM radio broadcaster in me would want to understand these spillover effects and how they might impact us Iowans on Main Street.

[00:07:17] Spillover effects by definition are all unintended consequences of some change.

[00:07:22] In this case a change in the posted speed limit.

[00:07:26] It's really an outcome or a consequence that is observed in sort of a surrounding region or kind of a neighboring region

[00:07:35] that might not have been part of the initial intention behind a change.

[00:07:39] In the current context we're thinking about the spillover effect in terms of safety and crashes,

[00:07:46] speeding related crashes that are occurring as a result of a change in posted speed limit on an interstate.

[00:07:55] And so when we're looking for spillover, we're not looking on that interstate itself,

[00:07:59] we're looking in the surrounding region, some of the connecting roads, some of the neighboring streets and so on

[00:08:05] to see if we're seeing any changes in speeding related crashes as a result

[00:08:11] or that might be attributed to that change in posted speed limit on the interstate.

[00:08:14] In late July 2023 Iowa joined 10 other states in a speed awareness campaign.

[00:08:21] The measure was supported by the Iowa Governor's Traffic Safety Bureau with local law enforcement.

[00:08:26] News director Rick Hanson of KJA and Radio in Atlantic noted in his coverage at the time

[00:08:32] that Iowa experienced a dramatic 25% increase in speeding related fatalities from 2020 to 2021

[00:08:40] and in 2021 alone, speeding related crashes accounted for almost one quarter of all crash fatalities in Iowa.

[00:08:49] While going through this study on spillover effects from the AAA Foundation for Traffic Safety,

[00:08:55] it was impossible to ignore my Hawkeye State upbringing.

[00:08:59] From the perspective of a local community or township,

[00:09:03] we really want to be able to better understand the spillover effects

[00:09:06] because if they're facing an uptick or an increase in crashes,

[00:09:11] speeding related crashes as a result of a nearby change in posted speed limit,

[00:09:16] we really want to be able to pinpoint that so that we can look to improve things

[00:09:21] through maybe targeted countermeasures or some other initiatives.

[00:09:25] Now the current study focused on speed related crashes.

[00:09:29] It's important to note however that the current study helps us see

[00:09:32] or infer the effects of changes in posted speed limit,

[00:09:36] but it doesn't shed any insight into why it is happening.

[00:09:40] It could be due to changes in travel patterns,

[00:09:43] but also maybe some tendencies for people traveling on higher speed road

[00:09:48] to maintain those higher speeds when they exit onto local roads.

[00:09:51] We don't know for sure,

[00:09:53] but the current results really underscore the importance of looking

[00:09:57] in these surrounding regions when making changes in posted speed limits.

[00:09:59] We really need to better understand the broader impacts of these changes

[00:10:03] and how those impact safety.

[00:10:05] This research from the AAA Foundation for Traffic Safety on Spillover Effects

[00:10:10] looked at crash data before and after speed limit increases

[00:10:14] on interstates in Georgia, Oregon and Michigan.

[00:10:17] To do this we conducted what we call a hotspot analysis

[00:10:21] and we looked at kind of a region within a one mile radius of interstate.

[00:10:25] So it would be kind of all of the nearby roads to an interstate.

[00:10:29] And what the hotspot analysis allows us to do is to quantify

[00:10:33] and visualize changes in speed related crashes

[00:10:37] in the surrounding environment.

[00:10:39] And so you can kind of look in a region and see

[00:10:42] after a posted speed limit occurs on one road,

[00:10:46] does it have an effect in some of the surrounding neighborhoods,

[00:10:50] whether a positive or a negative effect?

[00:10:52] And this approach really allows us to really look down a corridor,

[00:10:55] a road corridor and kind of see how all of these changes

[00:10:59] are kind of showing up across the board.

[00:11:02] And really to get a better understanding of whether the spillover effect

[00:11:06] can be observed in some of the surrounding regions and neighborhoods

[00:11:10] following the change of posted speed limit on a major interstate.

[00:11:13] To mitigate spillover effects and reduce speeding,

[00:11:17] AAA recommends a multi-pronged approach that consists of public education,

[00:11:21] utilizing countermeasure technology like red light

[00:11:25] speed cameras and implementing new road designs

[00:11:29] that include narrower lanes and roadway landscaping.

[00:11:33] Complicating the matter is the perception of speeding

[00:11:36] versus other reckless driving behaviors.

[00:11:39] In its latest Traffic Safety Culture Index survey,

[00:11:43] AAA researchers noted that respondents viewed speeding

[00:11:46] as less dangerous than other risky driving behaviors.

[00:11:50] Less than half perceived speeding 15 mph or more on the freeway as dangerous.

[00:11:53] Speeding also had the lowest level of social disapproval

[00:11:57] compared to other reckless driving behaviors,

[00:12:00] and countermeasures to curb speeding

[00:12:03] had the lowest levels of support among survey participants.

[00:12:07] Ultimately more research is needed,

[00:12:10] especially when this disconnect between the dangers of speeding

[00:12:14] and public perception is placed in the context of spillover effects.

[00:12:18] When we looked at the available science concerning the spillover effect,

[00:12:21] we found a lot of mixed results.

[00:12:24] Some studies did show evidence of a spillover effect

[00:12:27] in local or nearby communities.

[00:12:30] Other studies found little evidence or perhaps some mixed results.

[00:12:34] And so what that really tells us is that there's much more work

[00:12:38] to be done in this area so that we can better understand

[00:12:42] the circumstances in which spillover effect might occur

[00:12:46] or if there's other factors at play.

[00:12:50] And our hope is that the spatial analysis that we conducted

[00:12:54] can be a tool that might be useful towards this end.

[00:12:58] When we look at our results of our analysis of Georgia, Michigan and Oregon,

[00:13:02] we found a lot of really interesting outcomes.

[00:13:06] Again, we looked at the period of time before

[00:13:10] a change in the posted speed limit occurred,

[00:13:13] and again this posted speed limit was on an interstate,

[00:13:17] but when you start to look out at the speed limit

[00:13:20] and look out in the surrounding environment,

[00:13:23] using this approach, looking at different little regions,

[00:13:28] you do see a lot of changes before and after

[00:13:32] the change in posted speed limit.

[00:13:35] And what we were mainly concerned with was the emergence of new hot spots.

[00:13:39] So looking at specific locations and seeing if crashes were now occurring

[00:13:43] where crashes were not occurring before.

[00:13:46] We also looked at regions where maybe the crashes

[00:13:50] were occurring both before and after or maybe with some slight changes.

[00:13:54] And we also looked at whether there was what we called historical hot spots

[00:13:58] where before the change in posted speed limit occurred,

[00:14:02] there might have been some crashes occurring,

[00:14:05] but after the change those seemed to have gone away.

[00:14:08] But importantly what we did find was the emergence of a lot of new hot spots

[00:14:12] across all roads and all case studies examined in this project.

[00:14:17] Overall, if we were just to look at the changes

[00:14:21] in crashes occurring on the interstates in these three states,

[00:14:25] we might not have concluded that there was any impact on safety.

[00:14:30] But really by looking at the local environment

[00:14:34] in this detailed fashion we were able to uncover

[00:14:37] some of these important safety effects.

[00:14:40] And really this is why we're really trying to underscore

[00:14:43] the importance of this broader perspective when we're looking at

[00:14:47] potential changes in posted speed limits and their impact on safety.

[00:14:51] And so this is another dimension that we're really mindful of

[00:14:54] and trying to promote public awareness of speeding

[00:14:57] to really try to make people better understand

[00:15:01] that it is a risky behavior,

[00:15:04] it contributes significantly to road crashes,

[00:15:07] and it's something that we need to work on

[00:15:09] in order to improve the safety outlook.

[00:15:11] To learn more about spillover effects,

[00:15:13] the Traffic Safety Culture Index survey,

[00:15:15] and the Iowa Governor's Traffic Safety Bureau,

[00:15:18] see the links in the show notes.

[00:15:20] AutoVision News Radio is available on Spotify,

[00:15:24] Apple Podcasts, Podbean, and more.

[00:15:27] In Detroit, alongside Dr. William Horry,

[00:15:30] I'm Carl Anthony, AutoVision News Radio.