(Unedited) Podcast Transcript 464: Narrow the Lanes!

This week on Talking Headways we’re joined by Dr. Shima Hamidi, Assistant Professor at Johns Hopkins University to talk about the report: A National Investigation of the Impacts of Lane Width on Traffic Safety.  We chat about the data they collected for 1,100 streets, how narrowing streets can create more space for bikes and peds and how the study and determined narrower lanes are safer.

You can listen to this episode at Streetsblog USA or at the hosting archive.

Below is an unedited AI generated full episode transcript:

Jeff Wood (44s):
Dr. Shima Hamidi. Welcome to the Talking Headways podcast.

Shima Hamidi (1m 25s):
Thank you Jeff for having me.

Jeff Wood (1m 27s):
Well thanks for being here. We had you on episode 99 with Reid Ewing who also worked on this paper as well and and John Reni and that was back in 2016. So how have you been since 2016?

Shima Hamidi (1m 37s):
A lot happened since then. I moved to Baltimore to Johns Hopkins University and my work has been shifting more toward transportation and health, health Impacts of transportation and built environment. And recently we got a $10 million grant to launch a new center on climate change and transportation, which we are really excited about. So this language project is kind of part of that. We’re working on the expansion of this project in the new center and hopefully many more to see in the next five years.

Jeff Wood (2m 13s):
That’s awesome. you know, one thing I asked folks, and I don’t know if I asked you this last time you were on the show, but I wanna know how you got into transportation and public health even. How did you like kind of make that connection? And was it when you were a young child or was it something that happened later on in life?

Shima Hamidi (2m 27s):
I think it always was fascinated by, by transportation. I am from Iran and public transit is a, a huge deal there for probably the largest mode of transportation. And so I used to take transit whenever I wanna go, a great metro system. So when I came to the US in 2011, I was kind of surprised to see kind of, you know, look at the portion of commuting or transportation that’s done by driving relative to public transit or walking or biking. And I wanted to learn more and see, you know, why is this patterns of commuting or transportation dominant in the us And I was so lucky to be able to work with  Reid Ewing was my advisor, Dr.

Shima Hamidi (3m 18s):
Dissertation and study advisor and still co-author on most of my, my research and work. And you know, he is one of the top Transportation experts in the us so we get to work together on different aspects of Transportation and that, you know, is something that continued to be the case from 2011 today.

Jeff Wood (3m 40s):
And you moved recently from Arlington to Baltimore. How’s that change been?

Shima Hamidi (3m 44s):
A huge change. Unbelievable,

Jeff Wood (3m 49s):
I should say Arlington Texas.

Shima Hamidi (3m 51s):
Arlington Texas, yeah. Yeah. So I did not have a driver license before going to Arlington, Texas. Even in Salt Lake City, Utah. I used to take transit and light Rail whenever I wanted to go in Texas. I was totally, you know, relying on car and driving and I remember when I wanted to go to Texas, everyone was telling me before you get a house, buy a car. And that has not been the case here in Baltimore, you know, even though I, I still, you know, kept my car, but very rarely I, I’m using that to go to work, to go to major destinations, my daily destinations.

Shima Hamidi (4m 33s):
I don’t need to drive and I like it very much.

Jeff Wood (4m 36s):
Yeah, I can imagine. Well, let’s talk about your report, a national investigation on the Impacts of Lane Width on traffic safety narrowing Travel Lanes is an opportunity to promote biking and pedestrian facilities within the existing roadway infrastructure. That’s quite a mouthful of a title, but I, I like it. I wanna dive into the report. I wanna start where the idea of Lane Witts come from, like the basic background of the Width of streets. Who initially decided what witts were appropriate and how are they implemented?

Shima Hamidi (5m 4s):
Hmm, great question. So the standards on LA Lane widths has, has not changed for years, for decades. It goes back to well before 2000 where really the, the main source that everyone is relying on for these standards is the green book, which comes from the associations of civilian traffic engineers and state dots reps. And it’s kind of has been traffic engineers call it the Bible and it, it’s really the book and the standards that everyone is referring to, everyone is citing that and everyone is using that almost in every state that you look.

Shima Hamidi (5m 52s):
And the standard that is there typically is looking for 11 or 12 foot for arterials as the minimum. So we’ve interviewed several state dots and really looking at the process that they used to to make decisions on language and most of them just have been telling us that we rely on Ash to Green book.

Jeff Wood (6m 17s):
Do you know where the Lane wits and the Ashton Green Book came from? Was it a, a kind of a panel of quote unquote experts that were putting things together?

Shima Hamidi (6m 24s):
I’m not sure about where it goes back to to those standards. I can’t just compare that with standards for example in Europe and that’s way wider than European streets for the same road class in Europe, the average lane Width is 8.2 foot and here, here we have minimum of 11 to 12. And so if you think about that three foot extra per lane that we have here, and if you just multiply that by the number of lanes, it’s exactly the amount of space you need to add a bike lane, which is not happening here in most cities.

Shima Hamidi (7m 9s):
But again, other countries, other developed countries with a fraction of traffic fatalities of the US have been doing that and have absolutely no problem.

Jeff Wood (7m 20s):
We recently discussed the topic of traffic safety with Kerry Watkins and David Eder and, and their idea of a safe systems pyramid. And one of the main things I took from that discussion specifically was greater speed and kinetic energy creates more potential for traffic deaths. And so one of the ways we designed roads, and I read this in your report, seems to be the complete opposite idea of being more permissive about speeding. So we, we allow people to speed and we think that designing roads in a way that allows a little bit more speeding might be safer. I’m wondering if You can kind of expound upon that and maybe where that idea comes from.

Shima Hamidi (7m 53s):
Yeah, exactly. Jeff, you, you just put it together beautifully. The traditional traffic engineering mindset is that we should design roads in a way to minimize errors, minimize the error of drivers. And so their justification is that wider lanes and several other design features that make driving fast and convenient would minimize drivers error. But I mean there is this new, new approach that mostly transportation planners and urban designers advocate for that says we should design the streets in a way to take care of the most vulnerable users of the street, pedestrian and cyclists.

Shima Hamidi (8m 42s):
And if we take care of them then drivers also will be safe. But if you look at the streets in the us historically all the way back to fifties and sixties and even now in most cities, what you see is the quiet opposite streets that are wide with minimum level of complexity and the number of objects on the street that you know, again with this mindset that they call it forgiving driving or forgiving design to make the drivers error minimal. But again, when you look at the number of crashes and fatalities, it shows that it’s quite opposite.

Shima Hamidi (9m 28s):
Just as you, you mentioned US has one of the highest rates of traffic fatalities by far like four times more than other countries, other developed countries, traffic fatalities is the leading cause of deaths for people age 16 to 54. And you know, it’s just getting worse and worse even for pedestrian and cyclists remember reading somewhere that 2020 just marked the deadliest year for pedestrians in 40 year history of tracking pedestrian fatalities. So all of these numbers are telling us that that doesn’t work. Drivers are so sensitive about the environment surrounding them and so if the environment doesn’t give them the sense of safety or you know make them to be more cautious, then they, they gotta drive slower and that will reduce the, the chances of traffic crashes and fatalities.

Jeff Wood (10m 24s):
And that’s something you talk about in the report is kind of that built environment factors make a difference, street trees building setbacks might have an impact. What made you wanna kind of think about those in addition to Lane Witts as something that might impact how fast or or slow people drove?

Shima Hamidi (10m 39s):
Great question. So if you think of two scenarios, one is you are driving on a road that is in a rural area, nothing happening in any side of the street. There is no trees, no objects, nothing else, no sidewalk, no bike lane versus a similar street in the same class, same lands, same speed limit. But in downtown area on the first case you are gonna just speed up as a driver and just go fast because you have this sense of safety sense of nothing is gonna happen. All of those items, design factors on the second scenario, the downtown street that might give drivers the sense of busyness complexity and make them to drive more cautiously are the factors that we try to control in this study.

Shima Hamidi (11m 37s):
So factors such as tree coverage, pedestrian furniture with soft sidewalk, number of Lanes, street setback, traffic calming devices in the street even we had a variable that would measure the sense of motion in the street. Like how how much you have other users of street like pedestrian and cyclists on the same street sharing space with cars, which again make drivers drive slower and more carefully. We try to control for all of these factors in addition to language.

Jeff Wood (12m 13s):
So then what did you find when you put all these things together?

Shima Hamidi (12m 17s):
We found that again first the context matters. So again, that street, there’s a huge difference between the street on that rural area with no complexity or street objects versus all of these 21 design factors that we control for. And when you control for all of these factors, then you see that not only lane Width or narrower lanes don’t increase the number of crashes in many cases actually it’s quite the opposite. You see that wider lanes are more dangerous experience, higher number of crashes than their narrower counterparts.

Shima Hamidi (13m 2s):
And I’m talking about for example, 12 foot lanes versus nine or 10. We found that 12 foot lanes have actually significantly higher number of crashes than nine or 10 foot lane, which is counter to the street design practice and most policies and language standards that you see currently happening in the us.

Jeff Wood (13m 24s):
And to clarify this is non intersection collisions that you looked at as well. Something that I think a lot of folks will look at the collisions and a lot of them happened at intersections, but this is on roads depended on lane widths and then also it’s the non intersection crashes, correct?

Shima Hamidi (13m 39s):
That’s correct. About 40% of crashes happen in the intersection and we did not include them because Lane Width really doesn’t have anything to do with intersection. And so there are a bunch of other factors that might affect crashes at the intersections, but you know really what the lane Width or number of lanes could impact how many non intersection crashes you see across the street. And that was the outcome variables in this study

Jeff Wood (14m 11s):
And the speeds had something to do with it too. The speed limits on the streets I imagine?

Shima Hamidi (14m 16s):
Absolutely. So we also broke down the sample street samples that we had in our study, which is more than 1100 streets from seven different cities to different speed classes. And the most interesting findings we had were for the street with the speed class of 20 to 25 mile per and 30 to 35 mile per hours for 20 to 25. We found that different language values have absolutely no difference in terms of number of crash. It doesn’t matter if it’s nine foot, 10 foot, 11 or 12 foot, we think that’s because at 20 to 25 miles per hour the drivers are slow enough that lane Width differences might not impact the likelihood of crash happening.

Shima Hamidi (15m 11s):
But when you go to 30 to 35 miles per hour, absolutely different, you will see that 12 foot Lanes and 11 foot Lanes have significantly higher number of crashes than 10 or nine. And that’s why we think that’s the speed class where you begin to see the why their lanes give drivers the sense of safety and likelihood of higher speeds that might lead to higher number of crashes.

Jeff Wood (15m 44s):
You know what’s really interesting about that finding at the 30 to 35 mile per hour level is that you always see the chart of pedestrian collisions and fatalities and the possibility of serious injury increasing around that level, right? When you get past 30 miles per hour, that’s when the curve goes up significantly from that collision aspect with pedestrians and cyclists. So it’s interesting to see how that works actually with the lane widths too, where collisions become more prevalent when you get past that kind of, that 30 mile per hour threshold, that high 20 mile per hour threshold.

Shima Hamidi (16m 17s):
Yes, I think the two actually correlates when you see that as you move toward 20 to 25 to 30 to 35, the number of crashes increase and the number of crashes pre increasing lane Width also increase. And I wanna say that this road class 30 to 35 actually is the best candidate for adding a bike lane or sidewalk because it’s typically, it’s not a residential area, not a local road, but it, it’s in a mostly arterials or principal arterials where you see they are connecting busy parts of city together and typically are most more likely to be used by pedestrian and cyclists.

Shima Hamidi (17m 6s):
And so you see that this is the, the class that is the highest potential for bike lane and sidewalks highest number of crashes compared to slower speeds and also typically wider lanes.

Jeff Wood (17m 20s):
Yeah because the engineers have decided that they want people to be safe going faster, right? That’s the, that’s the trick.

Shima Hamidi (17m 27s):
And you know when that mindset of yeah, let design streets to help drivers for a convenient and fast driving comes with this components of we design designed streets for fast driving and whenever we wanna slow down the traffic, we’ll use the speed limit posted. Speed limit never works. If you wanna make that work you have to have 24 7 monitoring traffic and having enforcement in place, otherwise drivers aren’t gonna speed up if they can, if they get the opportunity, if they have this sense of it’s okay, speed limit is not gonna be forcing drivers to make that speed actually work.

Shima Hamidi (18m 15s):
And so how about not going with the speed limit and going with the design features of street to come up with the, the speed that we have in mind for that specific street. That’s really what is the foundation for this study and this line of research that has been done before.

Jeff Wood (18m 36s):
That’s a question I was gonna ask you was like you found that, you know less than 25 miles per hour, there’s really no collisions and no connections between the lane widths. So do we just need to post every street at 25 miles per hour or is it something that they could actually matter in that context but it just doesn’t show up in the data that you looked at?

Shima Hamidi (18m 54s):
So for, you know, the, the way the the hierarchy of street classes work is that you have freeways and highways, then you have arterials, then you have major and minor collectors and local streets, typically local streets or minor major collectors have 20 to 25 miles per hour. If you use 20 to 25 miles per hour for arterials, then you are gonna end up with congestion or other similar challenges of slow traffic on those streets. Again, the point is that speed limit is not the solution for designing and planning and executing a specific driving speed for, for a specific street.

Shima Hamidi (19m 42s):
We have to go with the design, we have to go with the design characteristics, with all those objectives, all these features that we’ve included in this study that comes actually from literature, 30 years of literature on traffic safety and design features, all of this, every single of this could make a difference and all together is what can make the driving speed close to what the design speed is for a particular street.

Jeff Wood (20m 12s):
You also make a specific distinction for larger trucks and buses and, and I’m curious about that finding as well

Shima Hamidi (20m 19s):
For transit corridors for example, we’ll see that the transit vehicles such as bus or even shuttles typically are wider than a regular car. And so you see that nine foot or even 10 foot might be a little bit challenging for the drivers like, like bus drivers and you see that in in the literature as well that the lanes that are Narrow could be particularly challenging and increase the number of bus related crashes. And so for areas that you see are transit corridors, not every street is a transit corridor.

Shima Hamidi (21m 0s):
Most streets are not transit corridors. For those that are transit corridor, we think that nine or 10 might not be, you know, the best optimal language. The same for trucks or freight transportation. We had a conversation with Oregon Department of Transportation officials and they were mentioning that freight transportation is a big deal and a huge industry there. And so even though sometimes they wanna go with narrower lanes, but they have to accommodate the size of freight and trucks and larger vehicles on those corridors.

Shima Hamidi (21m 44s):
But again, we are talking about a small portion of streets on the street network for most streets we can, our recommendation is that nine or 10 foot would work.

Jeff Wood (21m 56s):
You did have extensive discussions with state DOT officials. I’m wondering what you learned from those discussions and what stuck out to you as something interesting?

Shima Hamidi (22m 4s):
We had great conversations. I think we had interviews with five state dots and I can mention a couple of key findings we had with we Vermont DOT. We were actually, you know, surprised to see that we, Vermont was one of the first states in the us I think it goes back to early 2000 or late 1990 to have a legislative past mentioning that if you go with nine foot lanes, first of all they, you require the DOT to come up with their own design standards instead of going with Aashto to have something that you know kind of fits the needs and requirements of bare Vermont streets.

Shima Hamidi (22m 50s):
And second, to give permission to DOT to go for, for nine foot lanes without being liable if something happens because that’s one of the most important or serious, you know, concerns. We, we found in our conversations that there is a issue of livability. Vermont didn’t have that in the past 25 years, but not even a single street with a nine foot lanes have been built nothing, not even one case. And again, there were concerns with the nine foot lanes being too Narrow, the likelihood of increasing number of crashes and sometimes really the convenience of going with wider lanes just to follow the standards that everyone has been following for years.

Shima Hamidi (23m 45s):
The same across the other states too. We found that in most states still aashto is the case, 11 to 12 foot lanes are the dominant forms of or standards for language and states have this exception rule that if there’s a specific street that we wanna do narrower, we go through the exception. And there there’s a criteria for, you know, how the exception would happen, very rare cases of exception. And so when we ask why, again as I mentioned the issue of livability, lack of data, lack of information, this general hypothesis that wider is safer in most cases is something that we, we observed across our interviews with different state dot some states begin to revise these standards and go with narrower.

Shima Hamidi (24m 46s):
One of them was Florida DOT, which told us that they, they have this new design manual that I think they just released in 2023 that actually has nine foot lanes as one of the design standards for roads that are in downtown areas. And they have a criteria for how to specify nine foot lanes, but they have it and they are actually implemented in several cases that they mentioned to us. So that was great to hear. And see,

Jeff Wood (25m 20s):
It’s so interesting because you hear about this all the time, the livability and so everybody basically will use the green guide, the Aashto green guide because it reduces their livability. But on a whole, it actually increases the amount of collisions it feels like because of the findings that you all had, which is basically that the wider lanes mean more collisions on linear sections of road. And so it’s kind of interesting to see how your report is kind of pushing back on that argument that state DOT officials, traffic engineers are gonna have that, you know, we’re just trying to reduce our livability. I’m wondering at what point does somebody sue Aashto or somebody because their standards mean more collisions. I’ve been waiting for that for quite a while because I feel like there’s gotta be a change somewhere because we can’t keep going the way that we’ve going with 40,000 deaths on the roads every year.

Shima Hamidi (26m 6s):
Absolutely, absolutely. And I I wanna say that, you know, this is a national study. Like this is a study that is not for a specific road or a specific city or a few number of streets in a city. It includes 1100 streets, it covers more than 21 design features and you know, the data says wider Lanes are more dangerous, wider lanes increased the number of crashes. And something we heard over and over in our interviews with state DOT was that they wanna see the data. They are very interested in seeing what really the, the quantitative analysis and the data says.

Shima Hamidi (26m 50s):
Several of them ask us to send them over the report and the analysis and they were receptive to give you an example, Caltran, California Department of Transportation to really consider looking at their standards and changes in its standards if we find that the data says quite counter to the general belief. So I think at least at the state level, most likely at the city level with city departments of transportation, we see a lot of interest across the country to go for more multimodal transportation bike lanes and sidewalks and narrower streets.

Shima Hamidi (27m 32s):
Hopefully we’ll see some changes happening.

Jeff Wood (27m 35s):
I wanna know more about how you collected the data. What did you use, what forms of data did you use to put together the massive spreadsheet or, or Airtable or whatever it was you created to put together this report?

Shima Hamidi (27m 47s):
That’s a great question because one of the reasons that this topic is, is not widely studied and the reason is data availability. you know, when, when you look at traffic volume data is available most often You can get it from a state dts. It’s very hard to get data on microscale design features of studio. You have to do the data collection and it’s very hard to do that and time consuming to do that. For 1100 streets, thanks to our supporter, the Bloomberg Philanthropies and Bloomberg American Health initiatives, we were able to work with computer scientists and programmers to come up with machine learning techniques to look at Google Street maps and Google errors and Google views, train the machines to look at a sample of cases, sample of streets, and to be able to measure most of these variables automatically for the streets for some others, including language, we still had to do it manually, but for most of our variables we either did the machine learning and trained the computers to get the data for us from those sources or for some of them, such as traffic volume, we were able to get it from state deities.

Shima Hamidi (29m 10s):
But yeah, that gives us a, a really rich data sets. I mentioned the expansion of this project now in, in our center to be able to look at other outcomes, not only the number of crashes but also the severity of crashes, how fatal are those crashes and other environmental features, walkability, livability of streets. So we have a series of outcomes that we are now linking to, to that data set. And that’s gonna be the new analysis that will be the follow up to, to this original study

Jeff Wood (29m 47s):
With all those, you know, self-driving car tests going on and all the LIDAR data that they’re collecting. I feel like if you could get access to that, that might actually open up a huge possibility for measuring every street in the city, every street in, in a region because there’s, they’re ubiquitous, they’re everywhere, at least here in San Francisco, they are until crews stop, stop operating for a little while obviously. But I feel like that’s a, that’s a rich trove that might be mined at some point.

Shima Hamidi (30m 12s):
Oh I would love to get my hands on on that. That would be an an amazing opportunity to, you know, for now we have a methodology that we can use to measure these design features for any street. And with that then we’ll have information on driving behaviors on speed, actual speed, not speed limit and actual traffic volume. And that would be a a, a very cool information and analysis that will definitely will be a huge improvement over what we have now. Yeah.

Jeff Wood (30m 52s):
How did the pandemic impact your study?

Shima Hamidi (30m 55s):
It did not because the years of crashes we include as 2016 through 19 by purpose we excluded pandemic because during the, the, the COVID-19 pandemic, we saw an unusual patterns of travel driving, walking and biking and number of crashes. And we wanted to come up with an analysis that’s more generalizable than the pandemic area. But again, that’s a study that could be done using the same methodology for the pandemic time as well.

Jeff Wood (31m 30s):
So with these findings, the lane witts are crucial in thinking about traffic speeds as well as collisions. I’m wondering how hard it will be to kind of convince folks that this is an important kind of way to move forward on trying to reduce traffic collisions. One kind of example in Texas is, you know, San Antonio was, was working on trying to do a road diet in the city and they had actually gotten the road back from TxDOT, but then politically things got really messy in this and it was even, you know, allegedly the governor mentioned that he didn’t want this to happen and so it didn’t happen. And so I’m wondering how like politically this can actually move forward in a way that’s meaningful and helpful for reducing traffic collisions.

Shima Hamidi (32m 11s):
Definitely the political environment’s gonna play a, a big role. We’ll see some states are more receptive to lane narrowing to overall multimodal Transportation walkability and ity than others. And so my hope is that we’ll have states that are more toward active and green transportation to begin, you know, implementing our findings and going with Narrow lanes and eventually we’ll see that when we see the improvement in traffic safety in those states will have other states as well joining, you know, the league, I wanna say that as you mentioned, safety is a big deal, but equally important is having an opportunity for bucking and biking.

Shima Hamidi (33m 4s):
So sometimes this additional space is make a difference between having a bike lane or not having a sidewalk or not. And I’ve interviewed many bicyclists that wanna do biking in the city but are just afraid because there is no biking infrastructure. And so I think this is probably the most cost efficient way, the most feasible way to add bike Lanes and wider sidewalks to the existing infrastructure while improving safety.

Jeff Wood (33m 41s):
And the bike Lanes actually help reduce collisions as well because of the Width, right?

Shima Hamidi (33m 46s):
Absolutely, absolutely. So the bike lanes, so that will be like, I think kind of the dabble role of lane, which narrowing on safety because that bike lanes will improve safety for bicyclists and for drivers as well. So you will see the fewer number of crashes happening or crashes, bike related crashes happening in the street. We are doing not good in terms of bike lane coverage in the us. Jeff, I don’t know if you’ve been following, but I was surprised to see that for example, the city of Dallas has only five miles of protected bike lanes, which is, if you imagine how much You can bike with five miles, really nothing.

Shima Hamidi (34m 30s):
Other cities as well, like New York is like a paradise for walking and biking and only 8% of New York streets have bike lane, protected bike lane. And, and so I think as important as improving safety is really giving opportunity for to people who wanna bike and walk to be able to do that and language will give us that opportunity.

Jeff Wood (34m 52s):
What’s been the reaction so far to the research

Shima Hamidi (34m 56s):
Positive? We were contacted by several cities in Washington, in California, here in Maryland that were interested to see more specifically what does it mean for their city or how they can find the most immediate candidates for language reduction. And I think that’s a, a very, very positive sign of having this conversation got started and even some cities moving toward rethinking their language standards or language reduction projects. Salt Lake City in Utah, for example, was one of the cities that were super interested and we had conversations with them that they mentioned if You can provide us with the list of streets that are good candidates for language reduction, we are gonna include them in our plan and go for language reduction actually on those streets, which I think that that’s an awesome thing to hear.

Jeff Wood (35m 59s):
That’s awesome. Where can folks find the report if they wanna get a copy?

Shima Hamidi (36m 3s):
There’s a website I can share with you the link of the website that has the full report has the key findings, Narrow length at American Health do jsu.edu is where Yvonne and his team, they created this beautiful website with our full report as well as key findings and the key implementation points for cities and and states.

Jeff Wood (36m 34s):
Awesome. Well, Dr. Hamidi, thanks so much for joining us. We really appreciate your time.

Shima Hamidi (36m 38s):
Thank you, Jeff. I appreciate your interest in this study and I’ve been following up your work and I’m a fan and a pleasure talking with you.

Jeff Wood (36m 45s):
Well, let’s not wait seven years to talk next time.