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Wednesday
Jan092013

Do stroads cause more accidents?

The word “Stroad” has officially made it into the Urban Dictionary.

“Noun. Portmanteau of “street” and “road”: it describes a street, er, road, built for high speed, but with multiple access points. Excessive width is a common feature. A common feature in suburbia, especially along commercial strips. Unsafe at any speed, their extreme width and straightness paradoxically induces speeding. Somewhat more neutral than synonymous traffic sewer.”

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Driving a car is dangerous. In fact, it’s probably one of the most dangerous activities in your day. If you’re in a collision, you run the risk of death, injury or best case scenario, property damage and increased insurance rates. Many view this as an inevitable, albeit acceptable, consequence to modern life. And that is probably true. While it’d be naive to think design alone could reduce accidents, it can help.

What makes a street safe?

I think there are a lot of elements. The design is the first thing that comes to mind, and it’s followed by speed and traffic volume. I was curious to know how the stroad held up against other alternatives. To do this, I turned to my usual test lab: my hometown of Mankato. I examined Minnesota Department of Transportation crash data & AADT (average daily traffic volume) data in an admittedly non-scientific study.

Aerial1

I selected seven different road segments with comparable volumes and extracted crash data from 2009, 2010 and 2011. I picked the three most recent years available. I selected four stroads, two traditional downtown streets and a medium volume road connecting the west side of town with the university neighborhoods.

The below road segments are ranked by crash ratio. The more dangerous roads are listed on top.

Location Road Type Daily Volume # of Crashes Crashes per Day Crash Ratio
Madison Ave (Victory to Hwy 22) Stroad 16,300 165 0.15 9.24447E-06
2nd St (Warren to Main St) Traditional Street 6,500 58 0.05 8.14893E-06
Bassett Dr (Madison to Hwy 22) Stroad 6,000 34 0.03 5.17504E-06
Madison Ave (Dane to Victory) Stroad 22,300 71 0.06 2.90763E-06
Adams St (Victory to Hwy 22) Stroad 11,000 30 0.03 2.49066E-06
Stolzman Rd (Stadium to Blue Earth) Road 11,800 20 0.02 1.54787E-06
Riverfront (Bridge to Madison) Traditional Street 19,100 28 0.03 1.33878E-06

 

[Note: This is not a scientific study. I used MnDOT CMAT and MnDOT ADT data. Speed limits on each road range from 35 to 45 miles per hour. There were zero fatalities on these roads. Most crashes were not alcohol related.]

 The most dangerous road is Madison Avenue. This is Mankato’s Epic Stroad. It has 16,300 vehicles per day and 165 crashes. Compare this to Mankato’s traditional street, now a downtown thoroughfare, that has 19,100 vehicles per day and a mere 28 crashes over the same three year period.

Madison_victory-22

This stretch of Madison Avenue has 14 access points within less than a mile stretch. This number alone wouldn’t be bad if the access points were traditional intersections. In the past year, Strong Towns has pointed to how these access points cause congestion. And studies have shown that these formless, high-volume arterials may also be a root causes\ of accidents [see Safe Urban Form and Safe Streets, Liveable Streets by Eric Dumbaugh & Robert Rae].

riverfront bridge to madison image

Contrast Madison Avenue to Riverfront Drive. Riverfront Drive is a high-volume stretch of road through Mankato’s first downtown (now marketed as “Old Town”). Make no mistake, Riverfront Drive carries a lot of vehicles. In fact, it carries more vehicles than Madison Avenue with fewer lanes and fewer crashes. It also has on-street parking, sidewalks, street trees and the buildings address the street [Important Note: This segment of town is actually fairly unpleasant. There are lots of vehicles, truck traffic, some existing industrial activity, the buildings aren’t typically well-kept and there seems to be a high rate of business turnover – but, as urban planners say, it has great bones.

Stroads aren’t always less safe. Second Street in downtown and Bassett Drive both have around 6,000 vehicles per day, but Second Street has nearly double the crashes. Of course, maybe that’s because my mom has been padding the stats (Sorry Mom! I love you, but I had to post that).

2nd stImagine

When it comes to crash statistics, 2nd Street performs poorly. It ranks behind three other local stroads, including the road behind the Wal-Mart (I have no explanation for why this is the case). Bassett Drive is a collector that connects all things suburban–auto dealerships, both failed and successful big and small boxes, misplaced townhouses, gas stations and parking lots.

bassett_image

Bassett Drive is excessively wide and acts primarily as a way to funnel vehicles elsewhere. Yes, it’s safer than 2nd Street (as are two other stroads examined), but what good is it if the street doesn’t add any real value to the community?

Do stroads cause more accidents?

Academic research seems to indicate they do. In my brief Mankato-oriented research, with the exception of 2nd Street, stroads had higher crash ratios than traditional streets. Admittedly, my figures may be too simplistic. Crashes vary in severity, and being that there were few fatal crashes on Mankato roads, I wasn’t able to get a good gauge on the real danger of the selected roads (that’s a good thing by the way). As a society, fatal crashes are what we care about. Whether we like to admit it or not, as long as it doesn’t slow down our commute we really don’t care if someone gets into a minor, non-serious fender bender. These accidents cause minor economic damage, but they don’t yield protestors demanding something be changed.

Safety alone isn’t the best metric of how a street is doing. Don’t get me wrong, transportation safety is absolutely important. Yet, it can’t be an end in and of itself. I’m confident that everyone reading this would rather have a town full of crash-prone Second Street’s than any of the statistically safer stroads.

I mentioned above that while it’d be naive to think design alone could reduce accidents, it can help. But it’s not just the design of the road, it’s the design of the community, the buildings and the people. Now, we can’t afford to go around and retrofit our stroads. What we can do to stroads is simple, and again, you don’t need to be a rocket scientist to understand this.

  • Reduce speeds on stroads
  • Add on-street parking wherever possible
  • Re-stripe stroads to reduce excess capacity

It’s that simple and I guarantee it’ll work. Also, don’t text and drive!

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I would like to thank everyone on the Strong Towns Network who helped on this post. I still think it needs a little work, but it's much better than it would have been without you. Thanks. - Nate

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Reader Comments (5)

About a year ago, I was interviewed for a position studying Maryland police report data, and the interviewer asked me, doubtlessly expecting to surprise me, where I thought the highest accident rates were. Being in-the-know in the land use conversation, I of course gave her the correct answer (suburban arterials aka "stroads") and surprised her--I do not think she believed anyone who did not have access to that data could possibly know, or believe, that.

January 9, 2013 | Unregistered CommenterSteve S.

A recent Portland Metro safety report found evidence suggesting the answer is yes:

http://library.oregonmetro.gov/files//appendix_22_safetyreport.pdf

The biggest takeaways were that arterial stroads are where most of the serious crashes happen, the danger goes up with the number of lanes, and less congested roads also tend to see more crashes than congested ones.

January 9, 2013 | Unregistered CommenterCurt

I never liked stroads myself, long before I knew the word. Too fast, too dangerous. But I've also wondered, could multi-way boulevards be an acceptable alternative? Stroads certainly have (in many cases) the road width to create separation of local and thru traffic. Plus, boulevards have the benefit of being much more attractive.

January 10, 2013 | Unregistered Commenterpete-rock

I'm glad the relative severity of crashes was brought up, because that's a very important point, and a possible source of "lying with statistics" that can be troublesome. It's unfortunate that the threshold is merely fatal vs. non-fatal, because there's plenty of very serious but non-fatal accidents out there that get lumped together with the truly trivial. A multiple-car pileup that cripples several people, totals half a dozen cars, and takes out some utility poles that blacks out the neighborhood for the day is lumped in the statistics with the 5 mph rear-ending that doesn't even yield an insurance claim just because nobody died.

There's many scenarios where the safer environment actually appears less so because of the statistics. Take roundabouts versus a standard signalized intersection. In some cases (but not all) the total *number* of crashes may be a bit higher in the roundabout, but they're just minor fender benders, sideswipes, and other low-speed incidents. The number of serious t-bone and head-on collisions in the roundabout is reduced to zero, so it's a big gain in safety despite the actual number of crashes. Parking lots are a similar in that there's lots of crashes, but they're all low-speed and mostly trivial. I'd imagine if you could better parse the data (if only it were that easy!) you'd find that 2nd Street and Riverfront are also mostly low-speed crashes, usually involving cars maneuvering into and out of parking spots or driveways, which yield few if any injuries, while the relative severity of the crashes on the stroads is worse even if there are a similar number either in aggregate or proportionately.

January 11, 2013 | Unregistered CommenterJeffrey Jakucyk

Pete-rock: That is the question, isn't it? MWBs, like stroads, are compromises between road and street functions. Examples abroad (mostly in Europe) suggest that MWB treatment is viable for corridors ranging all the way from city centers out to inner suburban environments--say a 1000 ppsm population density as a cutoff. The idea is that, unlike stroads which dedicate a majority of the right-of-way to moving cars quickly but then brake them with stoplights, MWBs only dedicate a portion--ideally about half (if not less; the most minimal true MWB could have no more than 1/4 of the ROW dedicated to this purpose)--to moving cars quickly; the remainder is made a street realm via the use of Dutch woonerf principles; that is, the space is shared. Value creation then happens along the access ways, while roadway functions are shunted out to the most open part of the ROW.

The real answer is we don't really know. European examples offer us guesstimates, but until we start really implementing them here we don't know what'll work for us and what won't.

Note, by the way, that since in 99% of cases, stroads are naturally unsafe, unproductive environments, their replacement where MWBs cease to be viable are country highways, possibly with bicycle sidepaths if mean density supports it. (For example, York County, PA is a densely rural environment; Elk County in the same state is just plain rural.) These are clearly demarcated from the Main and Broad Streets of the towns and villages they run through by narrowing the driving lanes, and possibly with some kind of "gateway feature" to make clear you're entering town--like a traffic circle, for instance. Signs aren't enough.

Beyond that, I think a major question we need to be asking is "what constitutes a productive environment?". Clearly, the combination of very low population densities and extremely wide streets doesn't; by narrowing the street, you reduce its long-term maintenance obligation, which then increases its rate of return relative to existing assets; the same can be said for any large-scale infrastructure. Do we really need to be running water lines out to developments on 2, 3, 4, or 5 acre plots? Just by looking at the numbers, it's clear we're either going to need to raise lots of places' property taxes 200% or unbuild their infrastructure, just to get spending (maintenance obligations) in line with income. We're not talking about discretionary spending, either, like social services or corporate welfare; we're talking about making sure clean water comes out of their spigots, the lights come on at night, and that they can get from home to work.

January 12, 2013 | Unregistered CommenterSteve S.
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