Traffic studies; useful or junk?
 

You can read what StreetsBlog thinks about them here. My very small city relies on them, and they do tend towards apocalyptic levels of future traffic. Thinking about sending this to our City Engineer for him to ignore. :thumb:

I recently read Charles Marohn's Confessions of a Recovering Engineer, he has similar feelings toward them.

I see Streetsblog is again pointing fingers at traffic engineers to keep their activist readership riled up (Disclosure: I was one of their favorite piñatas for several years.)

Nearly every public works or transportation agency has policies or guidelines on what they expect to be in a traffic impact analysis (TIA). If the agency expectation is for the developer to fund infrastructure to accommodate motor traffic, the guidelines (and how they're applied) will reflect that. If the agency expectation is for the developer to instead discourage motor traffic accommodation and instead provide improved access for other modes, the guidelines will reflect that concept.

The guidelines typically reflect the agency culture, which is set by senior management and by political oversight, not by the guy hired to write & seal the TIA. If a practitioner decides to go against the guidelines, regardless of motive, they're likely to get summarily rejected (often repeatedly) and have a very irate developer for a client.

Change in agency culture isn't easy, but it can be done if it's made clear and followed through by the folks in charge. Blaming the engineers in the middle is easy, but doesn't change much or get the desired results.

a pretty thin piece by streetsblog, IMO. i certainly agree that there are issues with the way transportation planning is handled in most of america, but RCMoeur is completely correct that lead agencies have policies and priorities which are generally set by electeds. this is the problem with blaming engineering for anything: engineering is a tool. the key question is, "what are we trying to achieve?" i don't ask my colleagues to come up with a collection of beams and columns and frames and walls that they think is fun and state of the art, i ask them to come up with the lightest, lowest carbon, least expensive structure which supports a certain amount of load/use in a certain shape. the analysis and subsequent engineering design is the tool by which said goal is achieved.

if the goal is to move more cars more quickly, studies and subsequent engineering and construction can do this, to a point. human piloted automobiles of low occupancy are an INCREDIBLY inefficient way to get people around, and i believe induced demand is very real, so we need to start with policies/goals that discourage the use of private automobiles to the extreme. many cities have such policies, and in these cases the transportation studies will find substantial impacts from developing, resulting in worsening traffic, resulting in mitigation measures which may do some good as well as overrides to either allow or disallow development.

before san francisco shifted away from an intersection based methodology, it was pretty much par for the course than ANY project would have a significant and unavoidable impact on traffic and correspondingly air pollution, and those impacts would be acknowledged and the project would move forward anyway. the city's policies are explicitly transit first, correctly acknowledging that no densely built urban area can accommodate even half of it's residents using private vehicles as their primary mode of transportation.

Fortunately Arcata is focusing on infill; of necessity as there's nowhere to sprawl to, so (almost) no new roads at least. The trouble comes with our City Engineer; nice guy, rides a bike, but professionally he's all about moving cars quickly. Our five-member city council depends on him as an expert, so when he shows them the traffic study with apocalyptic levels of future traffic, they take him at his word. So when the Engineering Dept. comes up with a bad idea, the council usually agrees with him.

I'm currently reviewing the Transportation Element of the Draft General Plan. Fingers crossed the worst of the car-centric parts have been revised.

EDIT: I managed to forget for a minute that Engineering is still using LOS instead of VMT. ::facepalm::

My standard disclaimer--I know next to nothing about this kind of engineering and realize you're an actual expert. I will not be upset if you point out that something I say is stupid as I am well aware of the Dunning Kruger effect. My knowledge, such as it is, comes basically from having studied administrative law and bureaucracy.


I don't think what you just wrote actually contradicts the article--basically, that the guidelines chosen will reflect the contracting agency's policy preference so that the TIA is not actually an independent piece of evidence that is of much value. If I'm not wrong, I think what's happening here is that the paper this article was based on was arguing that the agencies, courts, etc. trying to figure out whether the TIA actually is valid need to know more about the assumptions and methods used to produce the projections. Otherwise, the engineer is really in the role of the for-hire expert witness, and it's widely known just how manipulable the findings of those are.

There's a link to the paper hidden in the op article, and it contains a lot of methodology criticism that I'm definitely not qualified to assess. It'd be interesting to get your take on those; https://papers.ssrn.com/sol3/papers....act_id=4388704
There's a link on that page to download the pdf of the paper. I'm not paying $50 to see if it's much different from the published version.

My understanding is that a lot if not most of these TIA are basically checking a box on requirements of various Administrative Procedure Acts (state and federal) that require documentation of substantial evidence or at least demonstrating that there was at least some evidence supporting the decision (not arbitrary or capricious).

My personal experience with traffic studies is consistent with this.

I obtained the TS done for a new apartment complex which I was concerned would have safe access issues. There was no discussion in the study about individual movements in and out of the complex. In this case, residents may be tempted to make dangerous (and btw illegal) turns to avoid long detours.

The pre-print paper is focused on counts.

To a layman the terms TS and TIA imply a deeper analysis than was actually done in the studies I examined.

I'm not familiar with that particular manuscript, nor have I purchased it. But I will say as a peer reviewer, any manuscript with biased wording or a title or abstract that has strong advocacy-focused language (as this one does) would be reviewed critically by me, as my experience with such papers leads me to think it's very likely the manuscript is not an objective analysis, but instead either an advocacy position or a sales pitch. Once an author is identified with a strong advocacy position, their objective credibility is permanently affected. Unfortunately, many research review committees have been taken over by advocates from particular viewpoints, with committees becoming monocultures of groupthink and systematic removal of experts with differing opinions - all in an effort to "improve consensus".

Jeez, that's not much of a basis for critiquing the manuscript. As a trial lawyer, I don't find the phrasing of the title unreasonable at all--there are supposed to be standards for what constitutes expert scientific evidence in court. Asking whether the methodologies employed are actually scientifically sound is a very reasonable question and there does appear to me to be an argument made in the free pre-print manuscript that can be downloaded from the abstract page that the methodology employed in most TIAs will over-predict vehicle traffic issues systematically. I don't feel qualified to judge the quality of the argument, but simply dismissing it because it sounds " biased" or advocacy based just sounds like defensiveness for your profession. The accusation is that members of your profession are basically functioning as "advocates for hire" who make it seem as if a particular policy decision is based on scientific analysis. Dismissing that accusation as mere advocacy is begging the question. I think it's unreasonable to dismiss this study as a product of "groupthink" without actually "reviewing" its content rather than whether or not you agree with its tone or thesis.

Sorry if it seems like I'm telling you to defend your profession, but your posts here are volunteering to do just that exactly. I mean that if you're implying that advocacy groups are clearly wrong because they consist of advocates, you're definitely posting on an inhospitable forum.

It seems you read a lot more into what I wrote than what I wrote.

My peer review assignments are for research, where there is (or at least should be) an expectation of objective and thorough collection, analysis, and presentation of data and findings in order to advance knowledge and practice. These types of manuscripts (and alas there are many of them) are trying to argue a specific position, and are typically dismissive of or antagonistic to opposing positions. An article that analyzes issues with TIAs from an objective or evenhanded viewpoint might be much more useful in advancing the state of the practice. Instead, the article could be seen as polarizing.

You mention your profession is trial law. That would seem to be an example of where practitioners routinely take a "I'm right, you're wrong" approach, where objectivity and improvement in engineering practice might be accidental but unlikely byproducts. I will say that in my review of expert testimony in cases involving traffic issues, I've noted that the more the expert tries to sound like an advocate, it seems to be a "pounding the table, not the facts" approach.

It's not my job to defend my profession. That seems to be your imposition on me. I am providing commentary on the issue(s) in question based on my knowledge and experience. And there are practitioners out there who make better money than I do writing TIAs that say what the developer or agency wants instead of a thorough and objective assessment of impacts. But the way to address that is through better guidance stating clear expectations.

If it wasn't your intent to defend your profession, I have no idea what the point of post #3 was supposed to be. It sure reads like "don't blame the engineers, talk to the people who are hiring them". I can't help but notice that rather than actually discussing the subject raised (the evidentiary value of traffic studies or lack thereof) you have stated you haven't actually looked at the underlying research, but are reacting to what you "typically" find in such papers. Whatever that is, it's definitely not "peer review", but you're bringing an appeal to authority on the basis that you are an experienced peer reviewer.

BTW, I think if you look at the actual paper, I don't think you'll find that you're that far away from what it's saying. Part of reforming decision making in these areas would definitely involve a careful look at the usefulness of and limitations to such engineering studies. They make some methodological points that I'm sure you'd likely have some interesting perspective on. Otherwise, you seem to have an axe to grind with Streetsblog which has prevented you from actually engaging with the actual argument.

The article is ostensibly about flawed traffic studies, with the apparent contention that reliance on these studies causes automobile infrastructure to be overbuilt. But they don't really back that up in any way and I haven't seen much in the way of this "problem" in real life.

I think the real point is made later in the piece:

"Nor, critically, do they stop to question whether all those new driving trips even should be accommodated — or whether the frustration of sitting in a traffic jam is just the push some drivers may need to walk, bike, or take the bus rather than drive."

Traffic studies may or may not be accurate, but the real push here is to reduce accommodations for automobiles. Build without concurrent infrastructure development and hope that will ultimately reduce the use of automobiles. And that, as others have noted, is a policy decision. The problem these advocates face isn't really the traffic studies but the desire of the populace to keep traffic moving at the same pace we now enjoy, if not better.

"IT'S ALL ABOUT THE MONEY BOYS". Elected officials have to decide what projects get funded. Funds are generally limited. The TS point out needs on the limited funds. Likewise, each elected officials wants their share. TS engineers try to point out the needs and to where the limited funds can do the most good. Most cycling and pedestrian projects are done with grants, (State and Federal). These alternative projects are pointed out in most TS as a requirement to get funding. Atlanta was deprived of some federal funding during the 1990's due to nonattainment on air quality. During this time, they became eligible for TEA (alternative), funding. Thats how the Silver Comet Trail, (60 miles), got built.
The good thing is more and more elected officials are becoming aware of alternative transportation needs.
Just an FYI.
Bruce E. Coyle, P.E.

I think engineers are good at developing answers to technical questions, but that defining what is "most good" really isn't a technical question. When it comes to transportation, it's a balancing of so many values that it's really about how you want your entire society constructed. Ultimately, I think the major problem with modeling traffic effects of hypothetical changes is that it really requires that the engineer predict the behavior of the masses. We're now in an era where the big empty parking lot surrounding the big empty mall is commonplace. Previous eras saw the devastation of inner city neighborhoods and city centers carved up by newly installed major traffic arteries inaccessible to anything other than motor vehicles.


I appreciate what you're saying here--there really is no substitute for policymakers and engineers broadening their perspective from the technical question of how many vehicles can you get through a limited space...

I think the opportunity might be there to change perspectives on this as expensive traffic-relieving program after expensive traffic-relieving program has been tried and failed. Boston traffic after the Big Dig, for example, may be worse than it's ever been before.

TSE in my area resulted in hatred changes. IE: The common people didnt want round abouts put in, yet there they are... not just one or two, but many. It removed a safer means for peds to cross, increased vehicle accidents, & has had no positive change in drive time.

Moving forward, I feel the primary objective for TSE is to maintain better traffic flow by encouraging bigger volumes of traffic to use highways, expressways, & major artery roads while discouraging traffic from using residential as a cut-thru, reduce speeds & volume for inner city/township areas that share a mixed zoned area containing residential & commercial buildings. Not likely to ever happen, at least in my lifetime.

They've installed a number of traffic circles in my area. As a driver, I like them but I'm in the minority. But pedestrian crossings at traffic circles really don't work. No one within the traffic circle wants to stop for peds as they fear they'll be rear ended. A valid concern. They would work better if moved further from the circle so traffic does not have to stop within the circle.

most of the circles are nearby schools, churches, or municipal buildings. So putting sidewalks in to avoid the circle would mean putting in traffic lights far out pre/post the circle to enable the peds to safely cross..... it's illogic, so that means it could happen!

The problem is that the studies measure current use of roads and ignore the factors involved. Add on street parking and motorists will tend to drive slower or look for alternate routes. Freeways can also become congested and result in motorists taking alternate routes on city streets.

The town where I attended university the engineer decided to speed up traffic and changed primary streets to one-way. The end result was traffic going too fast through the center of town and so the engineer put in new stop signs rather than go back to two-way traffic on the streets.

Traffic circles will handle more cars per hour than a 4 way stop. Pedestrian crossing at traffic circles needs to be at the neck, (before the circle), with sidewalks connections.

I learned how to drive roundabouts in Portugal this past October. I was very nervous at first but after Googling the rules, I think they make a lot of sense.

I'm also thinking a lot of collisions, which happen at intersections can be mitigated with roundabouts. Regardless of how busy or not it is, all drivers have to slow down and yield before they enter. That gives pedestrians and cyclists their safe time to cross. With traffic light intersections, too many motorists try to race the light as well as the pedestrians.

All studies have problems with preliminary bias on the part of the researchers, and more subtle bias that may creep in for other reasons.

On top of those---CoVid studies are gonna be the best example for the next couple centuries---are incorrect conclusions based upon statistical ignorance (or bias masquerading as ignorance).

Finally is the bias which is endemic to the "journalism" profession, where studies that reach conclusions which are not politically correct or popular (or both) are simpley suppressed or have clippings taken out of context.

"human piloted automobiles of low occupancy are an INCREDIBLY inefficient way to get people around, and i believe induced demand is very real, so we need to start with policies/goals that discourage the use of private automobiles to the extreme."

Buses ---the favorite hobby horse of the mass transit crowd--- with low occupancy are even more incredibly inefficient. Not only are they longer, wider, and higher than almost any vehicle on the road, they make frequent stops in the very lanes, and crossing the very lanes, that we cyclists seem to think should be sacrosanct for us.

I LOLed at how stupid that is/

buses are driven by professionals on fixed/planned routes. any decent transportation department can plan and avoid conflict between buses and cyclists, far, far better than private automobiles.

bus ridership would have to be INCREDIBLY low to make your size comparison even remotely relevant. a city bus takes the space of three stopped cars and two moving cars, more or less, and holds 50 or more people. as a cyclist, would you rather there be 40 cars on the road or one bus? 10 cars or one bus? 5 cars?

i’ve ridden many thousands of miles around urban buses and never once had one almost hit me or put me at risk, whereas this happens with cars fairly often.

presumably you want to make buses look bad and cars look good, but as threats to cyclists in typical urban environments, you are wrong.