Topics: Traffic Forecasting, Transportation Forecasting

Websites and Citations:

Atlanta Regional Commission Travel Demand Model Documentation

Theme Music: Five Star Fall, Mercurial Girl, Magnatune.com

Episode 45 – Traffic Forecasting

Hello and welcome to another episode of Talking Traffic. My name is Bill Ruhsam and I host this podcast and its sister website, talkingtraffic.org. Today is March 3 and this is episode 46 of Talking Traffic. Today’s episode topic is Traffic Forecasting.

I know what you’re thinking…Boooooorring. And I won’t lie, this is not the most engaging topic ever. Like, you’ll probably never sit down around a dining room table with friends, open a bottle of wine and say, “Let’s talk about the traffic analysis zones near home to better engage in the discussion of future land use with our local government!” Well, unless you hang out with a bunch of transportation planners. If that’s the case, bring more wine.

Before we get into some of the details, let me give you some definitions.

Traffic Forecasting, or Transportation Forecasting, according to the Wikitionary, “…is the process of estimating the number of vehicles or people that will use a specific transportation facility in the future.” In the general context, “vehicles” means literally any vehicle: Bikes, Autos, trucks, trains, ships, airplanes, etc. So transportation forecasting means any transportation. I’m going to concentrate on the specific example of forecasting that deals with roads and highways.

What this means on a day to day basis depends on what it’s being used for. I’ll give you some concrete examples to illustrate the differences.

Ok, your local municipality may have a problem with an intersection that is obviously related to the number of people turning right. The turning traffic is backing up into the through lane and causing a congestion problem. A solution is to make a turn lane, or extend the existing turn lane. But how long should that turn lane be? Nobody wants to spend more money than necessary, so you want to extend the turn lane as long as it needs to be, but no longer. And that “need” should extend into the future to meet the future traffic that will be coming through the intersection. So a traffic forecast here would simply be to predict the future number of vehicles using the intersection and turning right.

Now let’s say you’re Walmart and you want to install a new SuperDuperWalmartCenter. Obviously, as soon as you open you’ll have a direct impact on the street right next to the Walmart, but what about downstream at the next several signals, or the hypothetical interstate interchange that’s down that road? Now we’re talking about a whole system of roadways being affected by a large installation. That requires a much more detailed and in-depth analysis to forecast the traffic that will occur.

For a third example, let’s say you’re a metropolitan region. You need to plan for the future based on your best available information. You need to know where the traffic congestion will be worst 10, 20, 30 years from now. You have literally thousands of different variables and assumptions to incorporate into a forecast model that will look through its crystal ball out into the future. Based on that model, you’ll evaluate your transportation network and (hopefully) develop a plan to meet your future needs.

These are examples of the different scales of traffic forecasting. But they all generally use the same process. The process is called the four-step transportation forecasting process. Step one is Trip Generation, Step two is Trip Distribution, Step three is Mode Choice, and Step four is Assignment.

A “trip” is a journey from an origin to a destination by a particular vehicle type. These types are referred to as “modes”. So if you walk from your doorstep to the CVS, you’ve just made a trip by the pedestrian mode. The walk back is another trip by the pedestrian mode. If you drove, it would be a trip by an automobile mod[...]

Topics: Conspicuity, In Pavement Lighting, Stop Signs, NYC DeliverEASE, NJ Bridge Closure, Atlanta Traffic Snowpocalypse

Websites and Citations:

Chapter 2A of the Federal Manual on Uniform Traffic Control Devices

Redesigning the Stop Sign

NYC DeliverEASE Report

Waterfall Stop sign in Sydney

Theme Music: Five Star Fall, Mercurial Girl, Magnatune.com

Episode 44 – Grab Bag

Hello and welcome to another episode of Talking Traffic. My name is Bill Ruhsam and I host this podcast and it’s sister website, talkingtraffic.org. Today is February 2nd, 2014 and this is episode 44 of Talking Traffic.

Today we’re doing a grab bag of topics. There has been a bunch of stuff piling up for me to talk about but a lot of it has been of a short and sweet variety. Rather than do an individual podcast for each, which would last about 5 minutes, I decided to put together several into a miscellaneous topic episode. I’m going to talk about conspicuity, in-pavement lighting, the first stop signs, and the September 2013 New Jersey George Washington Bridge traffic fiasco.

…and the Atlanta Traffic Disaster of 2014. But that’s at the end and it will be off-script.

First off, lets talk about one of the words I learned solely as a result of me being a traffic engineer: Conspicuity.

Chapter 2A of the Federal Manual on Uniform Traffic Control Devices or MUTCD describes the requirements and applications when it comes to traffic signs. The MUTCD is described in more detail in episode 9 of Talking Traffic, but to sum up, it is the manual in the United States which sets out the requirements and guidelines for putting up traffic control devices such as signs and striping. Chapter 2A uses the term “conspicuity” 10 times and I love saying that word. Conspicurity. Conspicuity. It’s like some friendly disease. I’m sure I don’t have to tell you what it means, but just in case, Merriam Webster defines Conspicuity as the quality or state of being conspicuous. The MUTCD is solely concerned with making things more conspicuous, or in the language of chapter 2A-15, enhancing the conspicuity for standard signs.

You can do many things to enhance the conspicuousness of sigs including making them larger, putting up more than one of them (so-called double-indicating where you put an identical sign on the left hand side of the road), adding flags or flashing beacons, or my favorite, adding a strip of reflective sheeting to the sign post. You see this occasionally with stop signs, a long and tall strip of red reflective material that covers up the post. It does indeed make the sign more conspicuous leading to greater CONSPICUITY.

I love that word.

Another item that can lead to greater conspicuity is in-pavement lighting. In pavement lighting is just that, lights that are inserted into the pavement to, in the words of the MUTCD, “…warn road users that they are approaching a condition on or adjacent to the roadway that might not be readily apparent and might require the road users to slow down and/or come to a stop.”

Despite that very general statement, to my knowledge these in pavement lighting installations have been used universally at pedestrian crosswalks. They are set so that when a person presses the crosswalk button, they light up and begin to flash to alert approaching drivers that there’s a crosswalk ahead. Crosswalks are difficult to see from the perspective of the driver and these lights help their CONSPICUITY! Unfortunately, they’re also expensive and require maintenance. Any damage to the road surface almost invariably breaks the in pavement lighting power supply. There has to be a commitment on the part of the installing agency to maintain and repair them. The few before/after studies I’ve seen show that they are absolutely good things to install to increase the number of drives stopping for pedestrians, so that’s a good thing. Alas, they also seem to be falling out of favor amongst agencies.

Going off script for a moment…

The next item I’[...]

Topics: Roadway Safety Assessments a.k.a. Roadway Safety Audits

Websites and Citations:

Roadway Safety Audit website at the FHWA.

Theme Music: Five Star Fall, Mercurial Girl, Magnatune.com

Hello and welcome to another episode of Talking Traffic. My name is Bill Ruhsam and I host this podcast and it’s sister website, talkingtraffic.org. Today is January 5, 2014 and this is episode 43 of Talking Traffic. Today’s topic is Roadway Safety Assessments.

What is a roadway safety assessment, which are sometimes called Roadway Safety Audits? Well, it’s really exactly what it says. It’s an assessment of the safety of a segment of roadway. This segment might be a piece of a boulevard, or an intersection, or a tight curve in a rural location, or something else. A roadway safety assessment, which I will now call an RSA, is a process for looking at a possible safety issue and finding potential solutions that might address the problem.

Now, you have probably noticed that I’m using weasel words in that description. Words like “possible” and “potential” and “might”. There’s a reason for that, and it’s a reason that the RSA is designed to address. Here’s an anecdote from my personal experience:

There was an intersection in my county that happened to be within a roadway project I was the traffic engineer for. During our normal process of looking at all the intersections along the roadway, we analyzed that intersection for whether a traffic signal would be needed after the construction was complete. My conclusion was, No. No signal was needed. There wasn’t enough traffic, nor were there a number of crashes that could be addressed by a signal. Don’t forget, faithful listeners, that signals can *increase* the number of crashes that occur. That’s episode 12, where I also related this anecdote. Signals can increase the frequency of crashes, although they will generally decrease the *severity* of those crashes. However, if an intersection doesn’t *have* any severe crashes, than a new signal might increase the total number of crashes *and* injuries. That’s not a good situation. But, back to the intersection. When we went to the public meeting that was a part of the road project, I was asked at least four times when we were going to install a signal at that dangerous intersection. I kept answering no, we were not going to install a signal because it wasn’t warranted. Several attendees became a little short with me. After the meeting, I went back and did some more digging to see if there had been collisions out there that just hadn’t been reported, but to my knowledge, no additional crashes had occurred. This was an intersection that was perceived as dangerous, but wasn’t. Thusly why I’m using all these weasel words. Sometimes, when we’re looking for problems to solve, we have to be careful about requesting hot-spots from the public because we’ll get places like this one.

So an RSA is methodical look at a safety problem to determine what the root cause is, or if there are more than one, and how they can be addressed. Before I get much further along, you can stop right here and go to the Roadway Safety Audits website at the FHWA and read for yourself in a formal format exactly what they are. The website is http://safety.fhwa.dot.gov/rsa/ and contains all the details.

There are a couple components of the RSA that distinguish it from a safety evaluation that I might do, or your local town might do on a regular basis. The RSA brings together a multidisciplinary, independent team to do the work. By multidisciplinary, I mean you may have a traffic engineer and a roadway engineer, but you’ll also have a cop who works road crashes, and the local maintenance supervisor, and an EMS first responder. The exact composition of the RSA team isn’t set in stone, but it’s important that a mix of expertise, and especially expertise that is outside of the engineering realm be represented.

The other component of the team that is important is independence. Often, a[...]

Topics: Metacast. Talking Traffic is alive!

Topics: Interview with Steve Williams

Websites and Citations:

Georgia Road Geek Website

Theme Music: Five Star Fall, Mercurial Girl, Magnatune.com

Georgia Road Geek Facebook page

Hello and welcome to Talking Traffic. My name is Bill Ruhsam and I host this podcast and its sister website, Talking traffic.org. Today is Monday, February 27, 2012.

Today’s episode is an interview with Steve Williams. Steve is the man behind Georgia Road Geek .com, a website devoted to all things road geekery. He has videos and opinions and photos, and a link to his facebook page. It’s worth your time so go take a look.

This interview was recorded on September 20, 2011. We discuss Road Geeking, paper maps, High Occupancy Toll lanes, Public Private Partnerships, taxes and other things. It has been edited to remove some of rambling randomness that we discussed, although pieces of it I tagged onto the end of the podcast. I’ll alert you when the meat of the interview is over and when the rambling begins.

[interview not transcribed]

And that was our interview. You may have noticed me calling out “plug number four for the night” and wondered where two and three were? Those are contained in the edited ramble that is tacked onto the end of the podcast. If you want to hear about HAM radio, battlestar galactica and other associated geekery, keep listening after the end. If not, I hope you enjoyed this episode. Next time, we’ll have Steven Sheffield on to talk in a little more detail about High Occupancy Toll Lanes.

Oh, on a note of correction, during this interview I incorrectly stated that the Georgia I-85 HOT lane conversion was going to allow the HOV riders that had been using the lane to remain. That is incorrect. Previously you could use those lanes for free if you had two or more people in your vehicle. Now it is three or more.

If you have any questions or comments, please send an email to bill at talking traffic.org, and if you have a comment directly for Steve Williams, be sure to go to his blog and facebook page. Links will be on the show notes.

This podcast is released under a creative commons 3.0 attribution non commercial share alike license. Copy, paste, and alter to your hearts content, but don’t use this recording for commercial productions, and please give credit back to talking traffic and to Steve Williams.

The music you’ve heard has been courtesy of the background at Taco Mac, and by Five Star Fall. Five Star Fall can be found at magnatune.com. Taco Mac music can be found at taco mac. Obviously.

Until next time, have a great week.

Topics: Mast Arms, Strain Poles, Span Wires and other Signal Structures

Websites and Citations:

Theme Music: Five Star Fall, Mercurial Girl, Magnatune.com

Hello and welcome to another edition of talking traffic. My name is Bill Ruhsam and I host this podcast and its sister website, talking traffic .org. Today is Monday February 13, 2012. This is episode 41 and it is about mast arms, strain poles, span wires and other signal structures.

Have you ever thought much about how a traffic signal is erected and supported? I mean, we’ve got these green/yellow/red lights hanging in the air, being powered by electricity, but have you thought about what’s holding them up? I have, but then, that’s part of my job.

There are several considerations when choosing the infrastructure of your signal support. Firstly, and some might say most importantly, there is cost. Then there is size, and durability, maintainability, aesthetics, local weather conditions, and also the policy of the agency that is building the signal. This all gets roiled around in the cauldron of decision making which spits out an answer. These answers (at least in America) generally fall into two categories: Mast Arms or Span Wires.

A Mast Arm is a metal tube extending out over the intersection which is bolted onto a pole that sticks out of the ground. Generally, they are made of steel. In fact, now that I mention it, I don’t think I know any mast arm and pole assembly that is not steel. If you’ve ever seen one, let me know.

Span Wire assemblies start with poles sticking out of the ground and then steel wire is strung between them in a box, or other shape to support the signal heads. The poles that are used can be wooden, concrete, or steel. You will often see these sorts of poles sharing their span wire attachments with overhead utility lines like electrical service and cable TV. It makes sense to keep the number of poles in a particular location to the minimum number possible.

The signal lights ( we call them signal heads, and just to be even more pedantic, each individual green red or yellow light is called a signal section)… the signal lights are hung from the span wire or the mast arm along with any signs that might need to be up there. The wires that power the signals are routed through the mast arms and come out of holes at each signal location, or they’re fastened directly to the span wire and run along to each signal head.

The pros and cons of these two types of signal installations: As I said earlier, there are cost considerations, span wire will be cheaper and faster to install than mast arms. From a durability mast arms will do better than span wire, generally. Aesthetically, most people agree that mast arm installations look better than span wire, both from a professional perspective, and because you don’t have a bunch of wires that look ugly. On the maintenance side of things, it’s probably almost a wash because while you’ll have to do more maintenance to a span wire installation, if you need to move signal heads around for some reason, span wire is much easier. That leads us to local weather and local policy.

Policies are very different from place to place. Some agencies prefer to install mast arms because of the aesthesis and durability. Others prefer the cost and time savings over other factors. One thing that most look at, and if you’re in a southern coastal state in the U.S., you probably already know this, is wind speed. Span wire signals will blow around in high winds like nobody’s business and that can lead to damage to the signal. High wind-prone areas tend to go with mast arms as a matter of policy because they are sturdier. They also tend to hang their signal heads in a horizontal position, rather than vertically, to avoid excessive swaying in the wind.

There are other, more esoteric solutions to this problem of how to hang signals. If an intersection is exceptionally larg[...]

Topics: “Child at Play” Signs, Sharrows, and Jewish Crosswalks

Websites and Citations:

Effectiveness of “Children at Play” Warning Signs

Theme Music: Five Star Fall, Mercurial Girl, Magnatune.com

No Transcript this week

Topics: Trucks

Websites and Citations:

Theme Music: Five Star Fall, Mercurial Girl, Magnatune.com

Hello and welcome to another edition of Talking Traffic. My name is Bill Ruhsam and I host this podcast and its sister website, talking traffic dot org. Today is Monday, June 27, 2011. This is episode 39 of Talking traffic.

Today’s topic is about trucks. All kinds of trucks. But before I dive into the nebulous term that is “trucks” let me throw some engineer-speak at you.

When we are designing or analyzing roads, we talk about the “Design Vehicle”. The design vehicle is the largest type of vehicle that is most likely to use that road. For example, if I’m working on a residential subdivision, I dont’ need to design the road to allow a tractor-trailer to turn around in a cul-de-sac. No, a typical large vehilce for a subdivision would be a UPS or FedEx truck. Now, the occasional tractor trailer might come into that roadway, maybe a moving truck, but it only happens occasionally, and the inconvenience caused by having to back up a tractor-trailer to turn it around is small compared to the inconvenience of designing the subdivision to allow the truck to drive around as if it were an interstate.

It’s important to determine at teh very beginning what your design vehicle is because it will affect many different things in your roadway project.

Now, let’s talk about trucks. When I, as a traffic engineer say “truck”, I mean some specific types of vehicles. I’m not talking about pickups or SUVs or dooleys or anything that you migt see in a Ford commercial. I’m talking about larger vehicles that are intended to carry freight. These trucks break down into two cateogries. Single Unit trucks, and Multi Unit trucks.

Single Unit trucks are trucks that don’t articulate, that have a single frame to which the wheels are attached. UPS and FedEx trucks are good examples of these. dump trucks and garbage trucks and smaller moving trucks are all examples of the single unit truck.

Multi-unit trucks include the typical tractor-trailer combination that you see everywhere. These come in various sizes measured from the center of the front axle to the center of the rear most axle. So, when I’m throwing engineering speak at people. I would refer to the WB-62 design vehicle, which means a multi-unit tractor-trailer combination that has a 62 foot wheel base. This truck is actually about 69 feet from nose to tail. There are also the WB-40 and the WB-50 and the WB-65. For trivia purposes, the WB-65, which is 74 feet from nose to tail, is the vehicle used when designing interstaets and interstate ramp terminals.

The importance of the design vehicle becomes clear when you start putting together the design of intersections and sharp curves. Larger trucks need more room in order to make turns. The rear wheels of a truck–well, of any vehicle, really–will run to the inside of the front wheels. This wider path made during a turn is called overtracking, and its why you see large trucks swing out really wide when they’re making right angle turns at intersections. The distance and width needed to ensure that the rear wheels of the design vehicle stay off the edge of pavement, or out of the adjacent lanes, can add a lot of cost to a design project.

Next time you’re walking in an area that has curbs and you come to an intersection, look at the corners. Do you see tire tracks up against the curb faces? Do you see tire tracks on top of the curb, or on the sidewalk? Are the corners, maybe including the pedestrian ramps, broken and cracked? If any of these are true, it means most likely that truck drivers are running their rear wheels up and over the curbs when they’re trying to make turns. This could be becuase the driver isn’t very good, but more likely it’s because there’s not enough room for the trucks to clear when taki[...]

Topics: Rumble Strips

Websites and Citations:

Theme Music: Five Star Fall, Mercurial Girl, Magnatune.com

Hello and welcome to another edition of Talking Traffic. My name is Bill Ruhsam and I host this podcast and its sister website, talking traffic dot org. Today is Monday, June 13, 2011. This is episode 38 of Talking traffic and today I’ll be talking about those washboards of the road, Rumble Strips. Sometimes known as shoulder texturing, noise strips, rumble bars, or “Driving by Braile”. I’ll talk about what a rumble strip is and what it is for, plus their implications for safe driving

You will typically find a rumble strip along the edge of a high-speed roadway. These strips are designed to alert you when your tires roll over them by making a strong a vibration and noise. This tells you to that you are leaving your lane, on the way to a meeting with a tree, or possibly another car in a head-on wreck.

Rumble strips can be found on both your right side, on the edge of the road if you drive in the US, and on the left side, on the centerline. That second kind, on the left, is usually called a Centerline Rumble Strip, to distinguish it from Edgeline Rumble Strips.

These types of rumble strips are also referred to by pedantic engineers such as myself as Longitudinal rumble strips. In other words they are placed on the pavement *along* the roadway, rather than across it. You may also be familiar with rumble strips that *cross* the roadway. These are called transverse rumble strips and are used to alert you that you are approaching some sort of unusual location. Typically, I’ve seen them placed in rural areas before intersections that have had a high number of run-through-the-stop sign collisions. The rumble strip is to “wake you up” or just to alert your hazed and road-numbed brain that you need to stop.

Rumble strips are constructed in several different ways, depending on when they placed on the road. If they’re built when the pavement is built, then they can be cut, rolled, or pressed into the pavement as a part of the pavement laying process. On existing asphalt roads, they can be cut into the pavement. You can also use raised pavement markers or striping to make a rumble strip, although those are not as durable as ones that are built or cut into the pavement.

Do rumble strips work? Yes they do! Of course, you have to define what “work” means in order to make that statement.

Rumble strips are effective at preventing run off the road collisions if you drift to the right or head-on collisions if you drift to the left. However, they are dependent on having an adequate room to recover once that rumbling vibratory sound starts you back to awareness. If you are running off the road and immediately after you hit the rumble strip you’re on a soft shoulder or heading down an embankment into the weeds, that is not helpful. A wide safe shoulder is necessary to allow you time to correct and get back onto the roadway.

One dilemma that arises with rumble strips, however, is the concept of “migration”. “Migration” is the concept that rumble strips don’t stop the crash that would have been caused by an impaired or inattentive driver, rather it merely *migrates* it down the road to a point where the driver might cause a different sort of crash that could involve other vehicles. So instead of preventing the single-vehicle rollover or tree-strike, the rumble strip might cause a multi-vehicle collision of some other nature. There have been some studies that *suggest* this occurs, but to my knowledge there aren’t any that have concluded that it *does* to any degree of scientific certainty. It’s a difficult problem to address. How can you tell if that drunk driver who hit the family of five would have instead run off the road five miles back if the rumble striop hadn’t prevented it? the only way to really know is through stat[...]

Topics: Transportation Funding

Websites and Citations:

Episode 26 – Transportation funding in the United States.

Georgia House Bill 277

Theme Music: Five Star Fall, Mercurial Girl, Magnatune.com

Hello and welcome to another edition of Talking Traffic. My name is Bill Ruhsam and I host this podcast and its sister website, talking traffic dot org. Today is Monday, March 7, 2011. This is episode 37 of Talking traffic and today I’ll be talking about transportation funding. Specifically, transportation funding in Georgia.

Firstly, a warning and a reference. This episode is `about a bill that was signed into law last year here in the great state of Georgia USA. It’s complex, and convoluted and an example of why politics is so messy. If you’re interested in hard, fast, take-it-to-the-road facts about transportation, this is not your episode. Go. Run.

However, if you’re interested in what three years and a lot of political wrangling can produce and how it looks when the light of day shines on it, keep on! This is the episode for you. I encourage my Georgia listeners to stay the course because you will all be voting for or against this funding package on August 15th, 2012. Yes, 2012. We’ll cover that in a moment.

And, I mentioned that I’d give you a reference. Well, I’m referencing you back to Episode 26 of this very podcast: Transportation funding in the United States. That episode talks about the basics of how Americans fund their roads. *This* episode is getting into the specifics of how Georgians *may* decide to supplement their funding revenues. On with the show…

The first thing I’m going to do is summarize what House Bill 277 of 2010 enables for Georgia. Then I’ll discuss its specifics in general form. Lastly I’ll discuss its specifics. Seriously, it’s that complicated.

In short, House Bill 277, also called the Transportation Investment Act of 2010, enables voter referenda on a 1% sales tax for transportation funding. This sales tax would apply regionally, rather than statewide.  That’s the easy part. I just gave you the “in short”. Here’s the “in medium”.

This bill sets up what’s called a “regional roundtable” that will select from a set of projects that will be implemented with the funding acquired by the sales tax. There will be twelve roundtables, one for each region. These roundtables will comprise elected officials from the cities and counties and would have the discretion to select and approve the project list.  Once the project list is approved by the roundtables, it goes before the voters, again on August 15, 2012, who will vote the 1% sales tax up or down.

That was medium. The devil is in the details, however, and this law has a lot of details. If you want to stop now, I don’t blame you, because we’re about to go running down the rabbit hole.

Here are the details. From the signing of this bill by the Governor to the August 2012 vote, there are a lot of things that must be done. Some of which are already completed. After all, this bill was signed into law a year ago in 2010.

Step One: Step one is actually step zero because it wasn’t enacted by the new law, it’s something that has been in place. Step one is for the Planning Director of the state of Georgia to submit the Statewide Strategic Transportation Plan, which has to be approved by the Governor and the State Transportation Board.

Step two: The Planning Director submits a list of recommended criteria for selection of projects. The types of criteria that the director can recommend are spelled out by statute, but there is lots of wiggle room for specifics. The recommended criteria are sent to local planning organizations and governments within the twelve special districts or regions. The organizations and governments have a set amount of time to comment on the recommended criteria.

Step three: The regional [...]