Episode 5 – A Grab Bag of Topics

Topics: Latent Demand, Funding, Anti-lock Brakes


Hello and welcome to Episode 5 of Talking Traffic, the podcast that brings simplicity to the field of Transportation. My name is Bill Ruhsam and I host this podcast and its attendant website, TalkingTraffic.org. Today is October 29th, 2007.

This episode is somewhat of a grab bag. I was perusing my notes, little jotted index cards where I keep ideas for future podcasts, and I came across several that were either hugely time consuming due to the amount of research or hugely tiny, not needing more than a few seconds worth of blurb. I didn’t want to devote the time necessary for the research on the big ones, and I also didn’t want to issue any podcasts less than a minute long. The solution: a compilation of smaller items, or a brief summary of larger items that can be covered quickly.

So! Today’s brief overview is: Latent Demand, Transportation Funding, and Antilock Brakes.

Latent demand is a term that isn’t used much outside the traffic engineering profession. You aren’t likely to hear it used in a news story or in common conversation about that road project down the street. Usually it is only used by people like me to defend a project that doesn’t appear to have any effect on the road congestion it was designed to fix. It is a description of what happens when you put so many vehicles on the road that you just can’t fit any more, yet more people still come.

What is Latent Demand? Well, for argument’s sake, let’s say that a given lane of traffic can handle 2,000 vehicles per hour (this is close to accurate). What happens if 4,000 vehicles want to use that lane? 2,000 of those vehicles will not be able to fit onto that lane during the hour and will have to wait until hour number two. That is latent demand. Keep in mind that for this exercise, the lane is 100% saturated. There is nothing we could do under this scenario to stuff through any more than the 2,000 vehicles. Now let’s imagine the same road is widened and now there are two lanes instead of one. The 4,000 vehicles can make it through during the first hour without any leftover vehicles, but both lanes are still 100% saturated. From the perspective of a driver in traffic, there’s been no improvement! The only thing that occurred was 8 months of frustrating construction, and now the two-lane road is still full! Why did they build it in the first place if it didn’t do any good?

I’m sure you see where I’m headed with this description. Latent demand makes it easy to see a project as having no effect, but in saturated conditions, a project will usually reduce the *time* of the congested period, which is useful from a commuting or air-quality perspective. Less time sitting in congestion means less air pollution.

On to my brief foray into Transportation Funding. This comes up because I have a quote from Commissioner Sam Olens, of Cobb County, Georgia. He said recently, “Some of us in public office want to move dirt and stop planning. The thing that is most lacking in our region is the ability to deliver on time. The bureaucratic delays are to the point that I’m turning down federal dollars.”

Commissioner Olens is referring in that quote to documentation necessary when you wish to have federal funds in a transportation project. First, let me make a quick description of how money ends up in transportation projects. In two words: Fuel Taxes. These are collected both at the federal and state levels (and sometimes locally). For example, in Georgia I pay 18.4 cents per gallon to the feds, and 7.5 cents per gallon plus an additional 4% sales tax to the state. The money that goes to the federal government comes back through federal matching dollars. However, in order to spend federal money, you also have to spend local money, which is where the “match” part of matching dollars comes in. Now the complexities emerge. When you want to spend the federal government’s money, they want a lot of oversight. This oversight is typically about twice as much paperwork and time as would occur if you were only spending state of local municipality money. Thus we hearken back to Commissioner Olens’ quote. “The bureaucratic delays are to the point that I’m turning down federal dollars.” I personally have experience where a project that could not move forward due to some history concerns was converted to a state-funds-only project and was built within a year. It would never have happened otherwise. And this wasn’t a project that needed slight of hand in order to run its way through a cemetery or Indian burial ground or historic church, etc. This was a ramshackle barn that no one wanted but qualified as potentially eligible for the national historic registry.

I know, Iknow, I’m betraying my disdain for the historic nature of rural Georgia. Well, you might have a point on certain occasions, but trust me, not that one. But back to my original point, which was Commissioner Olens’ quote and the ramifications of the funding issue.

Since Commissioner Olens’ said this, dirt *has* begun to move on several projects. And a few of those projects were stripped of their federal matching dollars in order to make them happen. He expresses the frustration of many people, not just politicians who want to show they are supporting good programs. When you are paying money into a special tax program such as the one funding these several projects, you want to see stuff happen. When it takes two years from the passing of the tax to the first shovel of dirt, it’s easy to believe that people (that would be me, in this story) are wasting your money. Quicker turnaround of projects is a necessity to keep public support.

Well, that was fun. And trust me, that *was* a very brief foray into funding. The ins and outs of transportation funding are complicated, to say the least.

The last thing I wanted to mention was Anti-Lock brakes. “What?” I hear you ask, do anti-lock brakes have to do with a traffic-themed podcast. Ah, bear with me, grasshopper.

If you listened to the last episode, number 4, about roundabouts, you heard me mention that blind pedestrians cross roads by the sound of vehicles. They listen for the traffic stream to flow and then cross with it. This is becoming a bit more problematic with electric vehicles that don’t make much noise. Now let’s imagine that a pedestrian or bicyclist (blind or non-blind, although I don’t want to meet the blind cyclist) is crossing a road when suddenly they hear the screeeeeeeeech! of a car slamming its brakes. I’m not going to quote odds on their likelihood of not being run over by the car which is panic stopping, but it’s got to be better than if they didn’t hear the screech.

Enter the anti-lock brake system. ABS brakes don’t lock up the tires, thus don’t cause the characteristic tire screech. Larry & James Bunker of Sunnyvale California want to fix that. They have a patent with the U.S. Patent and Trademark office for a device that would emit an artificial noise when certain braking thresholds are reached. So, if you stop hard, a screech will emerge even if you have ABS.

At the moment, James Bunker tells me that there are no systems yet implemented to achieve the screech effect, but he and his father, Larry, are still moving toward a deployed system.

All right! There we have three items for further discussion. Latent demand is the cause of much frustration to me, particularly at public information meetings, so if you’re ever at one of those, please don’t torture me when I try to explain it. Transportation funding is endlessly complicated, but I touched on a piece of it concerning the bureaucratic differences between state and federally funded projects. And anti lock brakes may be screeching in the future if Larry Bunker has his way.

Whether or not your ABS brakes screech, you’ve been listening to TalkingTraffic. If you have any comments, you can leave them on the show posting at talkingtraffic.org, or you can email me at Bill at TalkingTraffic.org. Suggestions for future topics are appreciated so I avoid boring the pants off of my audience.

This episode is released under a creative commons 3.0 attribution, non-commercial, no-derivatives license. Give it to your friends, but please don’t change it, or sell it, and make sure you leave a note that tells people where you got it. The music on this podcast is by Five Star Fall and can be found at magnatune.com

Enjoy your drives and remember to jump out of the way if you hear a screech.

US Patent #6,819,234, Vehicle braking system safety enhancements

Music: Five Star Fall

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