Mike on Traffic

Traffic Signals 101

Here's a guest post from Max Moreland whose been working with me for about a year now.  Here is his take on the Traffic Signals 101 class he attended last week -

The course presented a broad view of traffic signals ranging in topics all the way from why they are installed to emergency vehicle preemption.  As an EIT working in the traffic engineering industry that has been out of school for about a year, I found this to be a useful course and would recommend it to those in a similar position to myself.

Since there was such a large range of topics presented in the course, there were plenty of things that I had already seen.  Some of these things were learned in school and other things I have picked up while working, but it was nice to see it all together in one course rather than in bits and pieces.

 Here are the top five things I learned at Traffic Signals 101:

1. Signal Agreements – Who pays for what?  Traffic signals are expensive, so it is important to know how cost, maintenance and operations are split up.
2. Signal Plans – If you are going to work with signals, you will need to know how to read a signal plan and a wiring diagram.  All those dots, lines and arrows are not just there to make everything look fancy and technical; they actually mean something!
3. Flashing Yellow Arrows – These are starting to pop up all over the place and learning their proper function is very useful.
4. Vehicle Detection – I remember talking about loop detectors in school, but I do not recall going into much detail on them.  Traffic Signals 101 gets into the different types of detection and detectors used in the field.
5. Emergency Vehicle Preemption (EVP) – The operation of EVP lights is more complex than I had previously thought.  There is more to it than just detecting an emergency vehicle in the area.

The course is only offered once a year, but you can check out the course workbook on MnDOT’s website. Here's a list of the topics covered:

1. Agreements
2. Field Components
3. Introduction to Plans
4. Cabinet
5. Controller Operations
6. Field Operations
7. Head/Loop Placement
8. Pedestrians
9. Advanced Warning
10. EVP and Railroads
11. Special Provisions
12. Maintenance

Crowdsourcing App for Better Fuel Efficiency

Researchers at MIT and Princeton have developed the Signal Guru app, which you can read about here.  Us traffic engineers are used to working on the supply side of the transportation capacity equation - adding more lanes or tweaking signal timings to improve traffic flow.  The Signal Guru allows drivers to work on the demand side of the equation.

Basically, if a lot of people are using the Signal Guru app, the computer that's receiving all of their GPS data can figure out the signal timing in the area.  This data is then fed back to the driver's smartphone to tell them if they should slow down or speed up to better sync with the signal timing plans.  Based on the initial trials done by the researchers, the drivers cut fuel consumption by 20% by driving per the Signal Guru directions.

Our traffic signals (at least in Minnesota) are very "wired."  Plus agencies are collecting a tremendous amount of traffic flow data with different types of traffic sensors.  You can pull up traffic flow maps with any smart phone to see current traffic conditions (the roads are typicaly coded green, yellow, or red - good to bad). 

If, and it's a big if, the researchers could tap this data stream to power the Signal Guru instead of relying solely on other Signal Guru users, a much more robust system could be built.  Anyone at Google listening?

Signal Knock-Down Solution - Adapt a Pole System

It's an unfortunate realty that folks drive off the road and knock down traffic signal poles.  One pedestal pole by my house has been knocked over twice in the last five years. 

James Knaub sent me a quick email letting me know about their new Adapt A Pole base system, which looks like a useful product to help technicians get a signal pole back in place quickly.  The plate gives flexibility so the bolt pattern on the replacement pole wouldn't have to match the bolt pattern on the foundation. 

Here's a quick demonstration video.  I'm curious to hear if anyone has used this product.

 

How to Forecast Hourly Volumes for Signal Warrant Analyses...

Tim Aziere, PE, PTOE from Baughman Company in Kansas emailed me this interesting question –

I am doing a signal warrant for a proposed mix-use development here in Wichita. The existing land use is a golf course and the proposed uses (10 of them) will generate over 43,000 veh/day. I have little doubt that a signal at the major entrance (two entrances proposed) will be warranted, but I am having trouble finding a credible way of distributing the daily traffic for the warrant analysis. Is there a program I am not aware of, or an industry standard I could use?

Signal Warrants Background

There's a technical process for analyzing traffic volumes at an intersection versus different criteria in the Manual on Uniform Traffic Control Devices to determine if a traffic signal is needed at an intersection (the criteria are called warrants to confuse the layman). "Engineering judgment" is sprinkled in to let us professional engineers interpret the tea leaves. 

Most of the criteria are based on the busiest eight hours of traffic volumes.  Traffic impact studies typically just forecast one or two peak hours.  The big question is how to estimate the eight busiest hours of traffic based on the peak hour forecasts.

My Response on How to Forecast Hourly Volumes for Signal Warrant Analyses

I've been in your situation half a dozen times.  I don’t know of a perfect, industry standard method.  The two routes I’ve taken:

1. Get a 24 hour count on each of the roads your studying with the data broken down hourly (or a nearby road if things aren’t built yet).  Assume the same hour by hour distribution will apply before and after the development.  So if your peak hour is from 5-6 pm; your 4-5 pm hour is probably 95% of the peak hour, 3-4 pm hour is probably 85% of the peak hour, 2-3 am is probably 5% of the peak hour, etc.  I assume you have p.m. peak hour turning movement forecasts that you can add up to give you the total flows into the intersection.  Apply the hourly ratios to distribute based off of the p.m. peak hour having a factor of 1.0.     
2. Go to NCHRP Report 365 – Travel Estimation Techniques for Urban Planning.  It has a series of tables in Chapter 8 that give hourly distribution factors for different types of land uses sliced by the population size of the overall metropolitan area.  You can use those factors to factor your peak hour forecasts into hour by hour forecasts.

Neither method accounts for an area that has highly directional patterns (residents go to work in the a.m. and come back in the p.m.) and I wouldn’t use either method for an intersection that was right on the bubble of meeting warrants.  But these are reasonable methods to back up your engineering judgment if you strongly believe a signal is needed.

Can Citizens Do A Traffic Study?

Kevin Lacy (Chief Traffic Engineer for the North Carolina DOT) doesn't think so according to the article Citizen Activist Grates on State Over Traffic Signals.  The DOT hired a consultant traffic engineer to perform a traffic signal justification study for two intersections in Raleigh, NC.  The consultant concluded traffic signals weren't needed as part of a road reconstruction project.  David Cox submitted his own traffic analysis on behalf of his home owners association that disagreed with the consultant traffic engineer's analysis and conclusions. 

I'm used to seeing citizen letters commenting on my traffic studies.  Some of them have even come with sketches for alternative roadway/traffic control designs.  In Minnesota, there are usually public hearings and citizen comments are asked for and considered in the design process.  Apparently Cox's analysis was too well done though.  Lacy submitted a complaint to the licensing board alleging Cox was practicing engineering without a license.

Cox was commenting on the design as a citizen.  As I understand it, the report never claimed to be prepared by a licensed engineer.  It will be interesting to see if the licensing board finds Cox was in fact practicing engineering without a license. 

Whether Cox has illegally practiced engineering or not, I wouldn't have lodged a complaint.  Ken Ashfeld, my boss when I was at the City of Maple Grove, beat into my head that the citizens are our true bosses and that we must respectfully listen to them.  Then we must logically respond with our engineering analysis and recommendation.

Cox's comments should have been reviewed the same way any other citizen comment should be reviewed - with respect and consideration.  It just so happened that Cox did a better job with his analysis than most citizens do (I'm guessing the citizens were persistent as well). 

Instead of going to the licensing board, a better response would have been a letter that either changed the decision about the signals or reaffirmed the decision in light of the new "evidence" submitted.  Then move on.

Signal Pushbutton Placement to Induce Behavior

Dan Lockton's website Design With Intent has an interesting series of "cards" pointing out different design principles.  Below is a snapshot of one related to traffic issues.  Traffic signal designers (me included) often design the pushbutton location as an after thought.  Per the slide below, it makes sense to put the buttons on the poles so the pedestrians need to look towards the oncoming traffic they'll be crossing.  I wonder what other subtle things we can do with our traffic control devices to induce the behaviors we want?

LED Signal Indications a Safety Hazard?

The April 2010 edition of the ITE Journal has an interesting article in it about LED traffic signal indications (titled Analyzing the Effects of LED Traffic Signals on Urban Intersection Safety).  The authors (Eustace, Griffin, & Hovey) found a 71% increase in crashes due to replacing incandescent light bulbs with LED indications.  I normally skim the ITE (Institute of Transportation Engineers) Journal, but this article caught my eye and I read the whole thing.

The authors studied the crashes at ten intersections in Middletown, Ohio where the incandescent bulbs were replaced with LED indications in 2003 and 2005.  There are two pages of statistical analysis related to the empirical Bayes method (assuming a negative binomial distribution) used.  This is a little over my head, so I'll trust the analysis is correct.

There is a relatively small sample size and there could be other factors contributing to the increased crash levels, but this is still an alarming study.  I hope FHWA and other agencies will study this further.  Traffic engineers assumed the brighter LED indications would be safer than incandescent bulbs(because of better visibility - the issue of snow sticking to them aside).  We need to go back to the drawing board if the current style of LED indications are causing a 71% increase in crashes.

Snow on LED Signal Indications - Low Tech Solution

My last post discussed snow covering LED lights.  Its a story that doesn't seem to want to go away. 

I came across a low tech solution sold by McCain (a large traffic signal supplier whose products are widely used in Minnesota).  Their Scoop Tunnel Visor has a beveled opening that provides air circulation around the LED lights which reduces snow build up.  They cost about $20 each (which isn't much of an upcharge if they are being put on new signals instead of the standard visor). 

The Colorado DOT has been using the scoop visor and seems to think they work.  According to CDOT spokeswoman Mindy Crane - "They've helped immensely in terms of keeping the snow off the traffic lights.  It's not high-tech and it's very economical."

Snow on Traffic Signals Lights

Most of you have probably heard about snow sticking to LED traffic signal lights, blocking the view and causing crashes.  The Associated Press put together an article on the topic this week.  It even quotes a few people from Minnesota.

The problem discussed in the article is slushy snow that falls in a windy storm can fly onto and then stick to the signal lights.  Old fashioned light bulbs were warm and would melt away the snow.  Most traffic signals have upgraded to using LED lights which allow the snow to stay because they aren't warm.  

There was a big push for LEDs about ten years ago because of the economic benefits (LEDs last longer and use less power - they're about three times more economical than incandescent lightbulbs).  I was a member of the local traffic signal committee and we discussed LED lights at length, including their inability to melt snow.  Another big issue was whether or not we need a $2000 battery backup system at every signal to keep the lights working when the power goes out (see MnDOT's dark signal report). Our conclusion after going through crash data was that there are few crashes caused by a traffic signal light that can't be seen.  Most people are more attentive in snowy or power outage situations and come to a voluntary stop when they are uncertain.

I would prefer to see the media focus on inattentive driving.  I think this is a much bigger safety issue (although its harder to get good photos for a news story).  Here are the crash risk results from a 2006 study by the Virginia Tech Transportation Institute (these results don't fully address the impacts of texting):

• Driving drowsy increases an individual’s near-crash or crash risk by four to six times.
• Engaging in secondary tasks that require multiple steps or eye glances away from the forward roadway increases risk by two to three times.
• Certain behaviors increased the risk of involvement in a near-crash or crash. Reaching for a moving objects increased risk nine times, looking at an external object 3.7 times,reading 3.4 times, applying makeup 3 times, and dialing a hand-held device 2.8 times.
• Talking or listening to a hand-held device increased risk by 1.3 times, but this result wasnot statistically different than normal driving.
• Looking away from the forward roadway for long glances at inopportune moments increase crash risk by two times that of an alert driver.

New Type of Red Light for Traffic Signals

Damjan Stankovic of relogik has come up with an innovative red light indication called the Eko.  It is a type of countdown red light for traffic signals (we already have numerical countdown indications for pedestrian lights).  The bars circling the light go dark as the wait at the red light gets shorter. 

The Eko could have two benefits -

(1) Less Stress - Drivers would see that they are getting closer to a green light.  It's the same concept used by computers with the spinning hour glass when you are opening a file or program.

(2) Environmentally Friendly - There are some folks out there who turn off their engine at a red light to save gas.  The Eko would let those people know when to turn their car back on.  Maybe this would encourage more people to use this gas saving/pollution reducing technique.