Tag Archives: Safety
A friend sent me a link to a recent WRAL article posted yesterday about a fatal collision in Cary on Sunday, February 12th1. Tragically, both passengers in a left-turning vehicle died when the driver crossed the path of another vehicle. This is terrible and my condolences go out to those affected by the incident. I also feel for safety engineers everywhere who feel the emptiness of failure at each reported fatality2, especially the highway safety professionals who work in this jurisdiction. However, as an engineer and scientist it is of utmost importance to step back and remember a few things about working within the confines of the real world: with limited tax funds, systems are imperfect and not every collision is preventable.
Keeping these things in mind, how do traffic engineers decide if an intersection requires a traffic signal? We use a system of “warrants”, or reasons that warrant the installation of a control device. The Manual on Uniform Traffic Control Devices (MUTCD) lists nine signal warrants for varying reasons in Chapter 4C. A pdf of this manual can be found here. These reasons range from volume to school-zone related conditions and yes, even crash experience.4 Most generally, traffic signals are never installed without first qualifying for one or more warrants.
Why? In many cases a signal can make an intersection worse than it started! Traffic signals are often viewed in the public eye as a cure-all, when in fact they can have adverse affects on safety and efficiency: increased delay, increased traffic control disobedience, increased use of other routes such as neighborhoods (just to skip the light!), and others. The increased stops can also increase the number of rear-end collisions at the site as well.4 This has led to the installation of many lights that were never needed, at sites that may now be less safe, at the cost of a six figure installation. Thats right, your average 4-way simple traffic signal costs between $150,000-200,000. Plus continued maintenance from now until forever.
One of the biggest reasons that the public is so ill informed about the affects of traffic signals is the media, and we can see it in this article.2 It’s not necessarily their fault that the public demands stories that move the heart, either in tenderness, controversy, or horror. But people get so caught up in political partisan biases, that many forget how easy it is to be biased to the heart instead of the mind, allowing an element of “controversy” to develop conspiracy, scheme, even frustration in the reader. Lets take a moment to analyze some of the diction used in this article:
“hasn’t met the criteria for a traffic light, despite pleas from drivers and neighbors that the intersection is too dangerous”
I’d be pulling my hair out if there was any left to pull. On the logic side, uninformed readers could assume two very incorrect conclusions: drivers and neighbors always know a dangerous intersection when they see one3, and that pleas from drivers and neighbors warrant a traffic signal. But theres so much on the emotional side as well. Using the word “plea” to stab the hearts of our readers, the author has clearly set the tone of the entire article to:
“People have begged on hand and knee, offering to sacrifice their first born for just one, ONE traffic signal. The site would be safer, and this wouldn’t have happened”.
No wonder people think traffic signals are a cure-all! This conjecture could be patently false. For all we know without adequate evidence, adding a traffic signal could make this site WORSE. But not now. As uninformed citizens we now know that the evil city of Cary is denying us the promise of safety and security that only a traffic signal can bring.
“she attempted to turn left from West Chatham Street onto Cary Parkway and crossed into the path of a Dodge Avenger.”
This one earns the reporter kudos. Notice how quickly and easily the blame of the incident could have been shifted: 1) “she unwittingly pulled in front of traffic”, or 2) “the Dodge Avenger smashed into the side of her vehicle”. Unfortunately for the reader, we don’t know the exact cause of the collision. We may never know for sure. It could’ve easily been texting or another form of distracted driving. The author calls this collision “correctible”, though as a reader we are left unsure as to whether or not it is she or her interviewee that thinks it’s correctible and why. But by calling this collision “correctible”, the public will be wondering why correctible collisions are happening at all. And they should! But they are missing an important piece of the puzzle: some intersections are more correctible than others and warrant more immediate attention and funding, of which there is a finite amount of both.
“In addition to traffic volume and other criteria, to warrant a light an intersection would need to have had five crashes that would have likely been corrected by a traffic light in a single year.”
But I have to draw the line here, this is a complete falsehood and is misreported. Intersections do not require crashes for a traffic signal. In fact, new roads are constantly being built in conjuction with signals before they are even opened. But the remark is so instigating and confusing, it left one commenter with a terrible impression of traffic safety methods. If anything should make an engineer feel like a failure, it is the terrible miscommunication with the public that can lead to this:
Let me see if I have this right….The criteria for installing a traffic light requires multiple occurrences of either property damage, bodily harm, or loss of life. The wisdom of our city fathers leaves much to be desired. carrydoggymom, February 13, 2012 7:55 p.m
As much as a I try to avoid reading the comments section on a news website, it’s important from a public administration point-of-view to see how this fraction of the populace thinks. Some comments are enlightening, some are sad. This time, I was mostly surprised to see intelligent debate in the comments section. Mostly.
“I bet if it was the mayor’s family, there would be a light there tomorrow. What a load of bull!” bjandroxie88, February 13, 2012 7:42 p.m
Here is the advocation that, not only should tax dollars be spent willy-nilly by those in power when they find misfortune, but that politicians should make engineering decisions. There is a problem when the politically inclined try to mingle in the affairs of those who put safety first, a perfect reason why engineers should use MUTCD warrants instead of bending to political pressure from above.
“…If the vehicle was close enough to hit them, it was close enough to see and avoid.” pedsrndad, February 14, 2012 11:56 a.m
While my first instinct is inclined to agree, sight distance plays an important factor in intersection design, and it may need reinvestigation at this particular intersection. Though I imagine it was addressed and not seen as a big problem during the original design, factors such as reclassifying the speed-limit or increased volume year-to-year could play a part in changing the environment here.
I’ve driven the intersection myself, and especially during rush hour it can be difficult to turn left. The median supplies a little refuge, but not much. I glanced at the traffic volume maps, but without knowing more about peak hour data, it’s difficult to say exactly what warrants the intersection can qualify for. I’m surprised it doesn’t hit the peak-hour warrant, or even the school-crossing warrant with it’s proximity to Laurel Park Elementary. With the limited data I have on hand, I might recommend the following traffic studies to take another look at the signal warrants: sight distance study, spot speed study, and/or a volume study.5
If a light is installed in the near future, I hope it will be because it is warranted and that conditions have changed since the last inspection of the intersection. Not because of the ravings of uninformed watchers of the 6 o’clock news. We should all strive to be more cognizant of the impact media can have on the heart of the public, and how important good communication can be when working for the public sector. These efforts will make it easier to limit the affect of a tragic story in the news from opening our wallets too wide when there aren’t enough collisions to merit a new, expensive, and possibly ineffective traffic control device.
Wrap Up (Read: Important Conclusions)
By now you should have gathered the following:
- Traffic signals are not a cure-all; sometimes, when not really needed, they cause problems.
- We use Signal Warrants to come to justified conclusions, recommended by the MUTCD, on whether or not to add a traffic signal at an unsignalized intersection.
- MUTCD has 9 different signal warrants for varying reasons of safety.
- Intersections do not require collisions to warrant a traffic signal.
- “Pleas from drivers and neighbors” is not an MUTCD signal warrant.
- “The mayor found misfortune” is not an MUTCD signal warrant.
- Crashes and fatalities do not necessarily merit an MUTCD signal warrant.
References and Notes:
- Cary intersection doesn’t meet criteria for traffic light, WRAL, Monday, February 13th, 2012
- Mental Note: Prevented collisions never make the news. How could they?
- Mental Note: Drivers and neighbors are an invaluable resource when discussing what they think of an intersection. However, everyone’s seen a collision somewhere. This does not always, a “dangerous” location, make.
- Manual on Uniform Traffic Control Devices 2009, published by the Federal Highway Administration.
- As found in the Highway Safety Engineering Studies Procedural Guide, published by USDOT and FHWA 1991, commonly referred to as “The Parker Manual”.
The following is an email I sent to Wake County Representatives, concerning the issue of legislation-run engineering. If you can, write something similar RIGHT NOW to your representatives. A list of NC Representatives can be found here. Here is a list of NC Senators.
From: Mike Roselli
To: Jennifer.Weiss@ncleg.net, Paul.Stam@ncleg.net, Deborah.Ross@ncleg.net, Tom.Murry@ncleg.net, Grier.Martin@ncleg.net, Darren.Jackson@ncleg.net, Rosa.Gill@ncleg.net, Nelson.Dollar@ncleg.net, Marilyn.Avila@ncleg.net, Richard.Stevens@ncleg.net, Josh.Stein@ncleg.net, Neal.Hunt@ncleg.net, Dan.Blue@ncleg.net
Senators and Representatives,
I live in Wake County and I work in the engineering field. I’ve been made aware of H561, a bill to supersede engineering safety design decisions made by engineers at NCDOT. I urge you to NOT back this bill. It is not based on facts, research, or scientific credibility, but on fears of change. It has been well established in the engineering community that highway medians substantially increase driver safety and save many lives every year without impacting local businesses.
A research paper on this topic can be found here: http://blogs.newsobserver.com/sites/drupalblogs.newsobserver.com/files/docs/ncsu2009-12FinalReport.pdf
Over 30,000 people will die this year in the U.S. from motor vehicle collisions. We cannot set a precedence of State legislature overseeing every engineering decision made in the name of public safety. Do we remove stop signs when businesses ask? Do we remove bridge supports when someone finds them unappealing? That is, in essence, what some are suggesting: taking the complaints of the uneducated few and using these complaints to stifle progress in public safety and safety awareness at the cost of human lives.
I have a write up on my website with more details.
Thanks for everything you do,
Wake Co Resident
1. Source: List of Motor Vehicle Deaths by Year
Mike Roselli is a graduate of the NC State Civil Engineering Department. This writing reflects the views, opinions, and judgement of the author and does not necessarily reflect the views, opinions, or judgement of NC State University or NCDOT.
From: Mike Roselli To: Stephen.LaRoque@ncleg.net Sent: 5/11/2011 12:42pm
Dear Representative LaRoque,
I work for NCDOT and I have studied Highway Safety at NC State. Not only do I find Bill 561 a despicable act of politics, but I find it offensive for you to imply that you know more about the engineering of highways than the engineers at NCDOT. I urge you to reconsider your endorsement of this bill and read the facts. Here is a fantastic report on how medians do NOT affect local businesses, studied by researchers at NC State and UNC:
It will be a sad day when State engineers, who work tirelessly to provide life-saving solutions for collision problems, have to report to the state legislature about every median, stop sign, or other collision-reducing counter measure they want to install.
Today, the News and Observer reports that the State Senate will be voting on House Bill 561, to require NCDOT to remove a half mile of center median installed on new projects in Asheville, NC, “at a cost estimated by NCDOT at $797,500”, and to give the State legislature power over road design for other projects.
Other than ripping up a nearly completed project to nullify the design, the legislation would force DOT to change widening plans and forget other median installations planned on other routes. The fact that politicians, who know next to nothing about road design, can be influenced by their constituents to change engineered designs is unfathomably horrific.
Restricting left turns is good for safety. Median installations that require drivers to plan their left turns and u-turns at a limited number of intersections increase road safety by decreasing all sorts of collisions and allowing traffic to flow more smoothly. The decisions made in these designs were based on safety.
So who has a problem with this? Well, access restriction is seen by many locals as harmful to businesses, despite some studies showing evidence to the contrary. The latest is by a research team here at NC State and UNC, titled “Economic Effects of Access Management Techniques in North Carolina”. I’ve attached the study and you can download it here.
The study confirms that little to no evidence of economic problems was found after the installation of turn-restricting medians.
Additionally, it’s important to note that drivers are more aware of road safety than they think. And in fact, some drivers may be more inclined to use your business if they feel safer about entering and exiting the access to it. The Federal Highway Administration has a great write up on safe access and what it means for businesses. I’ve attached it and you can read it here.
Indeed, with enough fussing to the legislator whose campaign you backed, it seems businesses may be able to “buy” the road design they want for their businesses, regardless of safety concerns. Even in the face of state budgetary concerns, it doesn’t seem to bother Rep. Stephen A. LaRoque to use another million dollars to remove a brand new installation developed in the interest of public safety. What exactly seems to be going through his mind? This:
“The legislature should have the final say on projects like this before they go through.” -Rep. Stephen A. LaRoque
This is a problem. It is a sad day when engineers who make sound decisions based on data can have their life-saving designs overseen and rejected by
bought elected officials in the name of cheap tricks and politics.
Bottom line? Let engineers do their jobs. And write your representatives an email and tell them. I did.
Source: News & Observer
It seems the Senate has delayed voting on this issue for now. I’ll be posting more on this as it develops.