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Thread: Traffic count meanings

  1. #1
    Cyburbian Streck's avatar
    Jun 2002
    Southeast US

    Traffic count meanings

    I am not an engineer or a Planner, but am on the Planning Commission.

    What do the daily traffic counts tell us for the various road types, and what do we do with the information?

    What is the proper way to assess the traffic counts we get? Do we count the traffic for a whole day and multiply accordingly?

    Do we count for a whole day when our problems are only at peak periods such as at rush hours?

    How does daily traffic count account for traffic jams?

    If we have traffic jams, doesn't that reduce the daily count and make it appear that we have no problem?

  2. #2
    Feb 2013
    The Midwest, God's gift to Planet Earth
    Planner here who helps the City Traffic Engineer review Transportation Impact Studies for new development proposed at Planning Commission.

    Traffic Counts tell us the baseline, or existing conditions of a roadway. We request our studies to have multi-modal counts and turning movements (cars, trucks, bikes, peds). Usually these are performed at rush hour, or other identified peak times in order to capture the 'worst case scenario' (which isn't always the best way of doing things, but anywhoo).

    Jams, or congestion is measured through Queuing Analysis (how many cars queue up, stalled and waiting at a light) and vehicular Level of Service (an A-F grade given to a street to measure its efficiency of traffic flow). Nowadays, vehicular level of service is considered potentially anti-pedestrian, so best practice is to move towards Multi-Modal Level of Service, which many cities have either adopted or are looking to adopt.

    All of this information is combined into a Transportation Impact Study/Assessment (TIS/TIA) report, and then based on how many trips are projected to occur from the new development, the report will advise mitigations. This could include optimizing the signal timings, adding pedestrian crossings on existing signals, adding or subtracting turn lanes, adding stop signs and driveways, adding or moving a crosswalk, adding or removing on-street parking to accommodate loading for the new development, or at the high end, adding a new traffic signal. Some cities go an extra step and assess multi-modal impact fees on developers - for example, if the study shows high pedestrian volumes, then the development might have to increase their sidewalk width. You do have to be careful because while there are some good consultants who write these reports, there are also some bad ones who will just write whatever the developer says to get him/her out of making any meaningful improvements. Remember that the consultant is hired by the developer. That's why it's important that your municipality's transportation staff (both traffic engineer and transportation planner) thoroughly review each study. Unfortunately, sometimes this takes multiple back and forths, resulting in a review time of a multiple months depending on how much new development your city is getting and what the staff capacity is like in your Zoning or Public Works departments.

    Here is a great introduction from my alma mater on counting traffic! http://www.ctre.iastate.edu/pubs/tra...fficcounts.pdf

    Hope that helps! Keep in mind that there are two types of counts/studies - studies done for new development which usually go through Planning Commission, and studies/counts done in-house (or more likely, bid out to an on-call engineering consultant) for City capital projects (ex: changing a street to accommodate a bike lane).

    I'm not sure about your last question.

  3. #3
    Cyburbian dvdneal's avatar
    Jan 2009
    Remote command post at local bar
    I tend to use it like any statistics. Without something to compare it with it's worthless. I like to use total (all day) counts. How will this project impact the total traffic on the road, but I don't have to deal with a lot of congestion traffic. If I did I might go for peak hour counts. It's also helpful to get an understanding of the entire report. Total volume, peak volume, level of service at lights, how drivers will react to congestion. Will it be shifted to other roads? Will transit cut it down? Will this new project become a destination increasing traffic? The questions are endless. Enough rambling and back to the comparison thing. I like to compare the existing number to the new number and then show my commissioners a well known street with the new number. Then I can say traffic will increase from what we have on 1st street to what we have on 2nd street and they all get a mental picture of what that traffic is like. If you're dealing with a lot of congestion I would start asking about the level of service at the light along with the peak hour numbers. If it helps, think of traffic like water. It will usually flow straight until something backs it up (a stop light). When that happens all the drops of water back up until the light changes and they all rush through. Traffic counts don't really show congestion, but they aren't lowered because of it. What usually happens is that the congestion acts like a dam to the water and it starts spilling into other streets looking for the path of least resistance. What I would recommend, have someone get you a traffic count map of the city. Just a regular total day count. Look at the counts for familiar roads where congestion happens, where there is no congestion, and where the roads have normal traffic. Also take note of how many lanes on are on the road. Then when you're given a traffic count think back to those roads and think about the differences between the street you saw and the street you're considering.
    I don't pretend to understand Brannigan's Law. I merely enforce it.

  4. #4
    Cyburbian Streck's avatar
    Jun 2002
    Southeast US
    Thanks aklshali2000 and dvdneal.

    I came across a county traffic study on the net that includes part of our city, and it does a good job of explaining some basics, and your responses help fill in the gaps.

    It is available to browse on the net complete with charts, diagrams, pictures, ratings, and summaries on major roads and intersections along with recommendations of priority of need.

    This helps me a lot, and I will browse it for awhile so that I can better understand it.

  5. #5
    Cyburbian Veloise's avatar
    May 2004
    Grand Rapids, Michigan (Detroit ex-pat since 2004)
    As the admin for the Michigan ghostbikes FB page, I use traffic counts to discuss bicycle safety measures. A big part of what I do involves refuting the rumors and fear presented by folks in the news comment sections. For instance, any bicycle piece will contain comments like these:

    Really irrevalant who has the right of way and who does not.....the simple fact is a bicycle will always lose in a confrontation with a car or truck.... Simple common sense regardless of rules, regulations, and laws, dictates the majority of defensive driving and responsibility has to be on the bicyclist. ....separate bike paths should really be the goal .

    First of all some of the folks making intelligent comments here about watching out for their own butts instead of sacrificing their health and lives for the Bike Mafia are riders. Getting bikes OFF the roads and away from traffic should be the goal of bike organizations. Forcing bike lanes onto busy roads is a toxic mix designed for fatal consequences because accidents are going to happen and the bicyclists are going to lose every time no matter who is at fault.

    Looking at the picture I don't see a shoulder on this stretch of road.
    I am always amazed when I see bikers riding on roads like this. It takes an amazing amount of faith to believe that you can expect to arrive at your destination safely with all the drivers we have today who distracted by cell phones and text messages and who knows what else.
    I am well aware that bikers have the "right" to ride on the highway but insisting on taking advantage of that "right" strikes me as somewhat fool-hardy as this story illustrates and is the very possible outcome.
    I regularly ride on Pettis from Knapp to Fulton. There is a very adequate well marked shoulder on this stretch of road. Being 74 years old, I usually ride on the wrong side of the road against the traffic so I can see any distracted drivers before they hit me. I get yelled at for being on the "wrong" side of the road by "professional" bikers occasionally and I yell back at them that that's the way I was taught to ride back in the dark ages when I learned to ride a bike so get over it.

    For this incident (8:15 pm on a Wednesday in August), I provided the traffic count map (about three cars per minute) and an aerial.

    Click image for larger version

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    Click image for larger version

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    The hit-skip driver was apprehended when his (former) employer, a landscaping company, discovered his wrecked company vehicle the next morning. Driver has a long rap sheet including prison stints; hasn't held a valid driver's license for most of two decades. The crash has nothing to do with ADT or roadway design.

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