Traffic Impact Study Process – Part 3: Document Existing Conditions

Cover art for the Traffic Study Manual. Blue background with pictures of stop lights, construction vehicles, and a four leg intersection

Mike Spack and Bryant Ficek have literally written a book about Traffic Impact Studies and the process from authorization to final study. We present the information we wish we had when starting our careers and hopefully have tips and refreshers that even experienced traffic engineers will find useful. This series presents the basic steps of completing a Traffic Impact Study from their book. See the early posts here.

More than likely, the area of your study is not next to your home or office and you may have little to no knowledge about the transportation system around the site. Not to worry as this task helps you gain that base understanding. The purpose of this task is to help you gain an understanding of the area around the proposed development, both its land uses and traffic operations.

Online Research

Most public agencies use the internet to post a wealth of information about themselves, including relevant data for your traffic study. You can use this information to understand better what they see as the existing and future characteristics of the site. Here’s what we look for:

  • Transportation plans
  • Traffic study policies
  • Other nearby development plans
  • Capital improvement plans
  • Traffic impact fee schedule

The first place to start your online research is the planning department page of the local government (city/town/village) website. You’re trying to find their transportation plan if they have one. The transportation plan is usually a section of the local agency’s overall comprehensive plan and describes the vision for their transportation network. It could be listed under the public works or engineering sections of the website if it isn’t under the planning department. The transportation plan is usually a PDF file that can be saved to your network or bookmark it for easy access later.

While you’re in the local agency’s comprehensive plan, you can also gather land planning information for your development. Some relevant questions to ask include:

  • What is the current land use of the parcel?
  • Is the land use proposed to change in the plan?
  • What is the current and proposed zoning of the parcel?
  • What is the land use and zoning of the adjacent parcels? Some clients/public agencies like to have this background information in their traffic studies.

The developer may have provided answers to some or all of these questions, but it never hurts to verify the data.

As you are looking at the local agency’s website, search for agency policies related to traffic impact studies. It’s rare in our experience, but some cities do have explicit policies providing the exact detail of the study needs and process. They may be detailed enough to give you a full outline for the study along with what to include in each section and what graphics are required.

Sometimes, the local agency’s policies are part of their ordinances, and almost all have their ordinances posted. You should scan through them to see if there is anything relevant to how closely intersections can be spaced or how much vehicle delay is considered unacceptable. If you’ve never searched through ordinances and codes, this may seem like a daunting task at first and will take some time. However, after a couple of projects, you will recognize the different chapters or words to search for, reducing the time you need to sift through the information.

The local agency’s planning page may also list nearby developments either under construction or in the approval process. They may even include traffic studies prepared for those specific developments. Prior traffic studies are always useful for seeing the types of studies the agency typically approves and what kinds of assumptions those studies make. If the assumptions remain reasonable (i.e., it’s a recent study, no major infrastructure projects since the study, etc.), it’s good for your study to make assumptions consistent with those of previous traffic studies.

Most local agencies also list the construction projects scheduled for the next five years, often labeled the Capital Improvement Plan. See if any construction projects are affecting your study area. It’s also wise to let your client know if the road in front of their development will be under major reconstruction the year after their project opens. This kind of information may cause a developer to delay an opening date for a commercial/retail project and or impact your analysis data collection (we’ll get to that in the next Part 4).

Many government agencies around the Country charge traffic impact fees for new developments. These fees are charged for future transportation improvements and are typically assessed based on a proportion of traffic the development will generate compared to the total traffic on the facility. Traffic impact fees are not allowed in Minnesota, but they’re widely used in states such as Florida and California.

You may need to devote a whole section of your study to calculating impact fees. Each jurisdiction should provide detailed formulas for you to use in determining any traffic impact fees. In addition to the local agency’s website, a good clearinghouse is located at

Now it’s time to move up the chain of government agencies to the county and eventually the state. If one of the site’s driveways is proposed on a state or county road, they will have jurisdiction over your traffic study. As you did at the local agency, look for:

  • Traffic study policies
    • Traffic study standards
  • Transportation plans
    • Capital improvement plans
    • Traffic volume data
    • Historical daily traffic volumes
    • Peak hour turning movement volumes
    • Crash data

Through the property records section of the county’s website, you can typically find parcel information, including public right-of-way widths. This right-of-way information may be useful if you end up recommending road or intersection widening as part of your traffic study.

Lastly, if your study area is served by bus or rail transit service go to the transit operator’s website to get routes and schedules. You may need to account for transit operations in your capacity analyses.

Existing Conditions from Aerials

As part of your online research, we also recommend you start with your favorite aerial online site or software, such as MapQuestTM, Google EarthTM, BingTM or Google Street View. Draw a quick and dirty sketch of each study intersection based on the aerial with the following details:

  • Exclusive left or right turn lanes – measure their storage lengths on the aerial and
    include them on the sketch
  • Through lanes and/or shared lanes if turn lanes aren’t provided
  • Traffic control – stop signs, traffic signals or roundabouts
  • Medians
  • Shoulders
  • Sidewalks
  • On-street bike lanes
  • Nearby parking lots
  • On-street parking
  • Street names

Also, print out a street map of the study area. We like to make field notes on maps. Ensure the map is zoomed in enough so you can make notes of things between your study intersections. We find we’re more accurate correcting our sketches in the field than trying to create originals while we’re on the side of the road. Something usually gets missed if we skip this first task in the office.

Field Visit

You may be asking yourself why you even need to go out in the field when everything is right there on the online aerial. First, because the aerials aren’t always right. Imagine the disaster awaiting the engineer who turns in a whole traffic study based on the obsolete road network. The study would have had zero credibility, and the client may have some choice words to say to the engineer. The second reason to go out to the site is there are frequently many important details you can’t always see on an aerial.

Ideally, the field visit should occur before your traffic counts are taken. As we mentioned earlier, details from an aerial can be wrong. The field visit will help you figure out if the data collection plan needs to change as well as to determine good parking spots for your data collectors.

In our office, the field visit is usually combined with the data collection part of the project. Here’s our approach to the fieldwork and ensuring the existing study characteristics are verified:

  1. The engineer views the study intersections and roadways online, printing a close-up of each one.
  2. The engineer lists the items to verify in the field, such as parking restrictions, etc., and the initial location for the field equipment.
  3. The field technician, as part of the data collection work, verifies the study intersection and roadway information per the engineer’s information.
  4. The engineer completes a secondary review and verification using the videos from the data collection.

We discussed the online work in the prior section. By printing a one-page sheet for each intersection, notes can be added for reminders about things to look for as well as having space for other notes once in the field. We have a standard list of items to examine in the field, which can be copied and pasted onto to each sheet, including:

  • Transit stop locations
  • Traffic signal operations (protected left turn phasing is shown on the left, protected/ permitted left turn phasing is shown on the right)
  • No turn on red restrictions
  • Parking restrictions
  • Posted speed limits
  • Non-ADA compliant signal push-buttons or pedestrian ramps
  • Excessive grades or slopes (that either affect traffic operations, like the steep hills in Duluth, Minnesota that get iced over in the winter, or making widening a road difficult)
  • Vegetation, objects, or buildings on the intersection corners that block sight lines

Once the field technician is out at the site, we encourage taking plenty of pictures. Smartphones are a convenient and amazing tool for this task because they produce really good photos. Get one photo of each approach at each study intersection. Be certain to keep a log of the photos so you can identify them back in the office. Taking pictures has saved us more than one field visit. It’s amazing how often one little detail is usually missed while you’re doing your field check, but photos won’t help you find that detail if you can’t identify their location.

Another on-site option is a dash-mounted or another type of video camera recording both the study site and your dictation simultaneously (smartphones could again help here). You have less organizing to do if you go with video, but it’s easy to get lazy and miss specific signs or other data if you’re not careful. Keep in mind that video is always recording sounds, so please watch the language. Do feel free to sing along with your favorite song though. Anyone reviewing the video will find their day instantly brightened by that.

While you’re verifying the accuracy of the hand sketches, be aware of other things that could affect traffic in your study area, such as:

  • Large parking lots that could affect the balance of traffic between study intersections
  • Large pedestrian generators, such as schools
  • Road construction
  • Developments under construction

If the technician is in the field during a peak hour, they can make some general observations of traffic flow. Our process has the engineer completing a review of operations using the captured videos from the data collection. This review provides the engineer a feel of operations to compare against when using computer analysis and allows them to confidently state they have observed operations. As we review the operations, here are some of the issues to consider/look for:

  • Do shoulders get used by cars as separate right turn lanes or bypass lanes?
  • Do the traffic signals along a corridor seem to be coordinated, so through traffic moves down the corridor smoothly?
  • What are the signal cycle lengths? Bring a stopwatch or use your phone to spot check the time it takes for the signal timing to rotate all the way through its cycle. Be sure to measure several cycles as they can vary.
  • Are there any queues backing up from turn lanes into the through lane or do queues extend back from one intersection blocking the upstream intersection?
  • Is it hard to turn onto a major street from a cross-street with a stop sign?
  • Do your expected travel pattern and routes to and from the proposed site correspond to the major traffic flow you’re watching?

These firsthand observations could save your reputation in a public hearing. Citizens regularly grill us about how traffic currently operates at a specific intersection. If we’ve been on-site or specifically watch operations during rush hour, we can honestly respond with our impression of volumes and traffic patterns. We can further explain how we incorporated those observations in our analysis.

Documenting existing conditions is necessary to provide the base information in computer models and other aspects of a typical traffic impact study. More importantly, this step should be viewed as an opportunity to fully understand how traffic operates today.

This is a multipart series. Check out the other articles in this series.

Bryant Ficke Bio