June 13


Expert Witness Do’s and Don’ts

By Mike Spack

June 13, 2017

COUNTcam, expert witness, Technical Expert Witness, testify, Tort law

By Mike Spack, PE, PTOE

Tort law in Minnesota regarding the installation of medians to limit traffic movements at driveways has been in place and tested since the 1960s.  It is very clear that road authorities have the right to place medians on roads to limit access to cross streets or driveways so long as access is available in one direction.  I routinely get called by property owners and their lawyers that want to maintain their access and contest this type of project.  However, unless property along with the access is being taken from the land owner, or unless agreements regarding access to the side street are in place allowing access to the major road, I regretfully tell them there’s nothing I can do to help them (and in the majority of these cases the median closure makes sense from a traffic mobility perspective).

A few months ago I was hired in one of these cases, but it had a twist.  The service station that I represented had access from a side street that had signalized control with the Major route.  The median was put in eliminating the signal and limiting access the side street to ¾ access, thus eliminating access to the station from one direction and access from the station in two directions.  The lawyer found case law supporting the case that the service station was entitled to compensation as they had a right to expect access to the major road via the side street.

I was brought in early on the project and was able to acquire traffic counts in the before conditions.  I counted the cars coming in/out of the site over 24 hours (thanks to our COUNTcam video systems) in the before conditions and again in the after conditions, and compared the driveway counts.  Turns out the site traffic dropped by approximately 20%.  This was a technically straightforward, factual study.  My client then had me present my study at the commissioners hearing.  I routinely present as an expert witness in a “court hearing”, and here’s my top 10 do’s/dont’s for testifying:

  1. DO give your credentials and elaborate on your background.
  2. DO tell the truth.  Stick to the facts.
  3. DON’T speculate.  Answer “I don’t know” when you don’t know.
  4. DON’T volunteer information, let your attorney draw the information out that he/she needs.
  5. DO stop talking if interrupted.
  6. DON’T use jargon.
  7. DO take your time to think.  Make sure the lawyer is done with their question.
  8. DO answer with a yes or no when asked a yes or no question, particularly on cross examination– if your attorney needs more information he will get it on redirect.
  9. DON’T answer questions you don’t understand.  Ask for clarification.
  10. DO cite sources when describing technical analysis and why the source is relevant.

Have you been called to be an expert witness? If so, I would love to hear your thoughts on your experience. Add your comment below.


  • Good points, Mike!
    My comment involved a situation in a western state where a grass- cutting mower pulled onto travel lanes from a median area to cross a narrow bridge. This occurred on an interstate highway posted at 75mph out in the middle of nowhere, and resulted in a collision with a Greyhound bus with several fatalities and major inhjuries. The questions were simple ones. Did the state have traffic control guidelines; were these guidelines consistent with national standards; and did the state follow those guidelines. YES was the response to all three questions, but there was more to the traffic control story than the court proceedings allowed. Greyhound paid, the state did not.

  • To add or elaborate on your do’s and don’ts;
    There are only five (5) answers to an asked question
    1 “yes”, (and shut up)
    2 “no”, (ditto)
    3 “I don’t know”, (ditto)
    4 ” I don’t recall”, (ditto)
    5 As short/concise answer as is reasonable

    Don’t help the attorney ask his question (they’re not that stupid, just fishing)

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    Mike Spack

    My mission is to help traffic engineers, transportation planners, and other transportation professionals improve our world.

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