Highway design and traffic engineer
Expert class library · Transportation · Either side
A civil or traffic engineer who says whether a road, intersection, signal or work zone met design and traffic control standards, above all the Manual on Uniform Traffic Control Devices, and whether a different design would have prevented the crash. These cases turn as often on procedure as on method: courts police the line between disclosed standards opinions and undisclosed causation opinions, and appellate courts have reversed both an exclusion that left a plaintiff without any expert and an admission of a causation opinion sprung at trial.
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What this expert is retained to answer
- Which provision of the MUTCD or state standards does the expert rely on, and is it a mandatory standard, guidance or an option?
- Has the expert disclosed every opinion, including whether the design caused the crash, before trial?
- Does the opinion address what the responsible party actually controlled, such as the contractor's traffic control plan or the agency's signs?
- Is there evidence the driver perceived and responded to the signs or design at issue?
- Does government immunity or design immunity limit what the opinion can establish?
Methods
- MUTCD and state standard drawing compliance review
- Temporary traffic control (work zone) plan review
- Sight distance, signal timing and signage analysis
- Crash history and site inspection
- Comparison of the as-built condition with feasible alternatives
How the testimony is attacked
- Undisclosed causation opinions. An expert disclosed on traffic control standards may not add causation opinions at trial. In Arreguin-Leon v. Hadco Construction the Utah Supreme Court held it was harmful error to let a traffic control expert testify that the missing traffic control plan caused the accident, and ordered a new trial.
- Exclusion as too drastic a sanction. Courts weigh the importance of the expert before excluding for disclosure failures. In Lawes v. CSA Architects and Engineers the First Circuit reversed the exclusion of a pedestrian's only traffic engineering expert after a twelve-day Daubert hearing.
- The design did not affect the driver. Defendants argue the driver did not see, remember or rely on the signs, so their adequacy cannot have caused the crash, and pair the engineer with human factors evidence.
- Standards misread as mandates. The MUTCD distinguishes standards, guidance and options. Opinions that treat guidance as a requirement, or ignore engineering judgment the manual allows, are a common target.
- Control and duty. An engineer's opinion that a site was dangerous does not establish that the defendant controlled it. In Marin v. Department of Transportation summary judgment for the state was affirmed even after the court considered the traffic engineer's declaration.
What the public record shows
Courts have filed at least 250 opinions since 2015 that address this class of testimony under Daubert or Rule 702, as of October 4, 2026. Three that show how courts handle this class of testimony:
| Outcome | Case | Court | Year | Why |
|---|---|---|---|---|
| Excluded | Arreguin-Leon v. Hadco Construction, LLC2020 UT 59 | Utah | 2020 | Affirming the court of appeals, the Utah Supreme Court held the trial court abused its discretion by letting a traffic control expert, disclosed only on work zone standards, testify that the contractor's failure to implement a traffic control plan caused a highway worker's injuries, and remanded for a new trial because the error was harmful. |
| Exclusion reversed | Lawes v. CSA Architects and Engineers963 F.3d 72 | 1st Cir. | 2020 | The First Circuit reversed the exclusion of a pedestrian's only expert, a traffic engineer who relied on the MUTCD to criticize the pedestrian route through a construction zone, holding that the district court gave too little weight to the testimony's importance in excluding it for disclosure failures and as unreliable, and vacated judgment for the designer. |
| Exclusion reversed | Marin v. Department of TransportationNo. A161844 | Cal. Ct. App. | 2023 | The court held a blanket ruling sustaining 31 of 32 objections to a former state traffic engineer's declaration, without explanation, was an abuse of discretion and considered the declaration, but affirmed summary judgment because the evidence did not show the state retained and exercised control over the work zone where a worker was killed. |
Each case links to the free opinion text on CourtListener.
Under amended Rule 702
Since December 1, 2023, Rule 702 says expressly that the party offering an expert must show the court it is more likely than not that the testimony meets each requirement: that it rests on sufficient facts or data, uses reliable methods, and reflects a reliable application of those methods to the case. Questions about the basis of an opinion are no longer automatically matters of weight for the jury. For how the circuits have applied the amendment, see the Rule 702 tracker, which follows each court of appeals; for what that means for preparing or attacking this class of expert, see the guide on amended Rule 702.
Related classes
- Accident reconstructionist
- Human factors (driver perception and reaction) expert
- Workplace safety and OSHA compliance expert
Guides
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Last reviewed October 4, 2026. How this page is built: rulings are found by searching court opinions on CourtListener, and each one is read in the opinion before it is summarised here; outcomes are labelled by what the court did with the expert's testimony. No individual expert is named. This page summarises public decisions for orientation and is not legal advice; read the opinion before relying on any ruling.