What 393.78 means in plain language
FMCSR 393.78 targets one specific condition: a windshield that has deteriorated to the point where it compromises what the driver can see while operating the vehicle. That means cracks, chips, discoloration, delamination, or any other physical defect that blocks, distorts, or significantly reduces the driver's forward field of vision.
The regulation does not require a perfect windshield. Minor chips well outside the critical viewing area are a different matter entirely. What gets you cited is damage that a reasonable inspector can point to and say it materially limits what the driver sees — a large crack splitting the driver's sightline, a spider-web fracture across the center of the glass, or severe pitting that scatters light into the driver's eyes on night runs or in direct sun.
Practically speaking, if you can draw a straight line from the defect to a situation where you might miss a hazard in the road ahead, an inspector likely will too. This is a condition code, not a paperwork violation — and it lives inside BASIC 5, the Vehicle Maintenance BASIC that weighs directly against your carrier's CSA profile.
What our enforcement data actually shows
Across our 13 million+ inspection records, 393.78 has accumulated 157,894 all-time citations, making it the 10th most-cited code out of 3,036 FMCSR codes tracked in our database. That is not a fringe infraction — it is one of the most routinely written violations on American highways.
In the last 12 months alone, our inspection records show 44,990 citations issued under this code. Zoom in further and the last 90 days produced 9,334 citations, confirming that enforcement volume is not declining. Looking at the monthly trend, citations climbed from 3,901 in May 2025 to a peak of 4,373 in October 2025, then settled into a consistent band of roughly 3,600 to 4,100 per month through early 2026.
Here is the number that should actually reassure you if you were just cited: the all-time out-of-service rate for 393.78 is 0.3%. Out of 157,894 total citations, only 402 resulted in a vehicle being placed out of service. The remaining 157,492 inspections ended with the driver back on the road. Compare that to the all-FMCSR average OOS rate of 31.4% across all codes in our database — 393.78 sits more than 31 percentage points below that average. This code is flagged frequently but almost never grounds a truck.
That said, 393.78 carries a CSA severity weight of 4, which means every citation does add points to your carrier's Vehicle Maintenance BASIC score, even without an OOS event. Accumulate enough of them across a fleet and the FMCSA will notice.
Who gets cited most
Looking at the last 180 days of our inspection data, Texas leads all states by a significant margin with 16,748 citations — more than 44 times the count in the next highest state. That concentration reflects both Texas's high commercial vehicle traffic volume and the density of inspection activity along major freight corridors near the southern border. Illinois recorded 291 citations with a notably higher OOS rate of 2.4%, compared to Texas at 0.0% and New Jersey at 311 citations and 0.0% OOS. While 2.4% is still far below the national FMCSR average, Illinois inspectors appear more willing to escalate a windshield defect to an OOS determination than their counterparts in other high-volume states.
Our data shows fleets such as AUTOTRANSPORTE CA-RI SA DE CV (USDOT 1759246) with 337 all-time citations and JESUS MA VALDEZ GARCIA (USDOT 2534784) with 276 citations appear at the top of the carrier citation list. Both are cross-border operations where vehicle condition checks at ports of entry and weigh stations tend to be especially thorough.
How severe is this compared to similar codes
Within the Vehicle Maintenance category, 393.78 holds its own in raw citation volume but looks relatively low-risk when you examine OOS outcomes against peer codes.
393.9(a) — Inoperable required lamps has been cited 660,737 times in our database — more than four times the volume of 393.78 — and carries a 15.4% OOS rate. That is roughly 50 times higher than 393.78's 0.3% rate, meaning a lighting defect is far more likely to park your truck than a windshield defect.
396.3(a)(1) — Inspection, repair, and maintenance (general) presents the starkest contrast: 236,919 citations and a 45.3% OOS rate. Nearly half of all inspections that produce this code end with the vehicle out of service. A defective windshield is a problem; a truck that hasn't been properly maintained across multiple systems is a crisis in the eyes of an inspector.
393.47(e) — Slack adjuster defective sits closer to 393.78 in citation volume at 157,499 citations but carries a 0.0% OOS rate in that variant. The difference is that brake-related findings often fall under companion codes that do carry OOS weight. The lesson: 393.78 on its own is manageable, but it rarely shows up alone.
How to avoid it
Our co-occurrence data tells an important story: 393.78 almost never appears as a solo citation. In the last 90 days, it shared inspections with 393.9 (Inoperable Required Lamp) 3,550 times and with 396.17C (No proof of periodic inspection) 1,236 times. That pattern points to inspections where the overall vehicle condition is the problem, not just the glass. Address the windshield as part of a complete pre-trip, not as a standalone check.
Freightliner (FRHT) vehicles account for 25,936 all-time citations under this code — the most of any make in our database — followed by Kenworth (KW) at 16,961 and Peterbilt (PTRB) at 16,316. If you run one of these three makes, your pre-trip windshield check deserves extra attention.
Concrete pre-trip actions:
- Inspect the full windshield from outside the cab first. Walk to the front of the truck and look at the glass straight-on in daylight. Cracks and stress fractures are easier to spot from outside than from the driver's seat.
- Check the driver's direct sightline zone specifically. Inspectors focus on the area directly in front of the steering wheel. Any crack or chip in that band is a citation risk regardless of whether it feels minor from inside.
- Look for delamination and discoloration at the edges. Glass that is lifting from its seal or turning hazy at the perimeter can catch an inspector's eye during a walk-around.
- Document any pre-existing damage before a run. If a defect is present and repair isn't immediately possible, note it in writing, report it to your fleet manager, and get a work order open before departure.
- Pair this check with your lighting walk-around. Our data shows 393.9 (Inoperable Required Lamp) co-occurs with 393.78 in 3,550 inspections over the last 90 days. Confirm all required lamps are operational in the same circuit as your windshield check.
- Verify your periodic inspection documentation is current. With 396.17C appearing in 1,236 shared inspections, an inspector who writes 393.78 is very likely to also ask for your last inspection report. Have it accessible.