What is a “Truck Zone” in the United States?

I was recently on a trip, driving through Tennessee and came up on a bunch of semis going about 40mph down the interstate with their hazards on. There were one or two trucks that were still going regular speed, but most of them had slowed down. After about 1-2 miles I came to a sign that read End Truck Zone and the semis went back to regular speed. I never saw a sign saying where the truck zone begins.

I tried to look it up online, but there are no results on Google for "End Truck Zone" (with quotes), and most sites were just referencing the safe zone around a semi truck.

The closest thing I could find is in Australia. They have Truck Zone signs that say it’s legal for trucks to park on the side of the road in that area. That would make sense in this situation, since all the trucks were going slower, like there might be another truck on the side of the road, but I didn’t see any.

I also drove back the same way on the way home, and the experience was the same. Didn’t see a beginning sign, most trucks driving slowly with their hazards on, no trucks on the side of the road, and back to regular speed after the End Truck Zone sign.

So, what is the purpose of this zone?

Answer

I’ve found your END TRUCK ZONE signs.

This is about a 4.3 mile stretch of I-75 northbound, beginning 31 miles from downtown Knoxville, where trucks are restricted to the right lane. It begins at the end of the Exit 134 interchange, just before milepost 135, with signs reading TRACTOR TRAILER TRUCKS DO NOT PASS, and ends with the END TRUCK ZONE signs perhaps a quarter mile past milepost 139.

After reviewing this entire stretch of highway on Street View, I noticed that the 4% grade signs are on the opposite side of the highway.

The reason for this restriction, then, is that this stretch of road is a steeper uphill than it looks, and trucks would simply be unable to pass safely or without blocking traffic. This would also be why they were going slower than you expected. At the end of this zone it levels out, and trucks can get back up to speed.

From some truckers’ chatter I’ve read, I gather that there are several other spots along I-75 between here and the Kentucky state line where trucks slow down unexpectedly due to steeper than expected grades, though I didn’t go looking for all of them; I figure this example should be sufficient.

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