I have driven on the NJ Tpk many times and I noticed driving southbound, approaching exit 13A, between the sign that says Exit 13A - 1 mile and the exit, does not appear to be a mile long. The distance is off and looks like about 1/2 mile or so. I can tell this, because the distance between the 2 miles sign and the 1 mile sign looks like it is a mile long. There are other locations along the turnpike that have inaccurate distances. Exit 13, the next exit, has a very old sign on the cars only lane southbound, that reads: EXIT 13 [I-278 shield] Elizabeth - 2 miles .... then about 1/4 mile later, we see the more recent sign that reads EXIT 13 [278 shield] 1 mile, with 3 destinations (Elizabeth, Gothals Br, Verrazano Br). Another example is Exit 14-A-B-C.
Rather than speculating on what it "looks like," why not just take a look at your odometer or trip meter and use that to determine accuracy?
I was not the one driving. I meant I was a passenger. But I will take that suggestion, which is a fantastic one.
I do not think that mileage numbers on guide signs were meant to be accurate, but approximate. The one you should worry about is the "Trenton 30 Miles" sign at Exit 9 in the Truck Bus Lanes. It is not 30 miles to Trenton there anymore. The sign was erected before I-195 was built and you had to exit at Hightstown and use NJ 33. That is 30 miles, but via Exit 7A and I-295 is slightly longer than 30 miles even though it is the most direct and fast way now. No one at the NJ Turnpike Authority noticed that one yet!
I hope no one notices the old Trenton sign! It took me several trips just to photograph it. (I also hope no one notices the old one-way sign at Interchange [redacted]...)
As for your note, the NJ Turnpike Authority has had specific guidelines for years as to where signs can be located and what distances to show. These signs must be relics of before that policy was adopted and they just rounded to the nearest mile. They round to the nearest 1/4 mile now and will continue to do so.
For that matter, all those multiples-of-ten mileage signs ("Albany 120, Buffalo 400, Montreal 340" and the like, or whatever the relative intervals are) on the New York Thruway have always seemed a bit neat to me....
Some "excuses" if they ever wanted to go up against someone claiming to be hurt by wrong distance numbers.
This is meant to parody how silly life is nowadays to, like caution hot on coffee cups.
Exit mileage is only approximate, some settling in transit may have occured.
Caution distances between exits is closer than they appear.
Exit distances are guide signs only, it is up to the end user to know the distances.
Caution: Exit numbers have a 5% margin of error. NJ Turnpike is not liable for over or underage between exits.