US 75 Exit Numbers (Texas)

[The Ghostbuster]

Does anyone know why the US 75 freeway from Dallas north to Oklahoma was given sequential exit numbers? And does anyone know why only the portion of US 75 south, but not north of Interstate 635 later had their exits changed to mileage-based?

[NE2]

Because it bips.

[abqtraveler]

Does anyone know why the US 75 freeway from Dallas north to Oklahoma was given sequential exit numbers? And does anyone know why only the portion of US 75 south, but not north of Interstate 635 later had their exits changed to mileage-based?

Like many other states, Texas originally numbered its freeways sequentially, and then converted to distance-based exit numbering in the late 1970s.  At the time, TxDOT was only required to use mile-based exits on interstates, meaning non-interstate freeways remained unnumbered or retained whatever exit numbering scheme they already had in place.  With the completion of US-45 along the US-75 corridor between Dallas and Galveston, US-75 was decommissioned south of Dallas, and truncated to to its present terminus.  At the time of the exit number conversion in Texas, US-75 was the only non-interstate freeway with exit numbers in Texas, and since the conversion to mile-based numbers only applied to interstates, the sequential exit numbers on US-75 were left as-is.  More recently, the section of US-75 south of I-635 was reconstructed, resulting in the consolidation of several interchanges that were close together.  I don't know if the exit numbers were converted to mile-based numbering on this section, but they are significantly different than the numbers that existed prior to reconstruction.

[codyg1985]

The reconstructed portion of US 75 between I-45 and I-635 has exit numbers. Curiously, the exit numbers at the I=635 interchange jump from Exit 8 to Exit 20.

[The Ghostbuster]

I always found the exit numbers of this highway to be an oddity. The same sort of situation occurs on Interstate 95 in New York State. The highway starts out mileage-based, but then continues sequentially to the New York/Connecticut border. Of course, unlike Texas, New York has had sequential exit numbers from the get-go (excluding Interstate 99 and Interstate 781).

[Bobby5280]

They could get the exit numbers more consistent by extending I-45 North along US-75 into Oklahoma.

[Brian556]

Another weird thing is the mile markers with the word "mile" greened out; they even have them on the frontage roads

https://www.google.com/maps/@33.1026143,-96.6771582,3a,59.2y,341.43h,78.27t/data=!3m6!1e1!3m4!1ss1tXg2tI7qpv9EnAhRNUig!2e0!7i13312!8i6656

[abqtraveler]

I always found the exit numbers of this highway to be an oddity. The same sort of situation occurs on Interstate 95 in New York State. The highway starts out mileage-based, but then continues sequentially to the New York/Connecticut border. Of course, unlike Texas, New York has had sequential exit numbers from the get-go (excluding Interstate 99 and Interstate 781).

I don't know if the exit numbers are mile-based (post-consolidation) on US-75 south of I-635, but they definitely no longer match up with exit numbers north of that point.  Another point to consider is it would be interesting to see what mile-based exit numbers would really look like on US-75, since TxDOT uses a different method for numbering exits on non-interstates.  Instead of starting at the south or west end of the freeway, exit numbers on non-interstate freeways is based on the distance from a given reference point (either the northwestern-most corner of the Texas Panhandle, or the westernmost point in the state (where Texas, New Mexico and Mexico meet).  If the Texas Panhandle reference point was used, you'd see the lowest exit numbers at the Oklahoma border, with exit numbers increasing as you head south on US-75 (similar to the SH-130 toll road between Austin and Seguin).  Not sure what exit numbers would like if the westernmost point of Texas was used as the reference for exit numbering on US-75.

[MightyMG]

The mile markers on this stretch of 75 make no sense.  For one thing, they do not match the exit numbers.  But more puzzling is the fact that they are in the 230s in Plano, and decrease as they move northward.  So it wouldn't be a relic of pre-truncation US75.

I have been searching this forum in vain for the reason US75 mile markers are numbered this way.  Does anyone know?

[NE2]

That's standard Texas mile markers, measured (roughly) from the top of the Panhandle. I don't have a better description handy.

[Brian556]

It sounds like you guys are referring to reference markers, the tiny green markers that appear under reassurance signs
A while back, somebody provided a link to an online TxDOT document explaining these.

[J N Winkler]

It sounds like you guys are referring to reference markers, the tiny green markers that appear under reassurance signs

A while back, somebody provided a link to an online TxDOT document explaining these.

http://onlinemanuals.txdot.gov/txdotmanuals/trm/trm.pdf

The system works pretty much as Abqtraveler outlined above.  Milepointing starts with a pair of grid coordinates for a certain reference point along a non-Interstate route.  One coordinate is the distance in miles east from the extreme western point (the corner of Texas that pokes into New Mexico), and the other is the distance in miles south of the extreme northern point (the northern boundary of the Panhandle).  Mileage along the route is then surveyed from the reference point, and milepoints are derived by adding distance along the route to one of the coordinates.  If the route is mostly west to east, then the distance from the westernmost point is used, and if it is mostly north to south, then the distance from the northernmost point is used.

The little green signs always have three digits.  When read from top to bottom, each three-digit group is a whole-number mileage, zero-filled as appropriate.

AIUI, it is theoretically possible for a route to have multiple reference points and thus for there to be apparent gaps or overlaps in milepointing, though as far as I am aware, there are no cases where this has resulted in duplicate exit numbers.