Texas

[bwana39]

Video of the old SH-8 bridge over Lake Wright Patman being imploded.

https://www.kwtx.com/video/2025/03/06/txdot-demolishes-bridge-over-wright-patman-lake-state-highway-8-near-maud-texas/
https://www.youtube.com/watch?v=DlyVJJVAeM8

[ElishaGOtis]

There are currently no plans to expand the existing sections of SH 45. Hays County is starting the funding process for the southern link between FM 1626 and I-35 (the "SH 45 Gap") and a feasibility study is underway. Travis County opposes that construction however, and about a third of the route will be in Travis so I'm sure there will be lawsuits on the way (in fact I believe one was filed a few months ago over some dispute.)

TX-45 will never be a full loop around Austin. But, yeah, I think odds are very likely the Southern gap between FM-1626 and I-35 will be filled. There are few (if any) existing structures along the proposed path.

Once that gap is filled, I do believe it will put more pressure on extending the super highway NW to the FM-1826 intersection. There is plenty room between the existing frontage roads.

The US-290 freeway is planned to be extended about 11 miles from the Circle Drive Y to the East edge of Dripping Springs. Once that project is completed it will create more motivation to extend TX-45 about 3.5 miles NW to dovetail into US-290. There are long range freeway plan maps for the Austin metro that show TX-45 being extended to US-290. I'm sure there will be court battles. But they'll be like the ones fought over US-290 expansion in the Oak Hill area. Eventually people concede that something has to be done about the traffic. In the long run TX-45 could serve as part an East-West bypass for thru traffic to skirt Austin to the South. I do think the US-290 freeway will eventually be extended West to the US-281 corridor. Getting thru or around Dripping Springs won't be easy though.

Thought of this recently... Do y'all think any of these freeway extensions could have an 80-85mph design speed and speed limit? I'm curious as to whether or not any new roadways around that area could be built to a similar standard to the existing SH-45 high speed sections at 80mph...

[Bobby5280]

The TX-130 toll road is a unique case. The bypass goes through sparsely developed land on the East side of Austin. The terrain is more flat than the hilly areas West of I-35.

I wouldn't expect to see speed limits any faster than 70mph or 75mph on completed freeway sections of US-290 going out to Dripping Springs. If TX DOT builds a freeway around Dripping Springs to reach the US-281 corridor maybe that could get an 80mph limit (if the terrain is flat enough and sight lines are good enough).

The existing TX-45 toll road on Austin's South side has a 70mph speed limit. It's a skinny, minimalist design that's hardly any wider than some city streets. It has a shared use path next to it. Whatever gets built to fill the gap from its East end to I-35 may not be built much wider than that. Going West of the MoPac TX-45 had a wider foot print, thanks to the existing frontage roads. A future toll road West to US-290 would have a wider, more roomy ROW friendly to faster speed limits. But there is still a lot of hills and homes in that area. The location were TX-45 would dovetail into US-290 has a growing retail sector. I would expect slower speed limits there.

[sprjus4]

The TX-130 toll road is a unique case. The bypass goes through sparsely developed land on the East side of Austin. The terrain is more flat than the hilly areas West of I-35.

I wouldn't expect to see speed limits any faster than 70mph or 75mph on completed freeway sections of US-290 going out to Dripping Springs. If TX DOT builds a freeway around Dripping Springs to reach the US-281 corridor maybe that could get an 80mph limit (if the terrain is flat enough and sight lines are good enough).

The existing TX-45 toll road on Austin's South side has a 70mph speed limit. It's a skinny, minimalist design that's hardly any wider than some city streets. It has a shared use path next to it. Whatever gets built to fill the gap from its East end to I-35 may not be built much wider than that. Going West of the MoPac TX-45 had a wider foot print, thanks to the existing frontage roads. A future toll road West to US-290 would have a wider, more roomy ROW friendly to faster speed limits. But there is still a lot of hills and homes in that area. The location were TX-45 would dovetail into US-290 has a growing retail sector. I would expect slower speed limits there.

I honestly think we're not going to see any more 80 mph speed limits, unless there is a blanket increase statewide. Outside of the unique case of SH-130 / SH-45, and I-10 and I-20 in west Texas, Texas has not seemed interested in posting 80 mph speed limits anywhere else, even in areas that can easily handle them (I'm thinking of I-37, for example).

[Bobby5280]

Texas is an enormous state, but outside of segments of I-10 and I-20 the state doesn't have many other Interstate highways where an 80mph speed limit could be applied. I-35 is the only complete North-South I-corridor that goes across (and outside) the state. West of Fort Worth it's over 550 miles to the next North-South I-corridor in Las Cruces.

Perhaps portions of I-40 and I-27 in the Texas Panhandle could be given 80mph speed limits. They're mostly straight roads on mostly flat land. As far as I can tell they max out at 75mph currently. We have at least a couple turnpikes in Oklahoma which have segments signed with 80mph speed limits. These higher speed limits aren't just a Texas thing.

Maybe if I-27 is extended via the Ports to Plains Corridor effort it could carry 80mph speed limits on some of those new segments. If a lot more of I-69E, I-69C and I-69W are completed they could have 80mph speed limits. Those highways would pass through some very sparsely populated areas.

I don't know if I-37 would be a good enough candidate to have 80mph speed limits. It's an older highway. A bunch of its on/off ramp designs aren't so great for acceleration to or deceleration from 80mph speeds.

[sprjus4]

I don't know if I-37 would be a good enough candidate to have 80mph speed limits. It's an older highway. A bunch of its on/off ramp designs aren't so great for acceleration to or deceleration from 80mph speeds.

It's an older highway, but it's flat and wide open for virtually its entire length outside of San Antonio and Corpus Christi. Most traffic is comfortably moving 80+ mph.

I understand the ramp design concern, but if Texas is okay with a two lane road with at-grade intersections, turn offs, etc. being 75 mph, I can't see why a 5 mph bump on a limited access freeway with low volume ramps is the breaking point.

[ElishaGOtis]

I don't know if I-37 would be a good enough candidate to have 80mph speed limits. It's an older highway. A bunch of its on/off ramp designs aren't so great for acceleration to or deceleration from 80mph speeds.

It's an older highway, but it's flat and wide open for virtually its entire length outside of San Antonio and Corpus Christi. Most traffic is comfortably moving 80+ mph.

I probably will mention that Texas has the following speed limit caps:
- 85 if the design speed is 85 or higher
- 80 if the design speed is 80
- 80 on specified segments of I-10 and I-20 (regardless of design speed)
- 75 everywhere else (regardless of design speed)

Many freeways in TX that have a speed limit of 75mph only have a design speed of 70mph. Unlike other states, TX seems to be more focused on setting based on the 85th percentile rather than the design alone. They seem to emphasize this by frequently referring to the design speed as "inferred design speed."

I understand the ramp design concern, but if Texas is okay with a two lane road with at-grade intersections, turn offs, etc. being 75 mph, I can't see why a 5 mph bump on a limited access freeway with low volume ramps is the breaking point.

KE = 0.5mV^2 to be fairly honest...

[sprjus4]

I probably will mention that Texas has the following speed limit caps:
- 85 if the design speed is 85 or higher
- 80 if the design speed is 80
- 80 on specified segments of I-10 and I-20 (regardless of design speed)
- 75 everywhere else (regardless of design speed)

Correct, and only SH-130 and SH-45 have design speeds of 80 and 85 mph.

Those two roads and I-10 / I-20 are the only highways in Texas with a speed limit above 75 mph.

My point is, that should be amended to allow 80 mph not only on specified sections of I-10 / I-20, but also other rural interstate highways.

At least allow a study to be conducted to indicate if an increased speed limit would be safe, the same study that's done to determine 75 mph speed limits. I think it would find that a lot of rural interstate highways in Texas can safely handle the bump to 80 mph, including even I-30 in eastern Texas, I-40 across the Panhandle, I-27, and I-35 & I-37 south of San Antonio, etc.

I could even see 80 mph being safely implemented on the newly constructed 6 lane portions of I-10 between San Antonio and Houston, outside of urban areas. Especially as the rural portions continue to get widened further and further out. Similar to what Oklahoma did on I-44 west of Tulsa.

[Road Hog]

How much does governed truck traffic skew the 85th percentile though?

[ElishaGOtis]

I probably will mention that Texas has the following speed limit caps:
- 85 if the design speed is 85 or higher
- 80 if the design speed is 80
- 80 on specified segments of I-10 and I-20 (regardless of design speed)
- 75 everywhere else (regardless of design speed)

Correct, and only SH-130 and SH-45 have design speeds of 80 and 85 mph.

Those two roads and I-10 / I-20 are the only highways in Texas with a speed limit above 75 mph.

My point is, that should be amended to allow 80 mph not only on specified sections of I-10 / I-20, but also other rural interstate highways.

At least allow a study to be conducted to indicate if an increased speed limit would be safe, the same study that's done to determine 75 mph speed limits. I think it would find that a lot of rural interstate highways in Texas can safely handle the bump to 80 mph, including even I-30 in eastern Texas, I-40 across the Panhandle, I-27, and I-35 & I-37 south of San Antonio, etc.

I could even see 80 mph being safely implemented on the newly constructed 6 lane portions of I-10 between San Antonio and Houston, outside of urban areas. Especially as the rural portions continue to get widened further and further out. Similar to what Oklahoma did on I-44 west of Tulsa.

Can the design speed be re-calculated on an existing roadway based on existing conditions? FL does this sometimes, and ND conducted a study in this exact way to justify the speed limit increase from 75 to 80.