Your ultimate guide to the I-35 expansion through North Austin

A six-year effort to widen Interstate 35 through North Austin is already underway. Drivers are navigating shifting lanes and demolished bridges. New pathways are being plowed. Concrete is being poured.

But there’s still a long way to go.

So what is the Texas Department of Transportation (TxDOT) doing to the biggest road in Austin?

This is your ultimate guide to the I-35 Capital Express North expansion, one of three projects to enlarge the highway through Travis County. (We also have a guide to the far larger and more disruptive I-35 CapEx Central expansion. A guide to I-35 CapEx South is coming soon.)

I-35 CapEx North runs almost 11.5 miles from U.S. 290 East to SH 45 North near the border with Williamson County. Construction began in spring of 2023. TxDOT doesn’t expect the contractor to be done till early 2029.

That contractor is Pulice — whose trucks marked “PULICE” can almost look like law enforcement vehicles for a second. Pulice is based in Scottsdale, Arizona, but the company is actually owned by a gargantuan corporation called ACS. The Spanish firm was ranked the second-largest construction contractor in the world.

Pulice, at the direction of TxDOT, is adding one non-tolled “managed lane” in each direction. The managed lanes are also known as “high-occupancy vehicle” (HOV) lanes — reserved for vehicles with two or more people inside, along with first responders and public transit. The goal of HOV lanes is to keep traffic moving, but how vigorously the vehicle occupancy rule will be enforced remains an open question.

Other big pieces of the I-35 CapEx North project include:

• New bridges at Howard Lane, Braker Lane, Grand Avenue Parkway and Wells Branch. The bridges at St. Johns Avenue, U.S 183 and Parmer Lane will remain as is.
• A diverging diamond interchange (DDI) at Wells Branch Parkway. DDIs, which can be confusing at first, are a type of intersection where traffic is shifted to the left-hand side of the road to make turning left easier for cars. The bridge here will have an 8- to 10-foot-wide sidewalk down the middle of it between eastbound and westbound traffic.
• Intersection bypass lanes on the frontage roads at Howard Lane (northbound), Yager Lane/Tech Ridge Boulevard (northbound) and Rundberg Lane (both directions)
• New locations for some exit and entrance ramps
• Flyover ramps for CapMetro buses to exit the HOV lanes and drive directly to the Tech Ridge Park and Ride
• Sidewalks between 8 and 10 feet wide (also known as shared-use paths) along both sides of the highway
• Pedestrian crossings under the I-35 bridges over Walnut Creek and Little Walnut Creek (to be designed by TxDOT and constructed and maintained by the City of Austin)
• Five-foot-wide on-street bike lanes with a 2-foot buffer at the east-west crossings of Grand Avenue Parkway, Howard Lane, Braker Lane and Rundberg Lane
• Thirty-six boxes where bats can live under the I-35 bridge over Walnut Creek to replace some of the bat habitat lost by the demolition of the I-35 bridges over Howard Lane and Wells Branch Parkway
• Upgrades to drainage and other infrastructure that drivers don’t usually notice

We’ll take a deeper dive in the walkthrough below.

We’ve broken up the projects into intersections from north to south so you can jump ahead.

Navigate the guide

Who pays for the highway expansion?

The official budget for I-35 CapEx North is $606 million, paid for by the state and federal governments. Most of the federal money — drawn from the Highway Trust Fund — comes taxes on gas, diesel and other motor fuels. But the Highway Trust Fund hasn’t been breaking even for years. Since 2008, Congress has bailed out the fund with $275 billion, mostly with revenue from individual income taxes.

State highway dollars come from a variety of sources, including vehicle registration fees, excise taxes on Texas oil and gas production, and a portion of the state’s sales tax.

But highway expansions carry other costs, too.

Some of those include the forced relocation of five auto businesses after TxDOT expropriated 17 acres of land to grow the highway’s footprint. The state provides property owners financial compensation through the eminent domain process, but many costs — including the stress of having to move — often go uncompensated.

Adding 23 miles of lanes to I-35 in North Austin will draw more cars and trucks to the highway. TxDOT predicts I-35 vehicle volumes from Rundberg Lane to Howard Lane will increase by more than 30% by 2045. “Vehicle miles traveled,” another metric that adds up the total distance traveled by all cars and trucks, is expected to rise by 54% by 2045.

TxDOT’s environmental analysis claims toxic air pollutants like benzene, formaldehyde and tiny particles that invade the lungs will actually decrease as more cars flood the interstate. Same for greenhouse gas emissions. The eyebrow-raising claim is based on a federal government simulator assuming vehicles will become so fuel efficient that air quality will improve even as traffic volumes increase.

An online calculator by RMI — a Colorado think tank focused on sustainability, previously known as the Rocky Mountain Institute — says adding 23 lane miles to I-35 in Austin would add between 700,000 and 2.2 million metric tons of carbon dioxide cumulatively through 2050.

For context, 1 million metric tons of carbon dioxide is equivalent to the CO2 emissions generated by burning more than half-a-million tons of coal, according to the U.S. Environmental Protection Agency.

In its environmental assessment of greenhouse gases, the state says: “Such changes cannot be accurately predicted due to the inherent uncertainty in future projections related to demographics, social change, technology, and inability to accurately forecast where people work and live.”

Traffic noise will get louder. Of 91 locations TxDOT tested — including schools, day cares, places of worship, medical centers, funeral homes and cemeteries — 52 sites would have noise levels increase close to or beyond federal standards.

The state is installing eight noise barriers to block some of the traffic sound. But they’ll only be placed in front of 11 of the 52 locations. For the rest, a noise barrier was found to be either too expensive — based on a federal cost limit of $25,000 per benefited location — or not effective enough.

Construction will at least temporarily disrupt vegetation and wildlife habitat, including the removal of certain trees and ground cover that provide erosion control and habitat for migratory animals. TxDOT says those areas will be reseeded and restored and the disruption will be “largely temporary.”

Legend

Let’s take a closer look at what is actually happening to I-35 between U.S. 290 East and SH 45 North.

Don’t be intimated by these schematics. You don’t need to be a highway engineer to understand them. You just need to know a few things first. The maps are oriented sideways so left is north.

Now take a look at this legend. Yes, it’s a lot. Some colors in the map don’t even appear in the legend. Don’t worry about everything. Here are just a few things to keep in mind.

Yellow shows the general purpose lanes that will be widened or reconstructed. The teal or light-blue streak represents the new managed lanes. Dark gray shows previous projects that were completed before the I-35 CapEx North project, for example, the reconstruction of the St. Johns Avenue bridge that finished in 2020.

Sometimes the colors don’t correspond to the legend at all.

To demystify some important jargon: ROW stands for “right-of-way,” which is basically the highway land TxDOT controls.

Highway layout

Here’s a very basic before and after cross-section of I-35 CapEx North. This will vary throughout the project’s length, but the illustration offers a general idea of what’s changing. We’ll have more specific cross-sections below.

Unlike the I-35 CapEx Central project, where virtually all lanes will be narrowed to 11 feet, I-35 CapEx North will retain many 12-foot-wide lanes. The managed lanes will be 12 feet wide. During construction, however, many temporary lanes will be slimmed to 11 feet.

Let’s start our tour on the northern edge of this highway expansion.

SH 45 North

I-35 CapEx North technically begins slightly inside the Williamson County line; the boundary between the two counties is a bit south of SH 45 North, but there aren’t any big changes planned in this area.

The project doesn’t include any more flyover ramps providing direct connections between SH 45 North and I-35. Those are planned as part of TxDOT’s expansion of I-35 from Round Rock to Georgetown, which is still being studied. Detailed schematics might not be available till 2025.

On this section of map, the thick light-green line shows “shared-use paths,” which are essentially sidewalks between 8 and 10 feet wide that both pedestrians and cyclists can use. These shared-use paths will run on both sides of the highway along the entire length of I-35 through Travis County.

One other feature of the I-35 expansion featured here that you’ll find throughout: so-called “slip lanes,” those right-turn lanes where drivers can quickly bypass the normal intersection to turn right. They’re convenient for drivers, but can be dangerous for pedestrians to cross without any stop sign or traffic signal.

Perhaps the biggest change in the above section: a new southbound exit ramp is planned just north of Parker Road.

Moving farther south, you get a better picture of what’s going on with the southbound ramps.

TxDOT is doing what it calls a “ramp reversal” in this area, opening a new exit ramp and closing a southbound entrance ramp. It’s something TxDOT engineers say reflects updated highway design standards.

When I-35 was built decades ago, engineers thought it would make sense to have ramps exit just before the intersection you’re trying to access. But when traffic gets busy during rush hour, a line of vehicles can back up into the main lanes.

In this case, the ramp reversal comes south of SH 45 North, which could get direct connector ramps to I-35 with that upcoming expansion in Williamson County. TxDOT believes this could also increase access to businesses along the frontage road.

In the above section near Gilleland Creek, TxDOT plans to close the northbound exit ramp. It’s being shifted south, as you’ll see in the coming schematics.

Let’s take a closer look at Gilleland Creek. This is one of nine creeks I-35 CapEx North project crosses. The others are Walnut Creek, Little Walnut Creek and a bunch of unnamed tributaries. Some of the creeks carry water only at certain times of year.

The purple-shaded area represents the 100-year floodplain, which is land that has a 1% chance of flooding in any given year. TxDOT says the highway is being constructed to allow for the inundation of the roadway during a 100-year flood without causing damage to the road or nearby property.

Gilleland Creek, which flows 32 miles into the Colorado River, naturally starts from Ward Spring outside Pflugerville. But runoff from I-35 and SH 45 North have caused the creek to start farther north.

TxDOT claims highway construction and usage will have relatively minor permanent impacts on the creek.

As we move farther south toward the intersection of I-35 and Grand Avenue Parkway, you can see where the northbound managed lane exits. The shaded yellow shows more frontage road lanes.

The southbound exit ramp to Grand Avenue Parkway will be closed, and a new entrance ramp will open – part of the ramp reversal mentioned above.

Grand Avenue Parkway

Grand Avenue Parkway runs beneath I-35. The highway bridge over this local cross-street will be widened to accommodate five lanes in each direction.

When complete, I-35 over Grand Avenue Parkway will have 12-foot-wide lanes and 10-foot-wide outside shoulders. The inside shoulders will vary between 4 and 10 feet wide.

TxDOT reconstructs bridges in phases. One side comes down. Traffic is shifted over. When the new bridge is done, the other side is demolished and rebuilt.

Contractors are required to keep at least three main lanes open in each direction with an exception for occasional closures during off-hours like evenings and weekends.

As you can see from the yellow shading in the schematic below, TxDOT will widen the turnaround lanes at Grand Avenue Parkway and add a dedicated right-turn lane to the I-35 southbound frontage road.

You can’t tell in the above schematic, but this more detailed layout shows a traffic island, too. The slip lane, like many along the project, won’t have a traffic signal. So pedestrians may have to wait for their chance to cross and then make a break for it.

On the northbound side, the frontage road will have double right-turn-only lanes at Grand Avenue Parkway. Right now, there’s only one right-turn-only lane heading north. The new double right-turn lane will have a traffic signal with a pedestrian push button.

East of I-35, Grand Avenue Parkway is a divided road with center medians. Those medians will be narrowed and Grand Avenue widened to three lanes in each direction from Vision Drive to Central Commerce Drive.

Here’s a section of that stretch of Grand Avenue. The shaded yellow shows the new pavement.

South of Grand Avenue Parkway, TxDOT is planning again to shift entrance and exit ramps. The schematic says “EXIT RAMP TO BE CLOSED,” but that should read “ENTRANCE RAMP TO BE CLOSED.” The ramp is being moved farther north.

The existing entrance ramp looks like this.

As you can see in the schematic, the northbound entrance ramp will connect with that long merge lane, allowing drivers on the northbound frontage road to bypass the traffic signals at Grand Avenue Parkway.

Farther south, just past Pamela Street, is a second opportunity for drivers to enter the southbound managed lanes.

An entrance to the northbound HOV lane is just north of Wells Branch Parkway. But you’d have to enter I-35 about a mile before Wells Branch to get there.

The existing northbound exit ramp just north of Wells Branch Parkway will be closed. A new northbound exit ramp will open about a quarter mile up the road, as shown in the earlier schematic.

The “PROPOSED NEW ENTRANCE RAMP” heading southbound in this section already exists. But TxDOT plans to change the geometry slightly to make the ramp a little bit straighter.

A bit south of that southbound entrance ramp, the southbound frontage road will grow from two lanes to three.

Wells Branch Parkway

Wells Branch Parkway will undergo the biggest change of all the intersections along the I-35 CapEx North project. TxDOT is planning to install something called a “diverging diamond interchange” (DDI) here.

DDIs can be confusing. When you’re crossing the bridge, car lanes shift from the right to the left side of the road. This allows drivers to turn left on to the frontage road without crossing against oncoming traffic.

Take a closer look at the schematic to understand how the DDI lanes at Wells Branch will be configured. A shared-use path that will be 8 to 10 feet wide — shown on the schematic in purple for some reason instead of green — will cut in the middle of the interchange with three lanes of traffic on either side.

This 10-year-old TxDOT video explains how to drive the first DDI that opened in the Austin-area: at I-35 and University Boulevard in Round Rock, near the IKEA.

Highway engineers say DDIs improve the flow of cars and trucks by simplifying left-hand turns. Having fewer conflict points reduces the risk of a T-bone crash. But DDIs have drawbacks, too.

Pedestrians will have to cross the road up to four times to get to the other side of the interstate. At least two of those pedestrian crossings — again the single right-turn-only “slip lanes” — won’t have any traffic signals, according to TxDOT’s more detailed technical documents.

For drivers on the frontage road, continuing northbound or southbound won’t be possible at Wells Branch Parkway. You’d have to get on a bypass lane that skips the intersection. If you miss the bypass lane, you’d need to turn right down Wells Branch, do a U-turn at the next intersection and backtrack to the highway.

The first DDIs within Austin opened in 2020: at MoPac and Slaughter Lane and about 1 mile south at MoPac and La Cross Avenue. The most recent DDI to open was at I-35 and Parmer Lane, which will remain unchanged as part of the I-35 CapEx North project.

The DDI at Wells Branch Parkway will be the fifth in the Austin area and the first at ground level. The others have been on bridges. A sixth DDI planned at Loop 360 and Courtyard Drive/2222 will also be at ground level.

Other changes in this area of I-35 include rerouting the northbound frontage road approaching Wells Branch to allow for a wider angle of approach to the DDI.

You’ll still be able to do a U-turn at Wells Branch to switch directions northbound or southbound. But the turnaround lanes will have traffic signals, because they’ll be part of the bigger interchange.

The I-35 bridge over Wells Branch Parkway has been home to thousands of bats. Same for the highway crossing over Howard Lane. TxDOT hired a company to try to get the bats out from under the northbound bridge before it was torn down. Both bridges will be reconstructed so bats can live there again.

The new Wells Branch bridge will be bigger. The span will have four 12-foot-wide general-purpose lanes going northbound. But the southbound lanes will mostly be 11 feet wide, much like the narrowed lanes coming to I-35 through Central Austin.

South of Wells Branch Parkway, both frontage roads will widen by one lane. Drivers will be able to exit the southbound managed lane here, but not soon enough to get off at Howard Lane, the next major intersection. The next southbound exit from the main lanes isn’t until after Howard.

The existing southbound exit ramp in this area will be closed and shifted a bit farther south. The northbound entrance ramp will also be shut and moved south.

This is also where we start to see the first of eight noise barriers installed along the widened highway.

More cars mean more noise, and federal regulations require TxDOT to turn down the volume if it gets too loud.

But there’s a catch.

TxDOT has to install noise barriers only if they don’t exceed a federal cost limit. The threshold is $25,000 per “receiver,” which is a sound sensor placed at homes or businesses with a line-of-sight to the highway.

If a noise wall costs more than $25,000 to build per benefited receiver, the barrier is not considered “reasonable” and isn’t required under federal law.

Same deal if the barrier fails to reduce noise levels by at least 5 decibels for at least half of the households closest to the highway. Such noise abatement isn’t considered acoustically “feasible” and is not required.

Dozens of locations along the I-35 CapEx North project — including homes, schools, playgrounds, churches and medical facilities — will hear louder traffic noise because of the highway’s increased capacity.

But because 20-foot-tall noise barriers would not achieve a big enough reduction in volume at a low enough price, only 11 of 52 locations expected to have traffic noise approaching or exceeding federal standards will get a noise wall.

Lantower Ambrosio Apartments on the east side of I-35 south of Wells Branch will get a 510-foot-long noise wall that’s 16 feet high. The estimated cost of the noise wall is $146,880 — about $8,160 per affected household.

The other noise barrier in this section will be at the Vineyard, an apartment complex also east of I-35 but south of Lantower Ambrosio. The sound wall will be 478 feet long and 16 feet tall, shielding 21 homes from traffic noise at a cost of $137,664.

Cook-Walden/Capital Parks Funeral Home and Cemetery, southeast of the I-35 intersection with Wells Branch Parkway, is one of two cemeteries right next to the highway expansion project. The other is Cook-Walden Memorial Hill Cemetery.

A general manager with Cook-Walden confirmed to TxDOT by e-mail that no graves exist outside the fenced-in boundaries of either cemetery. All construction work in that area is supposed to happen within the footprint of I-35, so TxDOT concluded it should not be concerned about affecting any unmarked graves.

Both cemeteries will get louder because of the increased traffic on I-35. Cook-Walden Capital Parks Cemetery will have a 5-decibel increase, according to a TxDOT’s technical report on noise. For reference, a 10-decibel increase sounds like something is twice as loud, so a 5-decibel increase would still be noticeable.

But because the Capital Parks Cemetery is already relatively quiet, the 5-decibel increase wouldn’t increase noise to a level where the FHWA would require TxDOT to do something about it, like install a noise barrier.

Traffic noise at Memorial Hill Cemetery would increase by 2 decibels, by TxDOT’s estimate. Sound levels at that cemetery already exceed federal standards. But TxDOT says a 20-foot-tall noise barrier wouldn’t reduce the noise by the federal minimum of 5 decibels, so the state is not required to build one.

Howard Lane

As we continue south on our tour of the I-35 CapEx North project, we approach Howard Lane.

The schematic says an entrance ramp on the northbound frontage road immediately north of Howard Lane will be closed. No such entrance ramp exists, so it can’t be closed.

But there is an exit ramp there. This will be shifted slightly north, as indicated by the “PROPOSED NEW EXIT RAMP” text.

A bigger change in this section will be the addition of a new northbound bypass lane, allowing drivers on the frontage road to avoid the intersection at Howard. The bypass lane will — as indicated in orange, which means “bridge” — rise up over Howard Lane.

Drivers on the northbound bypass lane over Howard will have the option of merging onto I-35 before Wells Branch.

But drivers accessing northbound I-35 from Howard will no longer be able to merge on the main lanes before Wells Branch. Only drivers on the bypass lane will have access to that northbound I-35 on-ramp.

So if you regularly drive from Howard to I-35 northbound, you’ll need to get on the next bypass lane to skip the Wells Branch intersection, then merge onto the main lanes a bit before Grand Avenue Parkway.

On the southbound frontage road, the “PROPOSED NEW ENTRANCE RAMP” approaching Howard Lane is really just a slight southward shift of the existing entrance ramp.

After Howard, northbound frontage road drivers pass by the second burial ground adjacent to the I-35 project: Memorial Hill Cemetery. As mentioned in the Wells Branch section, traffic noise would get louder at this graveyard.

A sound barrier is not required at Memorial Hill Cemetery under the FHWA’s calculation, because a 20-foot-tall noise wall wouldn’t drop traffic volumes by at least 5 decibels, according to TxDOT, so one will not be constructed.

The southbound frontage road approaching Howard Lane will be widened to three lanes from two.

Now let’s zoom in to the intersection of Howard Lane and I-35.

The bridge has been habitat for thousands of bats. TxDOT tried to evict all the bats on the northbound side before tearing down the bridge in October. The new, larger bridges will be constructed in such a way that bats could roost there again.

After the new bridges are rebuilt and the highway is completed, I-35 at Howard Lane will have in each direction: three main lanes, one long merge lane and one managed lane.

You can see in the cross-section the elevated northbound “CD LANE” (collector-distributor lane) that will allow people to bypass the intersection at Howard.

The configuration of Howard Lane underneath I-35 will change, too.

After the highway project is complete, Howard will gain a center median. Twelve-foot-wide shared-use paths will run along both the eastbound and westbound lanes. The width of the turnaround lanes will grow 40% from 17 feet to 24 feet.

Both northbound and southbound I-35 frontage roads at I-35 will have a dedicated right-turn lane. The slip lanes will have no traffic signal to stop cars for pedestrians trying to reach the traffic island.

The southbound frontage road south of Howard will briefly grow to three lanes, so northbound drivers switching directions via the U-turn lane will have more time to merge.

Farther south, the southbound exit ramp and northbound entrance ramps will shift a little, but basically stay in the same locations. The southbound exit ramp will widen to two lanes.

Not shown in these schematics is a plan to build flyover ramps exclusively for CapMetro buses to exit the managed lanes for the Tech Ridge Park and Ride. The bus stop at 900 Center Ridge Drive lets people leave their cars and take the following routes:

TxDOT says it doesn’t yet have a detailed schematic for the so-called T-ramp for CapMetro buses. But this map gives an idea of how the lanes would work. Buses could enter and exit the bridge to go north or south.

This cross-section of the T-ramp shows how the CapMetro lanes would gain elevation before buses could turn onto the bridge.

CapMetro has been working closely with TxDOT on the T-ramp design and other aspects of the I-35 project. The transit agency says it will take advantage of the HOV lanes.

“We also anticipate having the quality level of experience that we have seen with our Express network on MoPac with similarly managed lanes in place — to where we have previously seen record level ridership for bus service in/out of Downtown/UT with improvements in travel time and directness,” CapMetro spokesperson Jorge Ortega told KUT in a statement.

As we approach Parmer Lane, you can see how the existing northbound bypass lane was closed a few years ago, even though the schematic says “TO BE CLOSED.” These preliminary schematics are a few years old.

The northbound lanes north of Parmer will gain a long merge lane, also known as an auxiliary lane.

Parmer Lane

TxDOT doesn’t have a ton of work planned around Parmer Lane at I-35, because the bridge was already rebuilt and converted to a diverging diamond interchange in 2022.

The schematic does show the southbound bypass lane under Parmer growing from one lane to two. The shaded yellow areas, including underneath the Parmer Lane bridge, indicate pavement widening or reconstruction.

A long merge lane — also known as an auxiliary lane — runs alongside the northbound main lanes, traveling from south of Parmer all the way to the next exit north of Howard Lane.

South of Parmer, a new northbound entrance ramp is coming. A little farther south of that, a northbound bypass lane planned to cross over Tech Ridge Boulevard will split to the entrance ramp and the frontage road.

The southbound frontage road north of Yager Lane/Tech Ridge widens to four lanes until the southbound entrance ramp.

Yager Lane/Tech Ridge Boulevard

The bridge over I-35 at Yager Lane/Tech Ridge won’t be rebuilt for the I-35 CapEx North project, but a new two-lane bridge on the northbound frontage road will let people bypass the intersection.

If you can tolerate looking at this busy technical illustration, you’ll get a better visualization of how the northbound bridge will pass over Tech Ridge Boulevard. Imagine standing on the east side of I-35 looking west. The 918-foot bypass bridge will be at least 17 feet above Tech Ridge.

One of the eight planned noise barriers will be constructed at an apartment complex called the Upland North ATX east of I-35 and south of Tech Ridge. The $434,160 barrier will be 1,206 feet long and 20 feet high.

A TxDOT noise test simulating what the expanded highway would sound like from the first-, second-, third- and fourth-story balconies found the noise barrier would reduce traffic sound by at least 5 decibels at about half the homes. For reference, a 10-decibel reduction would sound half as loud.

The shaded pink area in the bottom right of the schematic map above is supposed to indicate a “construction easement,” which is basically private property that’s expropriated so TxDOT can position equipement or materials. This is also where a shared-use path is now and will remain after the project is done.

The next section of schematic we’ll look at is immediately south of Yager Lane/Tech Ridge Boulevard. The northbound frontage road will be resurfaced. Most of the southbound frontage road in this area will grow by one lane.

Next to the yellow northbound frontage road are the yellow northbound bypass lanes that lead into the bridge passing over Tech Ridge.

Drivers will get on that northbound bypass lane over Tech Ridge farther south at the area labeled “PROPOSED NEW RAMP,” accessible from the frontage road. Drivers on the main lanes will have a chance to merge on the Tech Ridge bypass lane a bit farther south.

Say goodbye to the northbound entrance ramp just south of Yager/Tech Ridge.

On the southbound side of the highway, an exit ramp is closed and a new entrance ramp is opened just south of Park 35 Circle. Some people expressed concern to TxDOT about the location of that onramp during public feedback for the project.

Residents said people leaving Park 35 Circle — a street that connects to the Central Texas Girl Scouts headquarters, the Texas Commission on Environmental Quality campus and other homes and businesses — wouldn’t have enough distance to cross three frontage road lanes and accelerate onto the I-35 entrance ramp.

TxDOT said the on-ramp is 300 feet south of the intersection at Park 35 Circle, meeting “the minimum design criteria standards.” Moving the on-ramp farther south would have forced out more businesses, the agency said.

People trying to get on I-35 southbound from Park 35 Circle can either make a right turn on the frontage road and wait for a moment to accelerate into the entrance ramp or they could backtrack, taking Walnut Park Crossing to Lamar Boulevard to Yager Lane to I-35.

Continuing along our tour, we arrive at Walnut Creek where the I-35 bridges are being reconstructed.

Walnut Creek is one of the nine creeks and streams the highway passes over in the I-35 CapEx North project. The others are Little Walnut Creek, Gilleland Creek and some unnamed tributaries.

The creek could provide good habitat for the Texas fatmucket and Texas fawnsfoot, freshwater mussels declared endangered by the U.S. Fish and Wildlife Service. TxDOT said in its environmental assessment that a 2015 survey of the area didn’t find any of those mussels.

The main lane bridge over Walnut Creek will grow significantly, expanding from six lanes to 12.

On the frontage road bridges over Walnut Creek, the existing sidewalks are just 4 1/2 feet wide. Pedestrians must walk next to cars going by at 60 mph on one side and a railing with a long drop to the creek below on the other side. It’s about as nerve-racking as any sidewalk along I-35.

The new sidewalk over Walnut Creek will be 14 feet wide with a steel railing between pedestrians and traffic. On the other side of the railing will be a 6 1/2-foot shoulder, putting even more space between cars and people.

Beneath the I-35 bridge over Walnut Creek, crews have already installed 36 bat boxes intended to replace bat habitat lost by the destruction of the Howard Lane and Wells Branch bridges. The boxes cost up to $4,000 each and were designed with help from Bat Conservation International.

One bat expert says the boxes won’t provide enough habitat to replace the lost roosts.

“It doesn’t seem like the most ideal habitat. It’s down below the level of the surrounding landscape. But it’s a nice gesture,” Lee Mackenzie with Austin Bat Refuge, one of several bat organizations TxDOT consults, told KUT News. “They can’t build enough for the number of bats in … both bridges.”

In a yet-to-be-publicized pedestrian improvement, TxDOT and the City of Austin are working to build trail crossings under I-35 at Walnut Creek and Little Walnut Creek.

“TxDOT is designing and constructing openings under I-35 to accommodate trails that will be constructed by the City,” said Jack Flagler with the City of Austin’s Transportation and Public Works Department.

For the Walnut Creek connection, the city is in the early engineering stages. For the Little Walnut Creek connection, which we’ll look at below, construction funding was recently secured through a federal Safe Streets and Roads for All grant, Flagler said. Design work will start soon.

As you can see in the schematic, the southbound frontage road would remain two lanes wide while the northbound frontage road would grow from two lanes to three at Walnut Creek.

A new northbound exit ramp would be installed a little bit past the bridge.

In both directions, drivers would be able to enter the managed lanes a few hundred yards south of Walnut Creek.

The longest noise barrier along the I-35 CapEx North project will be installed on the east side of the highway between Walnut Creek and Braker Lane. The half-mile-long noise wall should turn down the traffic volume by at least 5 decibels in the North Oaks neighborhood.

The $1 million barrier will be 20 feet tall and broken into segments so as not to block streets leading to I-35.

North of Braker Lane, what is now a southbound entrance ramp will be converted to a southbound exit ramp.

The northbound exit ramp north of Braker Lane gets shifted slightly south. The northbound frontage road grows wider.

The main lanes are still wider here with four lanes instead of three.

Braker Lane

The Braker Lane bridge over I-35 will be rebuilt. The biggest change will be the addition of U-turn lanes in both directions. They’ll be constructed as separate bridges over the highway. The northbound turnaround will be installed before the Braker Lane bridge is reconstructed, planning documents say.

Both frontage roads will get extra turn lanes for the turnaround. Apart from those, frontage roads will remain three lanes in each direction at Braker.

Beneath the bridge, I-35 will have four northbound lanes and five southbound lanes. The southbound side includes a long merge lane for drivers on the frontage road to bypass the Braker Lane traffic signal.

Right now, the Braker Lane bridge over I-35 has a standard sidewalk and an unprotected bike lane running on each side.

After the new bridge is built, 12-foot-wide shared-use paths will run on both sides of the crossing. The lane configuration for vehicles on the bridge will remain basically the same.

A live oak tree believed to be 700 years old is northeast of this intersection. The tree would have started growing around the time the Ottoman Empire was established and the Black Plague began sweeping across Europe.

Now, it’s in the parking lot of a Northern Tool + Equipment.

TxDOT has vowed to protect the 5-foot-thick tree on the northbound I-35 frontage road. A certified arborist is supposed to be on site whenever construction work happens near the oak.

Farther south of Braker, the northbound entrance lane will shift slightly north. The southbound exit lane moves farther south. The main lanes grow from three to four.

In this next section — I-35 around Diamondback Trail and Applegate Drive — drivers on the northbound managed lanes will be able to exit as they approach Braker Lane.

On the far bottom right of the image, you can see where drivers could enter the southbound managed lane north of Rundberg, the next intersection.

The southbound exit lane just south of Braker will be closed. Drivers who want to exit I-35 for Rundberg Lane will have to use the new southbound exit lane north of Braker and wait at the Braker Lane stop lights.

The main lanes grow from three to four between Braker and Rundberg Lane. The frontage roads each gain a lane, as indicated by the yellow shading.

We have arrived just north of Rundberg Lane. A lot more is going on here.

Two bypass lanes in each direction will let drivers on the frontage roads take a bridge right over the Rundberg Lane intersection.

The southbound managed lane will have an exit just north of Rundberg as indicated by the green arrow. The exit will give drivers on the managed lane enough time to get on the U.S. 183 exit.

Rundberg Lane

Demolition has already begun on the I-35 bridge over Rundberg Lane. The crossing will be rebuilt larger one side at a time.

Once complete, I-35 at Rundberg will have the HOV lanes, three northbound lanes and three southbound lanes and a long merge lane. Two bypass lanes in each direction will let drivers on the frontage roads avoid the intersection without merging onto the main lanes.

The U-turn lanes under I-35 will be shifted outward — as indicated by the new yellow-shaded lanes replacing the red thatched area, which represents existing turnaround lanes.

Moving the U-turn lanes will create space for 12-foot-wide sidewalks on both sides of Rundberg Lane under I-35, as you can hopefully make out in this technical illustration.

You can’t tell in that illustration, but three existing slip lanes will be kept in the northwest, southwest and southeast corners of the intersection. Here’s a diagram showing the planned pavement makings on the east side of the highway at Rundberg.

One of the eight noise barriers being installed as part of I-35 CapEx North will be inserted on the west side of the highway south of Rundberg Lane. The walls are intended to block additional traffic noise for people living at the Starburst and Orbit apartment complexes.

The 912-foot-long wall will be 20 feet tall and broken into five segments so it doesn’t block driveways. Most, but not all apartments, would have a sound reduction of at least 5 decibels, TxDOT says. The estimated cost of the barrier is $328,320.

On the northbound side of the highway, an entrance ramp at Henna Chevrolet will be closed. Instead, drivers on the northbound frontage lane could get on the bypass lanes a bit farther south and merge into the main lanes after Rundberg.

Approaching Little Walnut Creek, southbound I-35 narrows from four main lanes to three.

To build the southbound bypass lanes at Rundberg Lane, TxDOT expropriated almost 0.7 acres of land from the Upper Little Walnut Creek Greenbelt.

Most of the land was taken from existing City of Austin parkland on the west side of I-35. But some proposed parkland was taken on the east side, too.

As a way to “mitigate” the seizure of parkland, TxDOT is designing a bicycle and pedestrian crossing under I-35 at Little Walnut Creek. It should be ADA accessible and have lighting. The 10-foot-wide bridge will be built and maintained by the city.

A design of the actual bridge isn’t ready yet, but this cross-section shows the pedestrian path would travel under the I-35 bridge over Walnut Creek. The main lane bridge over Little Walnut Creek will be higher than the frontage road bridges.

As far as the ramp changes are concerned, southbound drivers who want to get on U.S. 183 would merge from the main lanes or the frontage road to a two-lane ramp.

Northbound drivers on the frontage road could get on a bypass lane to skip the Rundberg intersection and merge on the main lanes farther north.

On the west side of I-35 north of U.S. 183, another noise barrier is planned, as indicated by the narrow blue lines. These are to block sound for the people living at Towne Oaks 1 Apartment complex. The $46,260 barrier will be 257 feet long and 10 feet wide.

This section shows the southbound exit ramp continuing to the flyover connecting to U.S. 183. Frontage roads on both sides remain three lanes wide.

Again, you can tell how many lanes there are by counting them or by looking at the little numbers in white circles.

U.S. 183

In 2022, TxDOT cut the ribbon on three new flyovers at U.S. 183 and I-35. Those are indicated in the schematic in dark gray.

As the southbound main lanes pass under U.S. 183, the entrance ramp joins and expands the main lanes from three to four.

The managed lanes continue beneath the interchange without entrances or exits.

Otherwise, there aren’t a lot of changes planned around U.S. 183 because of all the work already done over the last few years.

St. Johns Avenue

The last bridge on our tour is at St. Johns Avenue. This crossing over the highway was reconstructed with new U-turn lanes in 2020, part of the same $124 million project that added three flyovers at U.S. 183.

The project included bypass lanes allowing drivers on the frontage roads to avoid the intersection. As part of I-35 CapEx North, more bypass lanes are coming to Howard Lane (northbound), Yager Lane/Tech Ridge Boulevard (northbound) and Rundberg Lane (both directions).

I-35 southbound grows to five lanes at this point including the long merge lane.

And that takes us to the last stop on our tour.

I-35 CapEx North project spans almost to U.S. 290. That’s where the I-35 CapEx Central project picks up and runs 8 miles south to Ben White Boulevard.

The entrance and exit ramps for the managed lanes in North Austin will be situated just north of the U.S. 290 interchange.

Learn more

Construction of the I-35 CapEx North project is supposed to wrap up in early 2029. Until then, expect lane and bridge closures, construction noise and dust. TxDOT says the contractor, Pulice Construction, must keep at least three lanes open in both directions except for occasional closures that may happen during evenings or weekends.

If you would like to brave diving into the technical documents to learn more detail about particular areas or future traffic-control plans during construction, we’ve made all 4,000+ pages of the 100% plans available for download. The 1.85 GB zipped file includes six PDFs.

You can also download the TxDOT schematic, which is a less detailed PDF, but easier to read if you can zoom in and out.