The route begins in a downtown. I-35’s southern end is not a junction with another Interstate or a ring road around a port city but a bridge over the Rio Grande in central Laredo, and the Texas Department of Transportation’s 2018 profile of its Laredo district describes what sits there: the Laredo World Trade Bridge, at the southern terminus of I-35, which that document calls the largest land port of entry in Texas and on the southern U.S. border, and the second largest commercial land port of entry in the country after Detroit.
Land ports are ranked by what crosses them, and the crossing at Laredo is overwhelmingly rubber-tyred. The district has eight vehicular international crossings and one rail crossing, and four of the eight take commercial traffic. Everything that clears those four gates and is bound for anywhere north of Webb County joins the same road.
The border numbers, with their years attached
TxDOT’s corridor plan for the route, published in October 2016, reports that more truck traffic passed through the Port of Laredo in 2015 than through any other border crossing in the United States, with over 2 million trucks entering the country there that year, more than three times the number entering at any other Texas port. Citing federal transportation statistics, the same plan puts Laredo’s share at approximately 53 percent of the daily truck volume between Texas and Mexico in 2015.
Those are 2015 figures published in 2016 and they should be read as such. What the plan offers about the trend is a rate rather than a level: the number of trucks crossing the international border into Laredo via I-35 rose 170 percent over the twenty years preceding the plan.
The number of trucks crossing the international border into Laredo via I-35 has increased 170 percent in the last 20 years.
The trade agreement usually credited with that growth is in the plan too, with a figure and a source attached. The North American Free Trade Agreement was signed in 1993, and citing the International Trade Commission’s tariff and trade data, the plan states that U.S. goods and services trade through NAFTA totalled approximately $1.2 trillion in 2014. The successor agreement did not change the geography. Both the freight and the pavement question survived the renegotiation intact, because the constraint at Laredo was never the tariff schedule.
One detail from the district profile shows how far the border logistics chain has been engineered around the delay rather than the distance. Since 2015, Laredo International Airport has offered Mexican pre-clearance, so cargo cleared at the airport is released to the owner on arrival in Mexico without pausing at a Mexican bonded facility. Air cargo destined for Mexico from anywhere in the world can be routed through Laredo to be cleared by Mexican customs. The customs boundary has become relocatable in a way the road has not.
A corridor defined by the cities strung along it
North of Laredo the route becomes something different, which is why arguments about I-35 tend to talk past each other. TxDOT’s current corridor study, running from spring 2025 to autumn 2026, describes the Texas portion as approximately 590 miles from the Oklahoma state line to the international border, carrying roughly four to 10 main lanes plus frontage roads through urban and metropolitan areas, with nearly half of the state’s population living and working along it. The 2016 plan gives the full route as 1,568 miles from Laredo to Duluth, Minnesota, of which approximately 588 miles are in Texas including I-35 East and West through Dallas and Fort Worth, and describes it as the only Interstate connecting Mexico and Canada through the U.S. heartland.
The growth figures behind the state’s planning are worth stating in full because they are the case for every project on the corridor. In 2014 almost 40 percent of Texans and over 40 percent of Texas jobs were located in the 21 counties along I-35. The population of those counties is projected to rise from 9.7 million in 2010 to 17.7 million by 2040, an increase of approximately 82 percent. Employment along the corridor grew from 4,071,102 jobs in 2005 to 4,749,402 in 2014, and is projected to reach 8,117,273 by 2040. Some sections were already carrying over 200,000 vehicles a day when the plan was written.
A corridor with that profile is not a freight facility that also happens to carry commuters. It is a commuter facility that also happens to carry the country’s busiest land border. Every capacity argument on I-35 is a contest between those two functions for the same lane.
Two truck shares, two denominators
The corridor plan contains two statements about how much of I-35’s traffic is trucks, and they do not obviously agree. Citing the state’s 2014 roadway inventory, it reports that trucks accounted for approximately 17 percent of average daily traffic on I-35 in 2014. A later section states that the percentage of total vehicle miles of travel consisting of truck traffic was higher for I-35, at 30 percent, than for any other Interstate in Texas during the same year.
The denominators are named and they are different, one a count of vehicles and the other a distance measure. The plan never reconciles them, but it contains the material to. Table 4, sourced to the state’s Statewide Analysis Model version 3, tabulates daily vehicle miles of travel on I-35 for 2015 as 42,443,503 by passenger automobile and 8,412,102 by commercial truck out of 50,855,605, and it prints the resulting share on its own row: 16.5 percent in 2015, falling to 14.8 percent by 2040. That sits close to the 17 percent of average daily traffic, not to 30.
The 30 percent belongs elsewhere in the same document. Its executive summary states that I-35 holds approximately 18 percent of the total lane miles of the Texas Interstate system but will account for over 30 percent of total VMT on that system in 2040, and the later section restates it as travel on I-35 continuing to account for over 30 percent of total VMT and truck VMT on Texas Interstate facilities in 2040. Read against Table 4 in section 3.5 of the same plan, the sentence offering 30 percent as trucks’ share of I-35 is best read as a drafting error. The discrepancy is resolvable, which is worth saying because both halves are still quoted. The general problem of matching a truck figure to its base recurs throughout freight data, and is treated in what makes a freight corridor important.
What the plan is unambiguous about is direction. Between 2015 and 2040 it forecasts vehicle miles of travel during the morning peak, defined as 6:30 to 8:30 am, to rise 58 percent across the corridor, with 55 percent on urban sections and 65 percent on rural ones. Commercial truck vehicle miles are forecast to rise 46 percent by 2040, a growth rate of approximately 1.5 percent a year.
Austin, measured twice, twelve years apart
Congestion on I-35 has one location that appears in the national record repeatedly. The 2016 corridor plan reports, citing the American Transportation Research Institute, that two of the 100 most congested freight locations in the United States in 2014 were within the Texas portion of I-35, and that I-35 through downtown Austin was listed as the 16th most congested location for freight in the country.
ATRI’s 2026 ranking places Austin’s I-35 at 51, with an average truck speed of 31.4 mph, a peak-period average of 21.7 mph and a non-peak average of 35.0 mph. It is tempting to read a fall from 16 to 51 as improvement and the temptation should be resisted. The 2026 analysis evaluates more than 325 locations using 2025 truck GPS data, and both the location set and the algorithm have changed over twelve years. What the two readings jointly support is that the same segment has been in the national top tier of freight congestion for more than a decade, and that peak-period trucks on it move at about two-thirds of their own off-peak speed.
The crash record does not average out
Safety is the other half of the state’s case for the corridor and the numbers are specific. Over 2009 to 2013 a total of 70,492 crashes were reported along the Texas portion of I-35, of which 63,457, or 90 percent, occurred in urban areas. The five-year average crash rate per 100 million vehicle miles was 130.98 on urban I-35 against 120.84 for Texas Interstates generally, and 61.32 on rural I-35 against 58.28. Counties with the highest five-year crash rate per mile were Travis at 71.8, Dallas at 69.9 and Bexar at 59.3.
The urban gap is about 8 percent and the rural gap is smaller still. That is a real difference on a corridor this long, and it is also a reminder that I-35’s safety problem is concentrated rather than general. The state’s own crash analysis identified locations with five-year average rates more than 1.5 times the state Interstate average, which is a different and more actionable finding than a corridor-wide rate. The gap between an average and a hotspot decides most measurement arguments in freight infrastructure coverage.
The constraint is vertical
The most concrete freight limitation the plan documents has nothing to do with lanes. Using LIDAR survey data collected in 2012 for the department’s rail division, TxDOT counted 314 bridges along I-35 and sorted them by vertical clearance. There were 128, or 40.8 percent, at less than 16 feet 6 inches, 137, or 43.6 percent, between 16 feet 6 inches and 18 feet 6 inches, and 49, or 15.6 percent, at 18 feet 6 inches and greater.
The two thresholds are not arbitrary. The state’s bridge manual requires a minimum of 16 feet 6 inches over the roadway on all new Interstate overpasses, and the Texas Freight Mobility Plan recommends 18 feet 6 inches. Measured against the recommendation, just over 15 percent of the corridor’s bridges comply. The mechanics of how clearance and load capacity are recorded and enforced sit in bridge inspection and rating, and the wider question of how heavy vehicles set geometry is taken up in how trucking shapes highway design.
Set against that, the money question is almost simple. The plan recommends 42 added-capacity projects representing a funding gap of $25,565,267,408, with $16.7 billion of it, or 65 percent, in near-term projects anticipated for completion by 2025, and district shares running from $645 million in Wichita Falls to $7,547,780,195 in Dallas and $3,343,000,000 in Laredo. Widening buys capacity. It does not raise a single overpass. A corridor can be brought to six lanes end to end, as the plan’s development strategy contemplates, and still refuse an 18-foot load at 128 separate structures.