Two major interstates cross here and two loops offer a way round. The crossing itself is manageable — it is the run north to Austin that hurts.
The junction
I-35 runs northeast to southwest — Dallas and Austin toward Laredo. I-10 runs east to west — Houston toward El Paso. I-37 runs southeast toward Corpus Christi.
Loop 410 is the inner ring. Loop 1604 is the outer ring.
The two loops
Loop 410 circles closer to the centre and carries substantial local traffic. It is useful but it is not a quiet road.
Loop 1604 is well outside the city and is generally the better through-route, especially at peak. More miles, fewer minutes.
The rule, as in Houston: the further out you go, the better the trade at peak. Off-peak, the direct route through is fine.
The I-35 problem north of the city
Worth knowing if you are heading toward Austin.
I-35 between San Antonio and Austin is one of the most consistently congested intercity stretches in Texas, particularly around New Braunfels and San Marcos. The corridor has grown enormously and the road has not kept pace.
TxDOT and the Texas A&M Transportation Institute publish an annual ranking of the state's 100 most congested segments, and stretches of this corridor appear on it regularly.
If you are driving San Antonio to Austin, that 80-mile run deserves more planning than the San Antonio crossing itself. Off-peak makes a substantial difference.
Timing
| Crossing time | What to expect |
|---|---|
| Before 6:30 a.m. | Clear |
| 7:00 – 9:00 a.m. | Morning peak |
| 10:00 a.m. – 3:00 p.m. | Best window |
| 3:30 – 6:30 p.m. | Worst window |
| After 6:30 p.m. | Clearing |
Fiesta San Antonio, a large citywide festival in April, affects central traffic significantly for over a week. Check the dates if you are crossing then.
Weather
Flash flooding is the serious hazard. Central Texas sits in what is sometimes called Flash Flood Alley — the terrain and rainfall patterns combine to produce fast, dangerous flooding. Low water crossings fill in minutes.
Never drive into standing water. Depth is impossible to judge and the road underneath may be gone.
Spring severe weather, March to June — thunderstorms, hail, sudden crosswinds.
Summer heat is sustained and drives breakdowns. If you are continuing west on I-10 toward El Paso, that is a long, hot, sparse stretch that deserves fuel and water planning.
Winter ice is rare and disproportionately disruptive.
If you are stopping
Texas is one of the most permissive states for rest area stops — roughly 24 hours, and widely regarded as among the most truck-friendly in the country. Camping is still prohibited.
Services are plentiful on both loops and at the interstate interchanges.
Before the west Texas run: if you are heading out on I-10 toward El Paso, fuel and provision here. Services thin out considerably and the stretch is long.
Continuing on?
Northeast on I-35: Austin, about 80 miles — and the congested stretch described above. Then Waco and Dallas–Fort Worth. Southwest on I-35: Laredo and the border. East on I-10: Houston, about 200 miles. West on I-10: the long run to El Paso — around 550 miles, sparse and hot. Southeast on I-37: Corpus Christi.
Before you drive
San Antonio is an easy crossing with a hard road attached to it. The Austin run is where the planning pays.
BoardSpy watches the loops and the I-35 corridor north, with live weather including the flash flood conditions that make central Texas different.
Related drive-through guides
Along shared corridors: best time to drive through Houston · best time to drive through Dallas–Fort Worth · best time to drive through Phoenix.
Frequently asked questions
What is the best time to drive through San Antonio?
Between 10:00 a.m. and 3:00 p.m., or after 6:30 p.m. Avoid 7:00 to 9:00 a.m. and 3:30 to 6:30 p.m.
Should I take Loop 410 or Loop 1604?
Loop 1604 is the outer ring and generally the better choice for through-traffic, particularly at peak. Loop 410 is the inner ring and carries substantial local traffic. The further out you go, the more miles and the fewer minutes.
How bad is I-35 between San Antonio and Austin?
It is one of the most consistently congested intercity stretches in Texas, particularly around New Braunfels and San Marcos. TxDOT's annual congestion ranking has repeatedly named segments of it among the state's worst.