There are thirteen business routes of Interstate 35: nine are in Texas, two are in Iowa, and two are in Minnesota.
Texas
Laredo business spur
Business Spur 35 in Laredo, Texas, inventoried by TxDOT as Business Interstate Highway No. 35-A, has a "dangling end", running from the end of the I-35 to the downtown area in Laredo and into Gateway to the Americas International Bridge, continuing south as Mexico Federal Highway 85. The route is long. In Laredo, I-35 Business runs from its junction with I-35 southward along San Bernardo Ave to Houston St; thence westward along Houston St to Salinas Ave; thence southward along Salinas Ave to the U.S. Customs Port-of-Entry; thence northward along Convent Ave to Matamoros St; and thence eastward along Matamoros St to the junction of I-35 and US 83. Travelers going south on I-35 in Laredo can take one of two toll international bridges across the Rio Grande and the Mexican border—straight ahead into Juarez-Lincoln International Bridge, or via I-35 Business through downtown Laredo into Gateway to the Americas International Bridge. This was designated as Texas State Highway Loop 420 on November 5, 1965, but was changed to Business US 83-K on June 21, 1990, but as Business I-35-A on March 26, 1991.
Encinal business loop
Business Loop 35 in Encinal is inventoried by TxDOT as Business Interstate Highway No. 35-B. It is a former alignment of US 81. The route's southern terminus is at northbound I-35 exit #38, just south of the Webb–La Salle county line. It briefly travels westward, crossing under I-35, and then turns north along Main Street, paralleling the Union Pacific Railroad tracks to the west. It has an intersection with SH 44 and turns to the east, concurrent with SH 44, before ending at I-35 exit #39. From January 20, 1977 to June 21, 1990, this route was designated Loop 532, but was signed as a US 81 Business Route.
Cotulla business loop
Business Loop 35 in Cotulla is inventoried by TxDOT as Business Interstate Highway No. 35-C. It is routed along Main Street, which was previously US 81, and connects to I-35 at exits #65 and #69. Within the Cotulla city limits, the route intersects SH 97 and FM 468.
Dilley business loop
Business Loop 35 in Dilley is inventoried by TxDOT as Business Interstate Highway No. 35-D. It is routed along Main Street, which was previously US 81. The route's southern terminus is at I-35 exit #82; it travels northward, paralleling the Union Pacific Railroad tracks to the east. Within the Dilley city limits, the route intersects SH 85 and FM 117 before ending at I-35 exit #86.
Pearsall business loop
Business Loop 35 in Pearsall is inventoried by TxDOT as Business Interstate Highway No. 35-E.
New Braunfels business loop
Business Loop 35 in New Braunfels is inventoried by TxDOT as Business Interstate Highway No. 35-H. The highway is known locally as Elliot Knox Boulevard. The highway was designated on March 26, 1991, with the mileage being transferred from US 81. BL 35-H begins at I-35 exit 185 and briefly runs along Schimdt Avenue, before turning onto Elliot Knox Boulevard approximately north of I-35. The highway runs in a generally east-west direction, passing by many residential areas. Just east of Seguin Avenue, BL 35-H crosses over the Guadalupe River and briefly serves as the frontage road for southbound I-35. The highway turns towards the northeast and has an intersection with SH 46/Loop 337 before running through less developed areas of the town. BL 35-H ends at I-35 exit 190A, near Canyon High School. ;Junction list
Kyle business loop
Business Loop 35 in Kyle is inventoried by TxDOT as Business Interstate Highway No. 35-J. It is the former alignment of US 81 through the city. The route is accessible from southbound I-35 at exit #213, which serves RM 150; the business loop designation begins along the frontage road at the end of the exit ramp. The road travels through Kyle and crosses RM 150 before once again becoming the southbound I-35 frontage road north of mile marker 213.
Round Rock business loop
Business Loop 35 in Round Rock was inventoried by TxDOT as Business Interstate Highway No. 35-L. Commissioned on June 21, 1990, it followed the previous route of US 81 along Mays Street, from Hesters Crossing Road to Old Settlers Boulevard for approximately. The designation was cancelled on February 28, 2013, and the section north of US 79 was transferred to Spur 379. Spur 379 was given to the city of Round Rock on March 26, 2020. From August 1, 1963 to June 21, 1990, the route was designated as Loop 384.
Georgetown business loop
Business Loop 35 was a former business route of I-35 in Georgetown. It was inventoried by TxDOT as Business Interstate Highway No. 35-M. The route was decommissioned on May 25, 2006, with portions being renamed as Spur 26 and Spur 158. From October 15, 1965 to June 21, 1990, the route was designated as Loop 418.
Alvarado business loop
Business Loop 35 in Alvarado is inventoried by TxDOT as Business Interstate Highway No. 35-V. It runs along the former alignment of US 81 along Parkway Drive and is accessible from Interstate 35W at exits #24 and #26B. The section from US 67 to College Street is cosigned as US 67 Bus., though it is not part of that route's official designation. From November 20, 1963 to October 25, 1990, the route was designated as Loop 392.
Sanger business loop
Business Loop 35 in Sanger is inventoried by TxDOT as Business Interstate Highway No. 35-X. The route is a former alignment of US 77 through Sanger, and is accessible from both directions of I-35 at exit #477. The route travels north along 5th Street and crosses FM 455 before ending at the northbound I-35 frontage road near mile marker 479. From November 18, 1960 to December 19, 1991, this route was designated Spur 138. Since March 26, 2009, that route number has been used for an unrelated route in Hunt County.
Iowa
Ames business loop
Business Loop 35 in Ames, Iowa runs between Exits 111 and 113. It begins westbound from Interstate 35 overlapping U.S. Route 30 westbound, then turns north at the interchange with U.S. Route 69 At Lincoln Way, the routes turn west again, only to turn north again at Grand Avenue. BL 35 breaks away from the overlap with US 69 by turning east onto East 13th Street until finally terminating at I-35.
Clear Lake business loop
Business Loop 35 in Clear Lake, Iowa runs between Exits 193 and 194 on Interstate 35. The route begins at Exit 193 where it runs west along Fourth Avenue South, until the intersection with North Eighth Street and turns north. Immediately after a grade crossing with a former Milwaukee Road railroad line, the route makes a right turn overlapping US 18. The route follows US 18 which itself runs parallel to that old Milwaukee Road line until it curves away after North 14th Street. East of North 20th Street, BL 35/US 18 becomes a divided highway. BL 35 ends at Exit 194 on I-35, US 18 turns south in an overlap with I-35, and the road previously carrying both routes becomes US BUS 18 / IA 122.
Minnesota
Faribault business loop
Business Loop 35 in Faribault, Minnesota, begins at the intersection of I-35 and Lyndale Avenue/County State Aid Highway 48 to the intersection with Minnesota State Highway 60 and thence northerly along Minnesota State Highway 21, and terminates at the intersection of I-35 and MN 21. The route travels south to north through the business district of Faribault, a distance of approximately 3 miles.
Albert Lea business loop
Business Loop 35 in Albert Lea, Minnesota, runs along U.S. Route 65 between Exits 8 and 12 on Interstate 35. The route begins at a quarter cloverleaf interchange with Exit 8 and runs northwest along US 65, a four-lane at-grade divided highway. North of Seventh Avenue, the routes curve straight north onto South Broadway Avenue and becomes a two-lane undivided highway. Arriving downtown, the routes intersect Front Street with a level crossing of a railroad line running from the southwest to the northeast corner of that intersection before crossing another railroad line immediately after this intersection. BL 35/US 65 makes a sharp right turn to the east onto Main Street, while in the opposite direction is the southern beginning of MN 13. North Broadway continues from that point towards Fountain Lake Park four blocks north. BL 35/US 65/CHAS 46 runs straight east along a divided highway for a block and a half then begins to curve to the northeast until after it crosses a bridge over the Shell Rock River, then curves back to the east before the bridge over the first railroad line that two of these routes crossed downtown. Halfway between Ulstad and Fenton Avenues the road curves to the northeast again and the divider widens, as frontage roads begin on both sides at Morningside Avenue. East of the intersection with Prospect Avenue, BL 35 and US 65 breaks away from CHAS 46 at a northbound only wye interchange, and has only one last intersection at Sorenson Road and Blake Avenue. BL 35 and US 65 both terminate at a northbound only flyunder interchange with I-35 at Exit 12, which is marked as such southbound.
Business Loop 35 in Pine City, Minnesota, begins at the intersection of I-35 and County State Aid Highway 7 to the intersection with County State Aid Highway 61 and thence northerly along County State Aid Highway 61, parallel to I-35, to the intersection with County State Aid Highway 11. Thence the business route extends westerly along County State Aid Highway 11 and terminates at the intersection of I-35 and County State Aid Highway 11. The route travels south to north through the business district of Pine City, a distance of approximately 3 miles.
