The South Congress Avenue Bridge in Austin, Texas spans Lady Bird Lake. It is the fourth iteration of a bridge at that site, and is home to the largest summer colony of Mexican free-tailed bats in the world.
Prior to a fixed bridge, three ferries operated across the Colorado River in Austin: Grumbles' on Barton Creek, Stone's on Waller Creek and Swisher's at Congress Avenue.(2) The first bridge to cross the Colorado was a tolled pontoon bridge at Brazos Street that was completed in 1869. It was destroyed in a flood just eleven months later and the three ferries resumed operations. But the death of Elizabeth Boyd Swisher in 1875 ended one of the three ferries.
A permanent, tolled wooden bridge was completed in that year (2) at a cost of $80,000. An additional $20,000 was spent to macadamize dykes across the low land and to install a culvert over Bouldin Branch.
The Swishers' owned significant acreage south of the Colorado River for their family farm along the San Antonio Road. Two years after the wooden bridge was completed, the family subdivided 23 acres of their farm for development. Acknowledging the potential for growth in the southern reaches of Austin, Swisher allocated an 120-foot right-of-way through the center of the 23 acres, with the new roadway laid out in a direct line with Congress Avenue on the north side of the river.(2)
In 1883, a 120-foot span of the wooden bridge collapsed under the weight of a herd of cattle.(2) Seeing the need for a stronger crossing, the wooden bridge was replaced with an iron crossing constructed by the King Bridge Company of Cleveland, Ohio that was opened on January 22, 1884 at a cost of $74,000. The span, all privately funded and designed by C.Q. Horton, was high enough to allow for the highest stage of flooding along the Colorado. It was also the first bridge across the Colorado that was not tolled. The Travis County Road and Bridge Company and the city of Austin purchased the bridge on June 18, 1886.
But by 1891, the Travis County Road and Bridge Company refused to accept future maintenance responsibility of the crossing, and negotiated an agreement with the city for it to take over the bridge's operation. The city completed repairs in 1892 and 1897 - the latter which required reflooring the bridge, a task that took until 1901 to complete. The iron truss was repainted a year later.
In 1907, a group of southern Austin businessmen began discussions on replacing the iron bridge due to frequent congestion on the narrow crossing.(2) Plans for a new concrete arch bridge was formalized and a bond was issued in the following year. During construction, the old iron truss was shifted onto temporary piers while the new bridge was built in its place. The new crossing, which included a 50-foot wide span with two interurban railway tracks and overhanging sidewalks,(2) was completed on April 3, 1910 at a cost of $208,950.10.
Sections of the old iron bridge were reused in 1915 and 1922 to rebuild the Moore's Crossing Bridge over Onion Creek.(2)
In 1956, the South Congress Avenue Bridge's roadway was widened to four lanes to accomodate more automobile traffic.(2) It was widened and rehabilitated again in 1980.
Today, the bridge is home to the world's largest urban bat colony consisting of Mexican free-tailed bats.(1) The bats, numbering between 750,000 and 1.5 million, reside under the bridge deck in gaps between the concrete components. The bats are migratory, spending the summers in Austin and winters in Mexico. At dusk, the bats emerge and fly across Lady Bird Lake towards the east for food. The daily ritual attracts as many as 100,000 tourists annually, resulting in an economic impact of $7.9 million per year.
- Designation: South Congress Avenue
- Type: Truss
- Main Span Length: 160 feet
- Total Length: 910 feet
- Width: 18 feet
- Truss Height: 27 feet
- Vertical Clearance Below Bridge: 45 feet
- Designation: South Congress Avenue
- Type: Arch
- Main Span Length: 119 feet
- Total Length: 950 feet
- Deck Width: 60 feet