State Highway 3-A Bridge at Plum Creek

The State Highway 3-A Bridge at Plum Creek, built from 1930 to 1931, is significant for embodying the defining characteristics of a THD truss bridge. As such, the bridge meets National Register Criterion in the area of Engineering at a state level of significance.

The Plum Creek bridge was built on a segment of highway shared by two routes, SH 3-A and SH 29, that traversed Caldwell County. The segment originated in Luling where the two routes met, proceeding southeasterly for four miles before dividing just north of the Gonzales County line. SH 3-A (now US 90) continued its course eastward across the southern tip of Caldwell County. This route was the northern branch of former SH 3, the Southern National Highway, which linked Del Rio, San Antonio, Houston, Beaumont, and Orange. SH 3 split into two branches in Central Texas, between Seguin (Guadalupe County) and Waelder (in eastern Gonzales County). The primary route, SH 3, took a southerly course through Gonzales while the northern route, SH 3-A, passed through Luling before rejoining the primary route in Waelder. By the late 1930s, SH 3-A replaced SH 3 as the primary route and was designated US 90. This segment of highway also served as part of SH 29 (now US 183). SH 29, also known as the Middle Buster Highway, ran north-to-south from Austin through Lockhart and Luling, where it briefly joined SH 3-A, and then continued on through Victoria to Port O'Connor on the Gulf Coast. By 1952, SH 29 had been improved and redesignated US 183, and the shared segment of highway in southern Caldwell County was designated US 90/US 183.

The Plum Creek bridge was built as part of a larger THD project to reconstruct the eastern half of SH 3-A on a new location. The new route from Luling to Waelder would allow for improved crossings with better stormwater drainage and less possibility of bridge flooding. In addition to the construction of the truss bridge, the project included new roadway grading and concrete drainage structures. THD prepared the plans and because it was a federal aid project, the Bureau of Public Roads (BPR) reviewed and approved them. The THD resident engineer in Luling supervised the construction, which engineers from both THD and BPR inspected.

THD bridge engineers chose the T22-120 design for the truss span of the Plum Creek bridge. The T22-120 is one of 25 THD standard designs that the Bridge Division developed for Parker through truss spans and one of only 11 of these designs represented by bridges in Texas today. The T22-120 was first designed about 1930; a second version was completed in 1932. The Plum Creek bridge is the only surviving example of the T22-120 standard design, conforming to the first version which called for the use of horizontal bracing to prevent buckling of tall vertical members. The design was improved in the second version, eliminating the need for horizontal bracing despite an increase in truss height. Only one other THD standard design, the T22-250, utilized horizontal bracing. The US 69 Bridge at the Red River in Grayson County, built the same year as the Plum Creek bridge, is the only bridge conforming to this standard design. These two bridges are representative of a temporary solution to the potential buckling of vertical members in tall trusses; the problem was subsequently eliminated through the improved design of the vertical members themselves.

The bridge's 38-deck girder approach spans provide a lengthy approach of more than 1,000 feet. Although construction plans for the bridge show paneled concrete entrance railing, the bridge today exhibits shortened Type D railing flared at each entrance. Since no as-built drawings of the bridge exist, it is unclear whether the paneled railing was ever constructed or whether it was later replaced.
The Texas Highway Commission opened bids for the construction of the Plum Creek bridge on July 30, 1930. After reviewing the five bids submitted, the Commission awarded the contract to Grant Williams of Oklahoma City, who submitted the low bid of about $109,000. The contract for the rest of the work on SH 3-A, i.e., roadway grading and concrete drainage structures, was awarded to the Standifer Brothers (address unknown). The Virginia Bridge and Iron Company of Roanoke, Virginia, fabricated the truss span.

Construction of the Plum Creek bridge began on October 9, 1930, and was completed by August 1931. Work on the grading and concrete structures took place between October 1930 and January 1933. During the construction of the bridge, THD engineers judged the piers' timber foundation piling unnecessary, as the soil was stable enough to support a simple spread footing. The total cost of the bridge came to about $114,000. From 1932 to 1934, THD implemented projects to place concrete paving on the same section of SH 3-4, from Luling to Waelder.

In the 1950s, THD implemented two projects affecting the Plum Creek bridge. In 1952, THD maintenance forces shortened the bridge's concrete approach railing. This was done as part of a THD campaign promoting bridge safety initiated by DeWitt C. Greer, then State Highway Engineer. In 1944, he released Administrative Circular 3-44 encouraging districts to shorten Type C and Type D concrete bridge railing. Evidently, the standard railing height of just over 3 feet made bridges appear narrow, causing drivers to veer toward the center of the roadway and sometimes collide. By shortening the railing, the illusion of the narrow bridge relative to the approach roadway was lessened. In addition, the decreased railing height allowed truck overhangs to clear the railings. The retrofit was performed by sawing off the top of each concrete post, removing the upper row of the railing, and casting a new top on each post.
In 1956, THD responded to increasing traffic volumes on US 90/US 183 by constructing a series of concrete slab, girder, and I-beam spans adjacent to the Plum Creek bridge to serve westbound traffic (see Photograph 3). The Plum Creek bridge was then converted into a one-way bridge providing two lanes for eastbound traffic on the route. This configuration lightened the traffic burden on the truss bridge, allowing for its preservation in place.

In 1990, THD maintenance forces performed a structural upgrade to the bridge deck. This entailed placing nine new stringers adjacent to the original stringers which were in an advanced state of deterioration. In addition, construction and expansion joints were routed, cleaned, and sealed.

The deck upgrade modified only the underside of the bridge and did not alter the bridge's original appearance. The amount of new material is minimal and the vast majority of the original structure remains functional. Although the construction of the companion structure has somewhat altered the setting of the truss bridge, as a transportation facility it is compatible with the use of the original bridge and therefore does not significantly compromise its integrity.