In a project similar to the renovation of the Interstate 25 Escondida interchange, the New Mexico Department of Transportation is reevaluating the design of the aging San Antonio interchange.
Last Thursday, a second public meeting was held via Zoom with representatives from NMDOT, HDR Engineering, and Molzen-Corbin Architects.
As outlined in a May 5 Chieftain article, the interchange was found to be deficient in acceleration and merge lanes for entrance ramps, roadway superelevation geometry, and drainage elements.
“All five bridge structures in the study are reaching the end of their design life,” said Mark Salazar, DOT District 1 Project Development Engineer. “Those 50-plus years old structures are currently showing signs of dilapidation and disrepair.”
Citing results from the first public meeting in November, the presenters said most often mentioned by the public were drivers’ safety with the existing roadway, ramp geometry concerns, and concerns about the northbound on-ramp.
Flood control was also a significant concern and is a project priority.
The proposed drainage plans aim to ensure proper drainage through the interchange and mitigate the risk of flooding down Highway 380.
Three build alternatives were presented, ranging from a minimal adjustment of northbound and southbound ramp improvements to a complete overhaul of the interchange, including the removal of obsolete bridges.
Alternative 1, as presented, would involve enhancing the existing roadway geometry, eliminating the northbound and southbound entrance ramp issues, replacing I-25 bridges, and improving the drainage conveyance of Walnut Creek. Disadvantages are potential flood conditions involving the concrete box culvert crossing at Walnut Creek, which would remain. It would be the least costly.
Alternative 2 would create a tight diamond interchange geometry and match the existing Highway 380 alignment. This alternative would remove the bridge on the southbound entrance ramp reducing the risk of flooding by removing the structure from the waterway, and replacing the I-25 bridges over Walnut Creek to improve the drainage conveyance of Walnut Creek. This alternative would require temporary closures of Highway 380 during the construction of the bridges.
Alternative 3 would also create a tight diamond interchange geometry but also adjust Highway 380’s alignment. This involves the removal and replacement of bridges listed in Alternative 2. This alternative does not require Highway 380 closures during construction, although additional right-of-ways will be necessary. There will be an increased construction cost compared to Alternative 1 and 2.
It was pointed out that Alternative 3 would have the most negligible impact on closures, but construction would last more than a year.
The comment period will end on June 17, 2023.
The project’s next phase involves environmental documentation, followed by a third public meeting yet to be scheduled. The final phase will produce a preliminary design.
The three alternatives: