Aiming to ease traffic flow and improve safety, the Texas Department of Transportation (TxDOT) is reconfiguring interchanges in a growing San Antonio community.

"The overall purpose of the project is to address the congestion in this area," says Josh Donat, a Public Information Officer with TxDOT. "Northwest Bexar County is one of the faster growing regions in this area. There are a lot of folks who use these roads."

By reducing congestion, the intersection improvement also should improve safety through operational changes in the configuration of the ramps.

"We want to keep the traffic flow going, because we do not want drivers stopping at the intersections too often," says Carlos Arcila, the TxDOT Engineer for the project. "This configuration will give people ways to get away from the traffic."

Major Area Growth

According to the U.S. Census Bureau, San Antonio's population grew by 12.4 percent from 2010 to 2016. The area is near Lackland Air Force Base, a stimulus for much of the defense industry growth in the area. Several new technological, cybersecurity and medical businesses have come into the region.

"Lackland tends to drive the economy in this portion of town," Donat reports. "Most of the people I see moving in are Department of Defense contractors, medical professionals or in the financial sector. There are a lot of good reasons to move to San Antonio, and that growth has to go somewhere."

The school district in the area has added elementary, junior and high schools. It is the fourth largest district in the state.

"The parents of those kids are driving though this intersection," Donat says. "That is key to remember."

Currently traffic on I-410 is about 197,000 vehicles per day, with that projected to increase to 289,600 by 2036. On U.S. Highway 90, traffic counts are 81,354 daily with an anticipated increase to 126,800 by 2036, and on Texas 151, current traffic is nearing 100,000 vehicles daily, with a projected increase to 155,200.

New Ramp Alignments

This $82 million phase of the project will add to direct connectors: from eastbound Texas 151 to northbound I-410 and southbound I-410 to westbound Texas 151. The project includes adding lanes to I-410 to make it four lanes in each direction between Texas 151 and U.S. 90.

"This is one of several projects we have in this region of San Antonio and Bexar County, and it is a big one," Donat says.

The intersection will feature Super X ramp alignments. The exit ramp is well in advance of the cross street and the entrance ramp immediately after.

"The advantage the Super X provides is to moves the congestion or queue at the cross streets to the frontage roads, which ordinarily would back up to the mainline highway," Donat says "It moves the queue down onto the frontage road and frees up space for traffic moving onto to mainline."

Additionally cars can exit off onto frontage roads, effectively making it an auxiliary lane to the mainline. Traffic could exit, run along the frontage road and then get on the expressway again, without stopping at a signalized intersection. Traffic on the frontage roads flows at about 45 mph, but if the interstate is slowly crawling along at 25 mph, drivers will gain ground on the frontage roads.

"The design allows for it, and some engineers want people to be doing that, not everyone or it won't work anymore," Donat says.  

The connectors are elevated, with overpasses at four cross streets. Those overpasses are being widened, adding a lane to improve capacity. Some of the girders are steel and some are concrete. The curved girders are steel to enhance construction.

Work Progresses with Interesting Concerns

Arcila indicates the bridge work and retaining wall work has progressed well and according to plan. The department is careful in monitoring the water quality at Leon Creek.

"The contractor is getting everything done," Arcila says.

Williams Brothers Construction of Houston began work on the project in fall 2015, with completion expected in summer 2018. The company is using GPS total stations for offsets, elevations, grading and paving.

"Williams Brothers has provided simultaneous work that some other contractors would not be able to do," Donat says.

An interesting component of the project has been concerns by the Southwest Research Institute who expressed concerns about contractors being able to see over the tree line into the institute. The institute does work for the federal government, prompting security concerns. Initially, the design engineers had not realized the seriousness of the institute's worries but quickly put into place mechanisms to address those concerns.

"We did a lot of coordination with the institute to let them know where we were coming from," Arcila says. "We did not take them by surprise."

Looking to the future, the department will likely install visual barrier walls to ensure privacy to the institute.

Future I-410 Work

TxDOT also is reconfiguring the I-410 and U.S. 90 interchange, adding direct connectors from eastbound U.S. 90 to northbound I-410 and southbound 410 to westbound U.S. 90. Williams Brothers also received that contract.

The department bundled the two projects for environmental studies and federal clearances. However, TxDOT separated the projects due to funding. No additional right-of-way was required for the current project. And there were no disproportionately high or adverse effects on minority or low-income populations. Additionally, the work did not affect historical or archeological resources, air quality, wetlands, or federally listed species.  Moving forward, additional work is planned to address access eastbound 151 to southbound I-410 and northbound I-410 to westbound 151. Currently, that work is scheduled for 2021.

 "We are proud of the changes we are doing to this side of town," Arcila says. "The businesses are growing quickly, and it was necessary to come up with projects to help them. It is going to be good."