If built, the SH 45 SW extension from FM 1626 to I-35 would mostly serve commuters in southern Travis County and northern Hays County as an alternative to local routes.

“There’s an element of demand already at that location, and by completing the corridor you’re only seeing a small diversion of additional trips that were previously using other routes,” said Jonathan Avner, a senior project planner who was contracted through CDM Smith to analyze the traffic impacts of building the extension.

In October, construction is scheduled to begin on SH 45 SW from south MoPac in Travis County to FM 1626 in northern Hays County. An extension of SH 45 SW from FM 1626 to I-35 is included in the Capital Area Metropolitan Planning Organization's 2040 long-range transportation plan.

CAMPO consulted CDM Smith for the traffic demand modeling analysis to look at who would use SH 45 SW, the trip origins and destinations of those users and how building SH 45 SW would affect other roads such as MoPac, FM 1626, I-35 and Brodie Lane.

In a presentation April 4 to the CAMPO policy board, Avner said the analysis showed the extension would cause a traffic decrease by 18 percent on FM 1626 south of the proposed interchange with SH 45 SW and increase traffic by 38 percent on SH 45 SE, which is east of I-35, according to CDM’s data.

On I-35 south of SH 45 SE, traffic would decrease by 3 percent and decrease by 2 percent south of Slaughter Lane. On MoPac, traffic would increase by 4 percent north of Slaughter and increase by 11 percent, or almost 5,000 vehicles, north of SH 45 SW, according to the data. On SH 45 SW, traffic would increase by 22 percent.

Traffic would be heaviest on the eastbound SH 45 SW extension in the morning because of commuter traffic and vice versa in the afternoon, Avner said.

“The commuting path in the morning is actually toward I-35 when a lot of people would expect that it’s the reverse that you would see traffic from [northbound] I-35,” he said “We’re actually seeing the corridor [would serve] a lot of the population in Hays County getting to I-35 and destinations along the corridor.”

Avner said CDM’s results are consistent with those found by Stantec, which had completed a traffic analysis study on the extension using data from CAMPO’s 2035 long-range plan.

Overall, CDM’s analysis indicated traffic would increase on SH 45 SW but the impacts beyond that road would be minimal, he said.

“The traffic using the corridor seems to be local in nature … [and] it’s providing some improvement to some those travelers,” Avner said. “Without the 45 extension in place the traffic is already reaching its destinations using 1626 and Loop 1 and then some eastbound and westbound arterial systems.”