What Would the Southwest Connection Cost?

A plain-language cost guide for Dripping Springs / Hays County residents, updated to the new 2026 proposed route. Planning-level estimate in mid-2026 dollars. Construction is not funded.

The ~$250 million figure is a public yardstick from local comps and TxDOT bridge unit costs on the new 2026 alignment (~7.2 miles). It will move when engineers lock spans and right-of-way. What is funded so far is design: about $750K (2019 K Friese study) plus a $2.99M Structurepoint design contract (December 2025) — not building the road.

At a glance

• Mid all-in (7.2 mi): about $252 million

• Planning range: about $146–$443 million

• Per mile (mid): about $35 million

• Construction status: not funded

The short answer

If Hays County built the corridor from US 290 to RM 12 — about 7.2 miles of new four-lane divided road with bike/pedestrian space, six Onion Creek / valley bridges, and a roundabout at Mt Gainor (plus the separate RM 12/150 project) — a planning-level all-in cost lands near $250 million (~$35 million per mile), with a planning range of about $146–$443 million.

That is a yardstick built from local projects you can look up, plus statewide bridge costs. The new route is shorter than the 2021 preliminary centerline and drops two corridor roundabouts and one short bridge.

Corridor map and elevation profile

Design already under contract

These pay for studies and plans — not asphalt, bridges, or right-of-way for construction.

• K Friese + Associates — $750,000 — Dec 2019 — Preliminary engineering + public involvement (RM 12 → US 290)

• American Structurepoint — $2,986,101 — Dec 2025 — Design US 290 → RM 12 (schematic through PS&E via work authorizations)

Baseline: Darden Hill Phase 2

The cleanest local comparison is already on the county’s books: Darden Hill / CR 162 Phase 2 (Sawyer Ranch roundabout to RM 1826).

• 1.7 miles of four-lane divided road

• Published cost: $51.793 million

• Includes construction, utilities, right-of-way, design, and CEI

• All-in: about $30.5 million per mile

Simple math: 7.2 miles × $30.5M ≈ $220 million for roadway-class work alone. Our full-project mid (~$250M, ~$35M per mile) sits a little higher — expected for a greenfield alignment with six bridges, contributing-zone drainage, and new right-of-way.

Baseline: Bridges

The new centerline and elevation profile show six major valley or floodplain crossings (B1–B6). Planning spans come from DEM valley width (~15 ft rise). Cost uses TxDOT FY 2025 ~$135/sf × ~90 ft deck + approaches. Six majors mid ≈ $32 million (B2 half embankment).

• B1 — Onion Creek main floodplain — ~520 ft — ~$7.0M

• B2 — East trib / draw (half bridge, half fill) — ~420 ft — ~$5.9M

• B3 — Near Mt Gainor (west) — ~280 ft — ~$4.3M

• B4 — Mid-corridor valley — ~260 ft — ~$4.0M

• B5 — West mid-corridor valley — ~610 ft — ~$8.2M

• B6 — Near US 290 approach — ~200 ft — ~$3.0M

Local checks: Creek Rd CR190 Onion ~$1.5–1.6M floor; Cole Springs (Buda) ~$7.6M package.

Baseline: Roundabouts

County preference on this corridor has been roundabouts at major local intersections. The new alignment would require one new roundabout at Mount Gainor Rd. as well as a new tie-in to US 290.

• R1 — RM 12 / RM 150 — ~$9M — separate county project (not inside the ~$250M corridor total)

• R2 — Mt Gainor Rd — ~$4M

• US 290 tie-in — ~$2.5M

Corridor intersections mid ≈ $6.5 million.

Putting the pieces together (mid case)

• Roadway + drainage + paving + earthwork + bike/ped + utilities + mobilization — ~$110M

• Bridges & large culverts — ~$35M

• Intersections (corridor roundabouts + tie-ins) — ~$7M

• Contingency + design + CEI + ROW + env — ~$100M

• All-in mid — ~$252M — about $35M per mile

Independent planning-level estimate for public discussion (new 2026 alignment). Not a Hays County engineer’s estimate.

Sources

• Hays County minutes — Dec 10, 2019 (K Friese PSA $750,000): https://www.egovlink.com/public_documents300/hayscounty/published_documents/court_minutes_archive/2019/12-10-2019.pdf

• Hays County agenda packet — Dec 16, 2025 (Structurepoint design cap $2,986,101): https://public.destinyhosted.com/hayscdocs/2025/CC/20251216_115/AGENDApacket__12-16-25_0534_115.pdf

• Hays County Bonds — Darden Hill Phase 2 ($51.793M; 1.7 mi): https://hayscountybonds.com/darden-hill-phase-2

• Hays County Roads — Southwest Connection: https://www.hayscoroads.com/dripping-springs-sw-connection

• Hays County Roads — RM 150 at RM 12: https://www.hayscoroads.com/rm12-rm150-intersection

• TxDOT FY 2025 Bridge Unit Costs (~$135/sf average): https://www.txdot.gov/content/dam/docs/division/brg/publications/unit-costs-2025.pdf