A discussion paper offers Sonoma County more air connectivity without a bigger airport

Sonoma County is planning fifteen years of airport growth. Apron construction is under way at Charles M. Schulz–Sonoma County Airport, consultants are coordinating some thirteen potential projects around the terminal, and the phasing and funding of many of them remain undetermined. The reason offered for all of it is connectivity: more destinations, more convenient schedules, less driving to San Francisco or Oakland.

A discussion paper submitted to the county on August 31 proposes a different way of getting there. It went to the General Plan Sonoma team at Permit Sonoma as the last of four requests — the first three concerned how the successor plan should record and handle that growth — and what it asks the county to study is a facility that would handle passengers but no aircraft.

The paper separates connectivity from aircraft

The proposal is a landside satellite terminal on the US-101 corridor south of the airport. Passengers would check in there, check their bags, and clear TSA security, then board a secure bus to Oakland San Francisco Bay Airport (OAK), arriving on the secure side without being screened again. Sonoma County would be connected to the route network OAK already has, rather than reproducing that network at STS one destination at a time.

The facility would not be a certificated airport. It would host no aircraft operations, would not alter the airport's operating certificate, and would not be built with airport improvement funds.

Where it would go is left open. The paper uses Rohnert Park illustratively and says candidate sites should be compared on their merits; what it treats as necessary is a corridor location south of STS, large enough, with freeway access and suitable zoning. One preference is weighted heavily. A site walkable from a SMART platform — better still, one built around it — would allow car-free access and extend the terminal's reach up the rail line. The airport can't have that: its SMART station sits about a mile from the terminal, because the rail alignment and the runway geometry were each fixed by something else. A satellite terminal can be sited for transit integration instead. Land next to a platform is scarce, so the paper doesn't assume it, and a site without rail would forfeit part of the advantage rather than defeat the idea.

The outbound half of the mechanism is already running. TSA, Massport, and the motorcoach operator Landline opened a remote terminal at Framingham, Massachusetts, about 25 miles from Boston Logan, in June 2026. It carried its 10,000th passenger within two months, and the pilot has been extended into early 2027.

The paper is careful about what that proves. Framingham establishes that TSA can approve off-airport screening and secure transport into an airport's sterile area. It doesn't establish that TSA would approve a California facility, and it doesn't demonstrate the inbound version — arriving passengers and their bags continuing to Sonoma County inside a single airline itinerary — which would need its own airline and regulatory design.

What follows from the mechanism is the paper's actual argument. The county's growth case treats "more air service" and "more aircraft over Sonoma County" as one proposition. They are two. What residents are said to want is to reach places, and a terminal with a bus lane delivers that without adding a departure to the runway.

The first passengers are already driving to Oakland

A satellite terminal doesn't have to persuade anyone to want something different. Its most plausible starting market is people already making the journey.

The county has measured that population. A passenger leakage study by Crawford, Murphy & Tilly, presented to the Aviation Commission on November 18, 2021, found demand of 7,211 passengers a day each way within the airport's catchment, and that only about 7 percent of them used STS. The rest largely drove to San Francisco or Oakland, for a destination, a fare, or a schedule STS didn't offer.

STS has grown strongly since, and the paper concedes that before making anything of the figure. Measured against the same catchment, the 780,637 passengers STS carried in 2025 come to roughly 15 percent of it — about double the earlier share — and 2026 is running higher again. The 15 percent is the author's own calculation, and it assumes a catchment that hasn't itself grown, which makes it an upper bound. The underlying study also counts two different populations together: departing residents, and the visitors who make up 56 percent of catchment travel and whose journeys begin somewhere else. Taken at its most flattering to the airport, the number still leaves something like five of every six catchment passengers reaching the Bay Area's major airports by road.

Those drivers are who a corridor terminal would compete for, and what it would compete against is a long drive, airport parking, and sole responsibility for arriving on time. Whether it wins them is a question about the cost and reliability of the ground connection, not about persuading satisfied STS passengers to give something up. Any effect on demand at STS would follow from what passengers and airlines chose to do, which is not something the paper proposes to arrange.

Federal obligations require the county to operate the airport, not to expand it

Federal grant assurances constrain what Sonoma County does with the airport it owns. The county must operate and maintain STS in safe and serviceable condition, keep it available for public use on reasonable terms, refrain from granting exclusive rights, and keep an approved layout plan current for physical changes there. Those are obligations about the airport, and none of them requires the county to make it bigger.

A separate landside facility sits outside that framework. The one direct contact point is money: airport revenue can't be diverted to off-airport purposes, so a satellite terminal would have to be funded as a county transportation project in its own right. Within that limit, the choice between expanding STS and building something else is a question of county transportation policy rather than federal obligation.

The paper asks the county to study the idea, not to build it

The cover says what the document is. It proposes no capital project and requests no construction funding. What it asks for is a preliminary feasibility assessment, and exploratory discussions among the county, potential host jurisdictions, the Port of Oakland, TSA, potential airline partners, and a qualified ground-transportation operator.

Section 8 sets out what such an assessment would have to answer, and the list isn't a short one. Four questions gate everything else: what conditions TSA would impose, whether the Port of Oakland and at least one airline would take part, who would own, operate, and pay for the terminal and the bus service, and what an initial operating scope would look like. Below those sit the design of the service itself — through-ticketing, baggage, and who carries the loss when the bus is late — along with site selection, the size of the outbound and visitor markets, journey-time reliability on the corridor, the effect on STS service and jobs, and a like-for-like comparison of capital cost, embodied carbon, and trip-level emissions against the program the airport is already planning.

The submission makes the ask concrete in planning terms: that the alternative be evaluated during policy development, and that the county consider whether the successor plan should carry an implementation program calling for that feasibility work.

That framing is the point. Approving a project is a large decision, made slowly and defensively. Commissioning a study is a small one.

The alternative is now in front of the process that would weigh it

The General Plan update is where Sonoma County settles its air transportation policy for the life of the successor plan. Until now, the only future on the table has been a larger airport in the same place.

There is now a second option in the file, with its mechanism described, its precedent named, its initial market documented by the county's own study, and its unanswered questions listed by the person proposing it. Whether it would work is what a feasibility study is for. Whether it gets one is a decision the county now has to make on the record rather than by default.

The discussion paper is archived on Sonoma Air Record: Satellite terminal discussion paper. The fifteen-year program and the review the county has no record of conducting are covered separately in Sonoma County's airport crossed a threshold requiring Board review seven years ago.

Written in collaboration with Claude (Anthropic).