Maryland Gov. Larry Hogan (R). (Patrick Semansky/AP)

The Washington region — current population roughly 5.4 million, by the Council of Governments’ estimate — is projected to grow by 1.5 million people over the coming quarter- century. Faced with that influx, public officials don’t have the luxury to engage in theological debate about the comparative benefits of transit vs. roads vs. new technology. If the region is to remain livable, prosperous and mobile, it will need more of all of the above.

That’s why Maryland Gov. Larry Hogan’s recent big-ticket suburban transportation proposalshundreds of millions of dollars to rescue Metro, and $9 billion to add dozens of miles of toll lanes to the Beltway, Interstate 270 and the Baltimore- Washington Parkway — are a good starting point. His ideas can and will be criticized as politically opportunistic, fiscally suspect and practically flawed. Yet without being shoved to the top of the regional agenda — which Mr. Hogan has achieved by sheer audacity — the region’s transportation system will remain stuck in its current state of alarming inadequacy.

The widening of those highways — three crucial arteries for hundreds of thousands of Maryland commuters — is a bold suggestion, measured by scale and dollars. A Republican, Mr. Hogan insists that taxpayers will be spared any cost — that private-sector partners can be found to finance, build, operate and maintain four new tolled lanes along Maryland’s portion of the Beltway, and on I-270 from the Beltway to Frederick. The revenue from those projects would pay to widen the parkway with new tolled lanes, whose upgrade would be handled by the state, the governor said.

The idea that this is all “free” for taxpayers is implausible, to say the least. For one thing, the new lanes, whose tolls would be set minute by minute according to demand, would certainly be expensive for commuters who drive on them, most of them Maryland taxpayers. Then there are the fine points — for instance, would the state have any financial exposure if toll revenue failed to meet projections?

And don’t imagine that all those new Lexus lanes would ease traffic much in the existing, non-tolled lanes. By a pattern known to planners as “induced demand,” more roads have a way of attracting more cars to use them.

For that reason, environmentalists, who hold sway in the Democrat-dominated legislature in Annapolis, are no fans of road-building. Yet it is folly to think that the additional people who live in this region in 2045 will be using buses, bikes and subways exclusively. The name of the game is capacity, and without much more of it, including road capacity, Maryland will be a worse place to live, and its ability to compete economically will be diminished. After all, suburban Virginia has already done much of what Mr. Hogan is proposing, and the construction of toll lanes continues there at a robust pace.

Democrats, including those hoping to challenge Mr. Hogan in next year’s gubernatorial election, scoff at his proposals as a brazen play for suburban votes. Homes and parks would have to be razed to make way for toll lanes, they say, and the Metro proposal is going nowhere for now.

Fine. Then what’s their idea for absorbing 1.5 million new people, or even Maryland’s share of that flood? We’re not hearing anyone propose huge new taxes. Mr. Hogan has done what executives are supposed to do: get the ball rolling.