The public face of Maryland’s biggest — and most controversial — transportation projects in recent years is stepping down.

Transportation Secretary Pete K. Rahn said Monday he would resign Jan. 9 to return to New Mexico to be with his wife, Sue, and their two grown children and five grandchildren. She did not move to Maryland when he took the job at the start of the administration of Gov. Larry Hogan (R) in January 2015.

“My wife told me, ‘Come home or don’t bother coming home,’ ” Rahn said.

Rahn, 65, has been the senior policymaker and salesman for most of Hogan’s signature transportation efforts, including building the light-rail Purple Line, investing billions in road and highway improvements across the state, encouraging Elon Musk to pursue a hyperloop beneath the Baltimore-Washington Parkway and launching an effort to add toll lanes to widen the Washington region’s most congested highways.

Rahn will be replaced by Gregory Slater, who oversees the State Highway Administration. In that job, Slater was the lead negotiator for the recently announced deal between Maryland and Virginia to rebuild the American Legion Bridge. He also “spearheaded” Hogan’s plan to use a public-private partnership to install toll lanes on the Capital Beltway and Interstate 270, the governor said in a statement announcing the change.

Rahn’s forceful support for shifting spending from transit to roads, and his flair for blunt, occasionally impolitic language, often led to tangles with Democratic elected officials and activists. He occasionally had to withdraw or soften remarks, such as when the governor’s office said Rahn “misspoke” when he said the state was offering Amazon a “blank check” for transportation improvements to try to lure it to build a second headquarters in Maryland.

Slater, who is described as having a more collaborative style, was expected to have smoother relations with the legislature, local governments and transit advocates.

“It’s no secret that it’s been difficult for local and state elected officials and community leaders to deal with Secretary Rahn,” said Del. Marc A. Korman (D-Montgomery), a leader in the Maryland House of Delegates on transportation issues. “He’s a smart guy who had decent accomplishments, but he . . . would not be as forthcoming as people would have liked. He would not collaborate as people would have liked.”

Korman praised Slater as “an open, collaborative, responsive administrator,” and added, “I wouldn’t say that I’m glad to see anyone go, but I think the person succeeding [Rahn] will be a good person to pick up the baton.”

Rahn drew praise from transportation advocates who backed the effort by him and Hogan to devote more state resources to highway building.

“The guy came to Maryland to help the governor to achieve game-changing transportation change, and he has accomplished that,” said Emmet Tydings, a longtime member of the Citizens Advisory Committee to the region’s Transportation Planning Board. “He’s taken nothing but a bunch of heat, but he smiles. . . . He’s tried to be pleasant.”

Another transportation sector expert, who supports Rahn but spoke on the condition of anonymity because the issue was politically sensitive, noted: “Greg [Slater] is much more careful with what he says. He’s very diplomatic. The good news is this [change] gives [the transportation department] a chance to have a restart.”

Rahn’s departure came as a surprise to outsiders, partly because he recently took on a high-profile position as a member of the Metro board in July. He did so after a law took effect requiring that the transportation secretary or someone delegated by them represent the state on the board.

But people close to the Hogan administration said there have been rumors for months that Rahn would be leaving because of his family situation. Privately, Hogan lamented Rahn’s decision to step down, according to an individual close to the administration.

“The governor sure . . . didn’t ask him to leave,” the individual said.

Rahn’s departure and Slater’s appointment, which requires Senate confirmation, were first reported by the political blog Maryland Matters.

In announcing the changes, Hogan cited Slater’s service of more than 20 years with the Maryland Department of Transportation. Hogan also said Slater would continue to push the “once-in-a-generation” plan to widen the Capital Beltway, I-270 and the American Legion Bridge, without neglecting transit.

“With his decades of experience, Greg is sure to build on our balanced approach to infrastructure, including record investment in transit,” Hogan said.

Before serving as New Mexico’s transportation secretary for a Republican governor from 1995 to 2002, Rahn worked as an insurance company executive and a county treasurer. From 2004 to 2010, he served as Missouri transportation director, working for a bipartisan state commission.

In both states, Rahn was known for finding new ways to leverage limited government funding. He pursued the same approach with the Beltway, I-270 and American Legion Bridge projects, which he has said will not require taxpayer subsidies because of private investment to be repaid with toll revenue.

But the state’s plan to add the toll lanes recently hit a public snag. Last week, the project came under criticism from state Comptroller Peter Franchot (D), whom Hogan has counted on for the critical second vote needed on the state’s three-member Board of Public Works to approve the project before it can go out for bid.

Asked whether the fact that the toll lane proposal is still facing Board of Public Works approval made the timing of his departure difficult, Rahn said: “It does. I’d wanted to see it all the way through. My decision to leave is not based on the [toll lane proposal]. There’s never a good time to leave. There is always big stuff on the table. While I’d like to see it completed, it just didn’t work out.”

Rahn also brushed off the other controversies that have surrounded him, saying, “We’ve been doing big things, and when you do big things, it generates heat.”

While he was pleased that under his stewardship the state has increased investment in roads, he said, “I believe we still have a disproportionate share of the trust fund going to transit.”

Rahn said that when he first took the job, he was hoping to get back to New Mexico every month or so.

“It’s turned out to be once every three months,” he said. The job “just doesn’t allow the kind of commuting that I envisioned . . . Fortunately, my wife put up with it for 5 years.”

He said he doesn’t know what work, if any, he’ll do next.

“I can’t imagine myself not working, but what that is, I don’t know,” Rahn said.

Michael Laris contributed to this report.