Looking at an artist’s rendering of an attractive tree-lined walkway presented to the West St. Paul City Council last week, Council Member Dave Napier said: “This is what I want for Robert Street.’’

The sketch was presented by SRF engineering consultants after Council Member Jenny Halverson persuaded council members to think some more about the huge Robert Street reconstruction. She saw it as an opportunity to add beauty and character to the city by giving it distinctive landscaping that includes boulevard trees.

But a new urgency has arisen for the project. The cost has gone up again, by $4 million, presenting a new challenge for the city to find more funding.

Because the landscaping also will require millions — and because the City Council is far from agreement on exactly how many trees would be included, where they would be placed and how the city would pay for it — the City Council made a key decision: that the road construction and the landscaping would be split into separate projects.

The road construction will go ahead as scheduled over the next three years so that the city will not risk losing the $7 million it has received in federal funding. The landscaping along on either side of the street will be done — according to an as-yet-unspecified schedule — after the City Council agrees on a plan.

The revised cost estimate came from SRF, which is managing the project for the city. It put the cost of the project now at $26.8 million, up from $22.2 million. That leaves the city with a $4.6 million gap in the money available to pay for the project.

Halverson, who has been the strongest advocate for boulevard trees, said she opposed splitting the landscaping off from the road construction because it is such an important part of the project.

She repeated her view that the Robert Street reconstruction, which is the largest public works project in the city’s history, should be done right, with landscaping to make the kind of improvement in the community’s appearance that residents expect and that the city needs.

Halverson said after the meeting that the majority of the council members “approved a plan to move forward on a project that has an undefined, and seemingly growing, budget, and they have no idea what the project will look like in the end and no decision as to how or when the ‘second phase’ of the project will even be undertaken.”

The cost of the project was last revised from $10 million to $19 million in 2012.

Some part of the new $4.6 million gap in funding will have to be covered by issuing city bonds that West St. Paul taxpayers would pay off over years, City Manager Matt Fulton told the council.

And the city also has asked the Minnesota Department of Transportation to consider whether it can provide more money for the project.

Robert Street is a state road, and the state is already providing nearly 40 percent of the money for the project, said Sheila Kauppi, MnDOT’s south metro engineer. “Only certain elements can qualify for state funding, and we are within a million of that threshold right now. We are going through an exercise to see how much MnDOT would be able to add to the project,” she said.

One option MnDOT is considering is turning over Robert Street to Dakota County or to the city, Kauppi said. The state would save money if it no longer was responsible for maintaining Robert, so MnDOT is trying to quantify how much that would be.

If the city or the county wanted to accept jurisdiction over Robert Street and take on its maintenance, that would be money MnDOT could put toward the $4.6 million funding gap.

The rise in the project’s cost adds new pressure to the boulevard tree discussion because it could add millions more that the city would have to shoulder.

To line Robert Street with trees in the fashion depicted in the artist’s sketch, the city would have to purchase a 3.5-foot strip of land on either side of the street for the full 2.5 miles of the project.

That strip would be used for a sidewalk running along a strip of land closer to the street that would be ornamented with paving stones and reserved for trees, streetlights, benches and signs.

The city has not yet released estimates of how much it might cost to buy land for the landscaping from the many private landowners that line Robert.