PORTLAND — The business community has complained for years that getting a development project approved in Portland is so cumbersome and unpredictable that it discourages investment in the city.

The City Council hopes to change that reputation. It voted unanimously Monday to approve a 244-page rewrite of the city’s site plan rules.

The new rules are intended to create a clear and predictable process in which all of the players know up front what the city’s expectations are, said Councilor Cheryl Leeman.

“This is a huge change,” she said.

The new process will replace one that is so ambiguous that decisions often appear arbitrary, said Councilor John Anton.

“It’s like a black box,” Anton said of the system the council replaced. “Applicants go in, and they don’t know what rules they will be subject to.”

The city’s planning staff has been working for more than two years to draft the new regulations. The Portland Community Chamber has been lobbying for the changes, and the reforms are largely in accord with the chamber’s recommendations.

The new rules set standards for projects to be submitted to the Planning Board, benchmarks for infrastructure investments and time lines for the site plan review process.

With the new system, developers will have to change the way they do business, and some may be required to spend more money on engineers and architects.

In the past, many developers have come to the city with vague project proposals and used the Planning Board and the city staff to design their projects for free, said Chris O’Neil, a lobbyist for the chamber.

The new process requires developers to do their own work before starting the review process.

The process allows the Planning Board to require developers to make additional public investments, such as sidewalks or traffic lights. O’Neil called those requirements “extractions.”

The new system sets benchmarks for the level of infrastructure investment so city officials won’t be able to make demands such as requiring a developer to pay for new traffic lights, O’Neil said.

“The old days of going to Portland City Hall to get squeezed should be coming to an end,” he said.

Deb Keenan, a resident who opposed plans for a Super Stop & Shop at Morrill’s Corner, said in written testimony to the city that most development projects are approved fairly quickly.

However, a few large and complex projects have required longer review because of the scale of the projects and because the developers sought exemptions to zoning rules.

“Developers can get a streamlined process easily — by following the existing rules and zoning,” she wrote. “Most do.”