Kakaako has long been envisioned by state planners to become a dense piece of Hono­lulu’s urban core with tall buildings. But development in the area would become much denser and taller under a draft plan tied to the city’s rail project.

Buildings up to 700 feet — almost twice the existing 400-foot maximum in many parts of Kakaako — are being proposed in draft transit-oriented development rules.

Buildings up to 550 feet also would be allowed in some areas of the roughly 450-acre Kakaako region bound by Ala Moana Boulevard and South King, Punchbowl and Pii­koi streets.

The Hawaii Community Development Authority, the state agency guiding development in Kakaako, produced and released a summary of the draft rules Friday which could bring historic change to the area. The new rules are designed to concentrate more residents and commercial enterprises near the two planned rail stations in the area.

Combined with improved pedestrian and bike lanes as well as parking, increased density around transit stations should reduce automobile trips and enhance the existing quality of the Kakaako region, the agency said.

"By reinforcing strong land use and complete streets that access rapid transit, HCDA will develop economically vibrant neighborhoods, improve public health, lower vehicle miles traveled, and reduce greenhouse gas emissions, all while increasing sociability," the draft summary said.

Under the draft, a "limited" number of 550-foot towers would be permitted. Up to three 700-foot towers would be allowed if they are "exemplary iconic buildings with exceptional public benefit."

The draft summary also contemplates allowing a "limited" number of hotels in Kakaako intended for travelers and business people wishing to stay outside Waikiki.

Specific sites permitting hotels and taller buildings aren’t identified in the draft summary. However, HCDA included a map showing about two dozen blocks or block clusters in Kakaako that it said offer the best opportunities for redeveloping under transit-oriented development rules.

One site outside Kakaako, the Hawaiian Electric power plant downtown just makai of a rail station, is also indicated as such a redevelopment site. About 150 acres makai of Ala Moana Boulevard known as Kakaako Makai would include some unspecified elements of transit-oriented development.

Full details of the draft rules are scheduled to be released May 23 on HCDA’s website and at a series of open-house meetings.

Bob Loy, director of environmental programs for The Outdoor Circle, expressed shock at how HCDA proposes to overhaul its development rules.

"Wow!" he said in a email.

Loy, in an interview, said he’s concerned about raising tower heights far beyond the tallest existing buildings on Oahu.

Loy urged the public to pay close attention and provide input on HCDA’s effort. "It is something we need to watch very closely," he said.

Robert Harris, director of the Sierra Club of Hawaii, said the summary is heavy on stock phrases and light on detail. But generally he likes several green design concepts in the summary, including networked bicycle lanes and open public areas.

The Sierra Club has yet to form a position on buildings as high as 700 feet and would like to see more detail about specific building plans before commenting.

"In general, we’re open to the concept," Harris said in an email. "We prefer to see development occur within the urban core, rather than continuing to see more concrete suburban sprawl and loss of prime agricultural land."

HCDA said in the draft summary that new guidelines will better address view issues and tall-building aesthetics, in part by applying best practices to produce well-sited slender towers.

"These buildings will create a skyline of views through and between towers, as well as green spaces on podiums that will enhance views down from neighboring buildings and residential areas on the slopes of Punchbowl, Makiki and Pacific Heights," the summary said.

The summary continued: "The sensitive application of height allowance paired with quality streetscape design can produce the characteristics of a comfortable pedestrian-oriented comfortable environment on the ground plane, while adding to the overall capacity in Hono­lulu’s primary urban center."

To implement the transit-oriented development rules for Kakaako, HCDA will need to produce an environmental impact statement, hold public hearings and have final rules adopted by its board of directors.