Building one 11-mile segment of commuter rail from Westminster to Broomfield could cost as much as $681 million while about 100 miles of enhanced bus service in the northern suburbs would cost roughly half that and serve nearly eight times as many passengers, according to an analysis for the Regional Transportation District.

HNTB consultants assessed the costs of transit options for Denver-to-Longmont commuters as part of a study of

the mobility needs of the northwest area that began last spring.

RTD agency hopes to bring a recommendation of the best transit option — commuter rail, bus rapid transit or a combination of both — to the governing board for a vote in early 2014.

Part of the final decision will hinge on what the communities along the northwest corridor prefer, said RTD General Manager Phil Washington.

“This is a collaborative effort and we want to reach a consensus with the stakeholders,” Washington said.

RTD and the communities on the corridor agreed in July to evaluate building the Northwest Rail Line in segments. The first segment would extend the line to Broomfield from its current end-of-line location at 71st Avenue and Lowell Boulevard in Westminster.

That stretch would cost from $557 million to $681 million, with daily boardings in 2035 estimated at 2,100 to 3,400.

At least third of the cost is due to a fee RTD would have to pay to the BNSF Railway for the use of its track, officials said.

The Broomfield to Louisville phase could cost up to $194 million; Louisville to Boulder as much as $295 million while Boulder to Longmont could cost $243 million.

Extending the North Rail Line, which runs east of Interstate 25, from Colorado 7 to Longmont could cost $682 million to $834 million, according to RTD estimates.

Meanwhile, a bus rapid transit system that would serve arterial routes in the north area could range in cost from $255 million to $300 million, with daily boardings in 2035 estimated at 16,300 to 26,600.

Monte Whaley: 720-929-0907, mwhaley@denverpost.com or twitter.com/montewhaley