Using one of the southbound lanes on Cedar Avenue for northbound morning traffic, creating the metro area’s first reverse-flow “zipper lane,’’ would cost about $56 million, according to new estimates by the Minnesota Department of Transportation.

It would be the most expensive of three options the department is considering for adding a MnPass lane on northbound Cedar Avenue.

MnPass lanes are express lanes for buses, carpools, motorcycles and solo drivers who pay a toll. Tolls are collected electronically, and solo drivers pay a higher price as congestion builds in the general lanes.

MnDOT considers the lanes an effective way to deal with congestion. In consultation with Apple Valley, Bloomington and Eagan, the department is exploring three ways to add a MnPass lane to northbound Cedar because it is so jammed during the morning, it takes almost 27 minutes to drive the 10 miles from 138th Street in Apple Valley to Crosstown Hwy. 62 in Minneapolis.

Cedar is the first freeway in the Twin Cities metro area where a zipper lane has been considered. It’s an option for Cedar because the traffic split is so pronounced.

In the morning, 80 percent of the traffic on the freeway is heading north and 20 percent is heading south. That would make it possible to borrow a southbound lane and use movable barricades to open and close it during the morning rush hour, in an operation that resembles the movement of a zipper.

But in cost and time comparisons just presented by MnDOT, it shows up as the most costly and least effective option.

A zipper lane would cost about $56 million and deliver a northbound morning trip time of about 10 minutes. With the zipper lane added to the freeway, the travel time for traffic in the general lanes would be 22 to 24 minutes, compared with about 27 minutes now.

A second option — widening the freeway and using the shoulder to create the MnPass lane — would cost about $46 million and give users of the lane a seven-minute trip up Cedar in the morning. With the freeway widened to add a MnPass lane, traffic in the general lanes could make the trip in 14 to 16 minutes.

A third option — half widening and half zipper lane — would cost about $47 million and give morning bus riders, carpoolers and toll payers a 7.5-minute trip. With this combination lane added to the freeway, traffic in the general lanes could make the trip in 15 to 17 minutes.

These options will be presented and explained to the public from 4:30 to 6:30 p.m. Oct. 2 at Eagan City Hall, 3830 Pilot Knob Road.

An advisory group with representatives from MnDOT, Dakota County, Apple Valley, Bloomington, Eagan and the Metropolitan Council is scheduled to forward their choice among the three options to MnDOT and Dakota County by the end of the year.

How soon the recommendation might be acted upon is unclear. The project is not in MnDOT’s budget and there is no timetable for adding a MnPass lane to Cedar, said Jon Solberg, south-area Dakota County planner for MnDOT.

Deciding on the best MnPass option is complicated by the fact that the MnPass lane must work well with transit buses on Cedar Avenue, Solberg said. The Cedar Avenue Red Line bus rapid transit line opened on Cedar in June. A key question is how the BRT buses would use the MnPass lanes.

MnDOT has made it a goal for the MnPass option to complement freeway changes that would be necessary to provide a faster stop for Red Line buses at the Cedar Grove station in Eagan. Several options for providing a faster stop are being studied, along with the three MnPass options.

One of the main reasons for building a MnPass lane is to give transit an advantage on the freeway. If for some reason buses can’t get to it or don’t want to use it, the MnPass lane becomes far less attractive, Solberg said.

A key decision about the cheapest MnPass option — widening the freeway and using the shoulder to create a MnPass lane — is whether the Red Line must have the shoulder.

Currently BRT buses use the right shoulder through Apple Valley and may use the shoulder on Cedar if they encounter traffic congestion in the general lanes. Whether preserving the shoulder for buses will be necessary if a MnPass lane is built is one of the questions that must be addressed in finding the best MnPass option, Solberg said.