Signs posted on Interstate 394 west of Hwy. 100 tell motorists: "Do Not Cross Double White Line."

The medium-size white signs with black letters seem to carry a simple and clear directive.

But because the double white lines separate the general traffic lanes from the MnPass lane, some motorists wondered if the "do not cross" signs apply only to the hours in which the high-occupancy toll lanes on I-394 and I-35W are in effect.

In short: No.

Double white lines are not to be crossed at any time, according to the Minnesota Manual for Uniform Traffic Control Devices, the state statutes that spell out traffic controls on public streets, roads and highways.

"Although the intent [with the double white lines] is to limit lane changes during peak hours when the lane is restricted to MnPass use, the double white lines are restricted at all times of day," said Brian Kary, freeway operations engineer for the Minnesota Department of Transportation.

High-occupancy lanes on I-394 and on I-35W from Minneapolis to Burnsville are generally in effect from 6 to 10 a.m. and 3 to 7 p.m. weekdays. At all other times, including weekends, the lanes are open to all motorists unless otherwise noted.

Motorists who opt to use the toll lanes in off-peak hours must stay in their lane until they reach a point where the solid lines break.

Adding to the confusion on I-35W is that the double white lines appear only sporadically, such as in the Crosstown Commons, near I-494 and in the vicinity of the Minnesota River bridge.

"[The rule] has to be in effect all the time, otherwise people are stuck trying to figure out if it's between 4 and 8 and they can't cross over into that lane," said Lt. Eric Roeske of the Minnesota State Patrol.

The rule also applies when a single white line splits in two, such as at an exit ramp where one line defines the outer edge of the highway lane and the other veers off to define the exit ramp; in those cases, it is illegal to cross the two sets of lines.

One area where this happens frequently is on westbound I-94 at Mounds Boulevard. When traffic is stacked up on the three through lanes into downtown St. Paul, many drivers use the two right lanes to zip up to where Mounds splits off from 94, then cut across two sets of lines marking the area between the freeway and Mounds. Then they get back onto 94, thereby bypassing the traffic jam.

"I've written lots of tickets for that," Roeske said.

In contrast, it is legal, but not advised, to switch lanes that are separated by a single solid line, such as those in the Lowry Hill tunnel on I-94 in downtown Minneapolis and those in the bridge construction zone on westbound 494 near Xerxes Avenue in Bloomington. A wide solid line is an advisory marking.

"It is similar to a yellow sign in a curve that says 45 miles per hour," Roeske said. "That doesn't mean the speed limit is 45. It means that would be the appropriate speed for that area. So it is better to stay in your lane, but it is not illegal to switch out."

Violators who cross double white lines can be cited for failure to obey a lane marking, which carries a fine and court charges of up to $128, according to a courts fee schedule at www.mncourts.gov.

Follow news about traffic and commuting at The Drive on startribune.com. Got traffic or transportation questions, or story ideas? E-mail drive@startribune.com, tweet @stribdrive or call Tim Harlow at 612-673-7768.