Most places worry about speed limits on blacktop and gravel. On Lake Minnetonka, the debate is over how fast people should drive on ice.

The emergence of an icy, temporary transportation system on Minnesota's lakes is a standard feature of winter here. As soon as the ice gets thick enough, that straight shot across the lake or out to the ice house holds real allure.

For years, vehicles of all kinds have been able to go 50 miles per hour by day and 30 mph at night on most of Minnetonka. But closer to shore, they could go only 15 mph, and only to get to the main part of the lake.

Starting this year, as soon as the lake freezes at least 12 inches thick and ice roads are created, drivers on Lake Minnetonka will be able to hit the gas a little harder in places where the rules have been slowing them down: motorists and snowmobilers can now drive 25 miles per hour close to shore and near people and ice houses -- 10 mph faster than before. Snowmobilers will be able to go 50 mph at night as well as day.

Even at that, Minnetonka puts the brakes on ice driving more than most parts of the state. There is no speed limit on most lakes for cars and trucks, although drivers can be cited for reckless driving.

The changes on Minnetonka were made to simplify speed limits and to make the rules more consistent with state law, which sets a 50-mph limit for snowmobiles on all lakes except those in areas with local ordinances, said Greg Nybeck, executive director of the Lake Minnetonka Conservation District.

Not everyone is a fan of lake ice as a wintry speedway.

Lt. Steve Hartig of the Hennepin County Sheriff's Water Patrol, while declining to comment on Minnetonka's changes, was blunt about motoring on ice: "I will never tell anybody to go and drive on the ice. We don't recommend it."

Says Nybeck about Minnetonka's speedier limits: "If it doesn't turn out to be real good we can of course reevaluate it at the end of the winter."

The more controversial change allows snowmobiles to drive faster at night. The Conservation District voted 9 to 5 to exempt snowmobiles from the 30-mph night speed limit, allowing them to run 50 mph at all hours.

Too slow or too dangerous?

Board member Dick Woodruff voted against the change and called it troubling.

"The distance traveled by vehicle going 50 miles per hour is 73 feet in 1 second," he said. "At night that to me seems like a very dangerous situation," since riders may have little time to react if they come upon an ice ridge, open water, or even a cross-country skier in the middle of the lake.

Others who voted against increasing snowmobile speeds at night raised concerns about alcohol and late-night noise.

But snowmobile drivers are pleased with the increased limits, said Pat O'Flanagan, manager at Lake Minnetonka Motorsports in Spring Park.

"It's been too slow for a long time," he said. "It's really hard to ride a snowmobile at the speeds they've had out there. Snowmobiles aren't designed to putt around. It takes the fun out of it."

O'Flanagan said snowmobile technology has vastly improved, making sleds safer to drive at higher speeds. Headlights are brighter and far-reaching, he said, and noise levels are much lower.

The public is just learning about the changes, which were published last week in a new winter rules brochure.

Do's and don'ts

Minnetonka may be the only metro lake to increase driving speeds on ice in recent years, but it's not the only one to regulate driving on frozen public waters.

Minneapolis and St. Paul prohibit driving on lake ice. Many metro communities, including Maple Grove and Plymouth, have speed limits, restricted hours or other rules. Even on Minnetonka, vehicles may not drive close to shore except to get further out on the lake.

"Even though there's not a speed limit [for ice driving] on 99 percent of the lakes in Minnesota, if you operate that vehicle in a careless manner you can still be charged under state law for reckless driving," said Greg Salo, a state conservation officer and captain in central Minnesota. Drivers and their vehicles must be properly licensed and registered, he said, and DWI laws are enforced.

Cautionary notes

Hartig's team posts "thin ice" signs, watches for careless driving and responds to accidents on Hennepin County lakes. He said ice poses many hazards for drivers.

It can be several inches thick in one spot and barely frozen over just 100 feet away, he said. Snow cover makes it difficult to see weak spots. Snow also insulates ice, slowing freezing.

Ducks keep water from freezing in some areas until midwinter, he said. Schools of fish can agitate water and cause weak spots. Ice strength also depends on water depth, currents and other factors.

"The biggest problem is the many things that people can't see," said Hartig. Drivers on Minnetonka have hit bridge abutments and seawalls and have splashed into open water.

Salo said people plow roads to fish house colonies, creating a snow berm that may roll a speeding snowmobile at night.

Fishing houses can be a hazard, he said, for "people zipping through an area, goofing around with their buddies and not paying attention." Reflectors on houses can get covered by snow and ice.

Lightweight fish houses are no match for a 600-pound sled at 60 mph. "We've had snowmobiles go right through fishing houses," he said.

Tom Meersman • 612-673-7388