An ordinary bus trip can become complicated when snow or ice affects Seattle's hills and neighborhood streets.

That is especially important for riders traveling between Ballard, Greenwood, Northgate and Lake City.

King County Metro publishes a winter travel guide that explains how service can change in severe conditions.

During major winter weather, Metro may activate an Emergency Snow Network designed around routes it can operate more safely.

The network emphasizes main roads that can be plowed and de-iced while avoiding some steep streets.

Metro says it plans to announce activation a day in advance when possible.

Once activated, the emergency network remains in effect for the full service day even if weather improves.

That means a familiar stop may not be served even when the street outside looks clear.

Start your backup plan by finding the nearest stop on a route likely to remain accessible.

Check how long it takes to reach that stop on foot and whether the route involves steep sidewalks.

Save the transit agency's service-alert and winter-guide pages before a storm.

Metro also provides departure information by text using a stop identification number.

People with medical appointments or shift work should identify an alternative transportation option in advance.

Talk with employers or caregivers about realistic delays rather than waiting until a cancellation occurs.

Do not walk along icy roadways simply to reach a different bus stop.

Residents of Shoreline and Edmonds should check the agencies serving each segment of a regional trip.

A trip that involves more than one provider may have more than one service alert.

Keep a charged phone, a warm layer and a way to contact someone if plans change.

A winter transit plan is a continuity plan for work, school and daily responsibilities.

Metro's official winter guide is the place to verify the latest emergency service information.