the area of a vehicle (for example, an ice cream truck) that is selling merchandise and is displaying flashing amber lights in a school zone when children are present on a road in a "thickly settled" or business district for at least on a road outside of a "thickly settled" or business district for at least on a divided highway outside of a "thickly settled" or business district for at least State highways and other arterials are often posted at in urban areas and in rural areas. A select number of undivided roads are posted at . Divided highways are usually posted at in rural areas as well as business districts. Interstate highways and some non-Interstate freeways in suburban and rural areas are posted at , but many non-Interstate highways are posted at , such as the freeway portions of US 3, US 6, Route 2, and Route 128, or , such as Massachusetts Route 3 South of Boston. Urban freeways are often posted at and occasionally lower, but some rural freeways that pass through urban areas maintain their speed limit, such as the Massachusetts Turnpike through the Springfield and Worcester areas. A "thickly settled district" is an area where building structures such as residential and commercial are less than apart for a distance of or more. This can be subjective since a large part of eastern Massachusetts is built up with many different jurisdictions and different speed limits assigned. Michigan The maximum speed limit in Michigan is . Michigan uses a formula based on the number of driveways and streets, or on the 85th percentile of free-flowing traffic, and if none those methods are used a default applies. In rural areas, speed limits are as follows: Freeway speeds for passenger vehicles range from to . Freeway speeds for trucks and military vehicles is . Non-freeway speeds for passenger vehicles and trucks range from to . Freeways in Michigan are usually signed with both minimum and maximum speeds. By default, the freeway speed limit is , with a minimum speed of for all vehicles, despite a truck speed limit of —effectively permitting trucks only a range of legal speeds. The Mackinac Bridge has a speed limit of for passenger vehicles and for trucks, but can be as low as during high winds. The Michigan Department of Transportation and the Michigan State Police may raise the speed limit to after it