MI SB0898

Replaces discretionary speed limit authority based on engineering/traffic investigations with a mandatory formula requiring speed limits be set at the 85th percentile of free-flowing traffic speed, rounded to the nearest 5 mph increment.

Requires minimum speed limits equal to at least the 75th percentile of free-flowing traffic speed under ideal conditions, with automatic rounding up to the next 5 mph if rounding down would fall below this threshold.

Allows road authorities to post advisory speed signs where highway design features have lower design speeds than the 85th percentile traffic speed.

Requires all modified speed limits to be documented as traffic control orders filed with county clerks (for state/county highways) or local officials (for local roads), with certified copies serving as legal evidence of authorization.

Changes speed limit violations from absolute speed limits to civil infractions and establishes definitions for county road commissions, design speed, local road authorities, and traffic control orders.