Traffic Lab is a Seattle Times project that digs into the region’s transportation issues to explore the policies and politics that determine how we get around and how billions of dollars in public money are spent.

Drivers who carpool in the Highway 167 express-toll lanes will need a state GoodtoGo! FlexPass starting Monday to keep their free trips, instead of being dinged for the posted toll rate plus a $2 surcharge.

At the same time, the corridor will be divided into three zones, so that tolls paid by solo drivers will vary by destination, instead of a single rate for the whole distance between Auburn, Kent and Renton. New lane stripes and signs mark the legal merge locations for each zone. Some drivers taking short trips will pay less than before.

Both adjustments are designed to matc

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