Vashon’s small fleet of King County Metro buses will be replaced with new hybrid models this month.

The nine Metro buses that serve Vashon are overdue for replacement, according to Jeff Switzer, a spokesman for the county Department of Transportation. Vashon’s current buses hit the road 18 years ago, and the typical life for a bus is 12 to 15 years, Switzer said.

“By maintaining them carefully, we were able to get more years out of them, but they reach a point of costing more to maintain than replace,” he said.

Vashon’s nine new buses — including three that will be stationed off-island as backup — will be 35-foot hybrid-electric buses that allow the engine to completely cut off when there is no need for power.

The new buses also have lower floors for easier boarding, air conditioning and a function that allows the bus carriage to raise when driving on and off the ferry.

The hybrid buses have fewer seats, but more standing room. While the current buses seat 34 passengers with places for six standees, the new buses have 27 seats and can accommodate 14 standees.

King County Metro began replacing its oldest buses with hybrid models 10 years ago and now has the largest fleet of hybrid buses in the nation. The buses purchased for Vashon cost about $600,000 each. They are currently going through test runs and are expected to arrive on Vashon in early March.