As electric cars become an increasingly common sight on Colorado’s roads, the state is ready to target a chunk of the transportation sector that has thus far largely escaped electrification — the thousands of buses, trucks and delivery vehicles that belch greenhouse gases into the air daily and exacerbate ground-level ozone. Colorado’s Clean Truck Strategy, a draft version of which was unveiled this week, targets medium and heavy-duty vehicles — from school buses to 18-wheel diesel-fueled tractor-trailer rigs — that the state claims contribute 22% of the transportation sector’s greenhouse gas emissions in the state. “We’re getting ready to start investing before the end of the year in clean fleet incentives and infrastructure,” Colorado Energy Office Executive Director Will Toor said Thursday. Changes to Colorado’s existing big vehicle fleets won’t be immediate, as battery technology and even hydrogen fuel technology still need to advance to a stage where performance improves and costs come down.