Santa Barbara’s city bus system celebrates 50 years as the Metropolitan Transit District on Wednesday, but its antecedents date back to 1870. A pop-up MTD Museum on March 27 at MTD headquarters will look back and forward 50 years, from its start with 12 buses on six routes to 112 today serving 42 routes. Along with MTD’s 2030 goal for a 100 percent zero emission fleet, a special program at 11:30 a.m. will discuss the future of “microtransit” — or a curb-to-curb, on-demand system — smartcards for payment, service apps, and new facility upgrades. The museum will be up from 11 a.m. to 1 p.m., and the program starts at 11:30 a.m. It all happens at MTD headquarters, 550 Olive Street.