Lausanne is arguably the smallest city with a metro in the world (rubber-tired M2). Line M1 however is entirely single-track, with passing points at most stations. The trains run every 7-8 minutes,and every 5 minutes at rush hour. It was originally branded as a tram line but was rebranded as a metro line to match the other rubber-tired metro line built in the city, M2. I love this weird "metro" line.