Besides turning powered wheels embedded in a thin non-bending wall, the inability to exit a freeway without a stop light, the need to raise every bridge on the route, the risk of drivers drifting into the wall for a myriad of reasons (one minute a white dotted line, next minute a tunnel), the elevated station construction, and the added cost of requiring buses built on stilts it seems like a pretty practical replacement to a bus. Although a daddy-long-legs bus would be better.
Silly TTC engineers not rushing to roll this out. What is wrong with them? First they turn down swan boats and now this.