If you've been zipping willy-nilly across parts of the city that have been signal-free for years, don't be surprised at a red light suddenly popping up to stop you in your tracks. That's a portable signal, the traffic police's ingenious idea to help them cope with the nightmare that the city's traffic situation has turned into. "These are signals on wheels, and can be rolled into areas where there is no scope or need to install permanent signals, but which require traffic regulation during certain times, dates or events," said a senior official from the Mumbai traffic police. According to traffic police authorities, the department has already procured around a dozen of these.