It is happening in China, in the city of Zhuzhou, a 6,5 km long tramline who will see the public innauguration in 2018. What is so special about it ? They use PAINT instead of Iron Rails. This is used for the guidance system.
It is alot cheaper of course, buuut …. the iron lines have also other usages, in terms of mobility, in terms of security, in terms of service.
For me is creative, is innovative, but the real test will say if is also usefull