“Since the ART is a guided bus system, ruts and depressions will be worn into the road by the accurate alignment of the large number of wheels. Reinforcement of the roadway to prevent problems and avoid future maintenance may be as disruptive as the installation of rails of a light rail system.” - wiki Autonomous Rapid Transit
Just lay the rails and run some wires and have a tram.
A trackless tram is a shitty bus which can't run on suburban routes or navigate corners well, it'll require its own infrastructure (depots) and because it isn't a tram or a bus it'll live on as its own slice of PT on its own for a few decades and require replacement anyway, either as busses or eventually upgrade to a tram.
Tommi_Af: And not as energy efficient as rail transport either! Rubber wheels produce a lot more rolling resistance than metal on rails, thus requiring more 'oomph' to keep going at a constant speed. AND they'll deteriorate faster than metal too, requiring more frequent replacement. Of course, rubber does have some advantages such as the ability to climb steeper grades, but if they need that, they should just build a fast and reliable bus service with dedicated lanes/right of way etc. All the work I've read and done on transport planning has pointed to people preferring convenient (i.e. fast, reliable, affordable, safe...) modes over anything else so without that the trackless tram bus thingies will be a complete waste of money.