Why All The Emphasis On Branches?

For widespread service in a city or metropolis, it is almost mandatory to arrange the mass transit to focus on one or a few central nodes or hubs, locally thought of as "downtown." Transit lines radiate from there, like spokes of a wheel. Southern California famously spread out from Los Angeles in this fashion, in the early 1900s.

Here is a map of Southern California's Pacific Electric system, which started small but grew to include secondary hubs in Long Beach, Pasadena, and San Bernardino. It become the largest "trolley" complex in the world – with nearly 1,200 miles of line, much of it double-track – and with nearly as many scheduled stops. There must be nearly 100 branches in this 1925 map:
Autos increased the spread, of course, and filled in gaps among population centers. But, as noted elsewhere, it turned out that autos demanded so many (branching) freeways and parking lots that the same region switched its focus back to rail.

Today, in nearly every city of the developed world, streets and highways demand top priority at ground level. Such thoroughfares must also serve trucks, the lifeblood of goods distribution. With subways prohibitively expensive, and buses slow and unpopular, affordable mass transit – the only remaining alternative to autos in the city – simply must be overhead.

Monorails were thought to be the answer; they're sleek and relatively inoffensive. But, as proven again in Las Vegas and Seattle, their two-way lines can't radiate in multiple directions from downtown because they can't branch out. A separate article on this site explains that problem with a diagram, and discusses the few exceptions that only a mother could love.

So there is a tremendous unfulfilled need: aerial mass transit that can radiate out and branch out from downtown hubs. That is exactly what the System 21 monobeam is designed to do, and proved it could do so in 1996. And that is why this particular system was strongly recommended in two landmark books and praised in testimonials by the best of the best in technology and urban planning.

*Exception: there will be occasional tunnels through a major hill or under a major river. Even there, the triangular geometry is advantageous.