The quest for improved transportation systems continues as control
technologies become more sophisticated and alternative propulsion
systems are tested. 
While
electric motor propulsion is taken for granted in most operating
systems, other propulsion means such as cable, air, air suspension,
and magnetics are possible. Several systems generally classified
as Personal Rapid Transit (PRT) or Automated People Movers (APMs)
have been developed and are in service, under test, or are conceptualized
to meet specific transportation needs. Whatever the form of propulsion,
technologies in transit seek to minimize the cost of the fixed guideway.
It has been reported that more than half the total cost of a system
is relegated to construction of the guideway and its supporting
system. Concrete for innovative as well as conventional transit
system guideways has therefore emerged as the material of choice
because of lower cost as well as versatility and availability of
material. Manufactured or cast-in-place concrete slabs, box beams,
double tees, bulbs, and I-sections are integral components of transit
service. These products are the result of technological advances
in concrete design, mixes, and manufacture to yield higher strength
and long life structures.
Personal Rapid Transit Systems (PRT's) are distinctive by definition.
They feature small vehicles on fixed guideways and are demand responsive
with all trips categorized as non-stop. These systems incorporate
small vehicles with capacity no greater than 6 passengers. Mostly,
these systems have been developed as supplementary feeder connections
to existing transit. The Morgantown system connecting West Virginia
University with the Morgantown Central Business District is probably
the best example of a PRT system operating today. One exception
however is that it's car size (21 passengers) does not fit the true
PRT definition. Automated People Mover Systems, on the other hand,
feature vehicles of greater capacities running on fixed guideways
as a line haul system with fixed schedule service. Many APM type
systems can be found in airport people movers in principal U.S.
cities.