There
are 2,250 transit bus systems in the U.S. alone. Transit buses are
relied upon to provide mobility to all classes of society, reduce
congestion and fuel consumption, and improve air quality. Because
buses are such an integral part of today's transportation system,
pavement quality and durability are vital aspects for their optimal
operation. Portland cement concrete pavements have unique properties
that contribute to a long service life virtually uninterrupted by
repairs or maintenance. They offer superior load-carrying capacity
to withstand the heaviest vehicles and machinery, with reserve strength
for unforeseen overloads. They resist rutting, shoving, and indentations.
Concrete pavements resist subgrade failure by spreading wheel loads,
which is especially important in areas with poor soils. The permanent
surface texture provides traction and safety, regardless of the
elements. Concrete pavements resist chemicals, oil, and weather,
while offering the additional advantages of a clean, attractive
appearance and superior light-reflectance.
Pavements used by buses need to be stronger than pavements used
exclusively by automobiles, since bus axles typically apply heavier
loads onto pavement than the heaviest loaded semi-trailer axles.
In fact, several commonly manufactured articulated transit buses
have axle weights, without passengers, that exceed weight limits
set for the U.S. Interstate Highway System. The pavement alternative,
flexible pavement, has a tendency to move or flow, and eventually
rut, under the stationary load of even an empty bus. And, as transit
systems convert to new fuel-technology buses, pavement distress
may increase, because these new buses are actually heavier than
standard diesel buses.
Urban
bus systems are supported by ancillary facilities such as park-and-ride
lots, pulse points, shelters, and maintenance facilities. Park-and-ride
facilities are constructed to marshal autos destined for central
business districts or employment centers. They are generally located
along major highways or arterial streets outlying an urban area.
Portland cement is essential in providing for all-weather parking
spaces and shelters. Applications might include soil-cement, concrete
pavements and curbing, platforms, and shelters, as well as the approach
roadways and structures. Thus, these facilities accommodate the
automobiles and their occupants who normally would continue driving
to their ultimate destination under congested levels of highway
service. Pulse points are similarly constructed within specific
urban areas to integrate bus routing and intermodal transfer.
Bus maintenance facilities require large expanses of space to not
only queue buses for their daily routes, but also to store, repair
and clean the vehicles. Concrete tilt slab construction is a noted
economical construction process, as is cast-in-place concrete for
the maintenance pits and floor slabs.