|
Slab Track Gaining Momentum
Transit Home >
Slab Track
 |
Rheda Slab Track System in Germany
|
More than ever before, slab track installations and experimental
tests are taking place throughout Europe and Asia. The incentive
is to develop a track structure that will permit high-speed passenger
(speeds greater than 110 mph) and heavy-load freight service to
operate consistently and smoothly with low maintenance costs. The
centuries-old traditional track structure of wood ties and ballast
and its successor system of concrete ties are now being challenged
by innovative concrete slab track structures laid on grade. These
descended from successful slab track installations in tunnels and
on structures where little or no maintenance is the desired goal.
Indeed, ballastless track is on the horizon.
The innovative Bullet Train in Japan clearly demonstrated that
traditional track construction resulted in intensive daily maintenance
and inspection to provide safe operation. As a consequence, the
Japanese RTRI (Railway Technical Research Institute) has experimented
for the past thirty years on various slab track configurations.
They installed test sections and monitored behavior to understand
the distribution of forces on the subgrade, the impact of noise
effects, associated construction costs and maintenance needs, as
well as construction techniques. Currently Japan produces a host
of ballastless designs to apply to variable site conditions. The
designs include grout injection on existing lines, precast slabs
laid to very accurate standards, and, most recently, a ladder track
system that was tested for performance and durability at the Transportation
Technology Center facilities at Pueblo, Colorado. In all of these
installations and experiments, the overriding goal was to reduce
maintenance costs, which in Japan constitute one-third of the operating
budget of the line. All new high-speed lines in Japan are built
on slab track support systems.
 |
Slip-forming operation for ERS slab track.
| A very important effort is being made within Europe to integrate
its railroad systems. Projects include the new generation European
high-speed train programs of the German and French National Railways.
German Railways, when designing permanent way, considers installing
slab track as an alternative to traditional ballasted track. Because
80% to 90% of track maintenance is attributed to conventional track
supported by ballast, they use simulation models including life
cycle forecasting to comparatively predict the behavior of each
system. The new HSL-Zuid high-speed rail connection between Amsterdam
and the Belgian border will likely be built on an all slab track
system situated on piles, due to the high permeability of the in-situ
soils. Elsewhere there are projects under construction using highly
accurate slip-form pavers to produce slab track that meets the tight
tolerances required for high-speed rail. Track fastening systems
have undergone change to adapt to the resiliency needs of slab track.
Highly elastic pads and load pressure distribution plates are used
to simulate the elasticity of the ballast bed. In some cases, the
traditional fastening system is abandoned in favor of utilizing
an embedded rail system. Here, the rail is continuously embedded
in a channel cast within the concrete base slab. None of the traditional
track fastening hardware is needed, as the rail is secured by a
resilient, long-life elastomer. In all of these endeavors, the primary
goal is to reduce the maintenance costs of the roadbed.
Within the U.S., slab track has the potential to be the right application
for the high-speed rail initiative of the Federal Government where
both passenger service and heavy haul freight are characteristic
of shared corridors. Lessons from our global neighbors show that
an up-front premium investment of 30% could yield a payback within
five to twelve years depending on the traffic and gross tonnage
carried. More important is the likelihood that initial cost will
spiral downward as the construction industry adapts to technical
innovations in design and construction equipment. Existing freight
railroads are becoming increasingly burdened by maintenance that
results from the use of heavier cars and fast delivery, which translates
to higher operating speeds and higher costs. In testimony before
the United States Senate Committee on Commerce, Science, and Transportation,
it was stated that an annual budget approaching $8 billion is needed
to maintain the 168,000-mile Class 1 railroad system in the U.S.,
excluding measures to increase capacity. Within the U.S. there are
few slab track applications. Some light rail systems in city centers
are founded on concrete slab track. In some cases they need to sustain
loading from heavy trucks and buses. The true benefit of a concrete
slab track system, however, is a promise to endure the heavy axle
loading of freight traffic while offering a smooth ride for high-speed
rail passengers. Notable slab track installations in North America
include segments of the Canadian Pacific Railroad at Rodgers Pass
and a 1.3-mile track section on the commuter/freight line on the
Long Island Railroad at Massapequa, New York.
References 1. Longi, M. S.,
Concrete Slab Track on the Long Island Railroad, American
Concrete Institute, Concrete in Transportation SP-93, 1986, pp.
405–432.
2. Tayabji, S., Construction Technologies Laboratories, Inc., Concrete
Slab Track for Freight and High-Speed Service Applications, A Survey
of Practice, Portland Cement Association, December 2000.
3. Hanna, A. N., Technical and Economic Feasibility Study of
At-Grade Concrete Slab Track for Urban Rail Transit Systems,
U.S. Department of Transportation, Report No. UMTA-MA-06-0100-81-4,
August 1981.
4. Bilow, D. N., and Randich, G.M., Slab Track for the Next
100 Years, Portland Cement Association, December 2000.
5. Bilow, D. N., and Kucera, W. P., Portland Cement Association,
“Slab Track for Shared High-Speed Rail and Freight Corridors,”
submitted to the A.S.C.E. Journal of Transportation Systems
for future publication, July 2001.
6. Manual for Railway Engineering, Chapter 8, Subpart 27,
American Railway Engineering and Maintenance of Way Association,
Landover, Maryland, 1999.
|
 |
|