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Summary 5
to a new and entirely separate system. Concurrent shared-track light rail operations provide
a mechanism to offer a higher frequency of service than commuter rail, while keeping the
capital costs affordable and enhancing urban passenger and freight rail service. Where
shared-track is the preferred option, the business case should consider:
1. The main reason to consider noncompliant equipment is the improved flexibility it offers.
Constraints in curvature radius, grades, clearance envelopes, limits of acceleration and
deceleration make a lighter rail vehicle a superior choice for a regional service that traverses
both urban and suburban environments.
2. A willing freight partner is essential.
3. Temporal separation while adequate, limits both using parties, and can be unaccept-
able for freight customers, and restrict special events services for transit. It is also more
difficult to schedule maintenance-of-way (MOW) windows on a temporally-separated
system.
4. A strong oversight function and negotiation skill is essential.
5. Local governments should deal with the railroads as peers in negotiations and in business
transactions. However, state or local authorities may have the right of first refusal if the
freight operator proposes abandonment.
6. All planned improvements should benefit both the freight and passenger operation.
A business case for improved technology is more easily made where risk to passengers can
be significantly reduced. A freight operation also receives benefits, but the business case for
the use of state-of-the-art technologies on a freight branch line is not particularly strong.
Train Control Technology
Systems to back up the operator have existed for over 100 years. The rapid development of
new processor and communications technologies has vastly increased enforcement options,
and more importantly, safety capabilities. Conventional signal systems rely on train opera-
tors correctly observing and conforming to wayside signals, plus applicable radio messages
and written operating rules, timetables and bulletins for safe train separation. Modern signal
systems, standard to many high-density transit systems, employ different ways in which sig-
nal aspects and other instructions can be transmitted to the train and enforced, even if the
operator fails to observe these instructions. The most important factor in choosing a train
control system is to ensure an adequate level of collision safety.
However a shared-track train control system that permits progress beyond "rigid temporal
separation" and allows a true concurrent train operation should incorporate other desirable
features and capabilities:
· Short block lengths;
· Multiple signal aspects;
· Automatic train stop to override operator error and prevent rail vehicle collisions;
· Prevent/protect track to track crossing conflicts and siding roll outs;
· Accommodate different performance characteristics of passenger and freight equipment;
· Provide for operator alerts and a visual transition zone when going from signaled track to
street running territory;
· Provide hazard warning and avoidance systems; and
· Accommodate equipment that may not be recognized by the train control system on
the line.
A shared-track operation requires no advanced or exotic technology to provide adequate
safety when the preceding guidelines are applied. The benefits and advantages of the latest
