The Shift to Virtual Blocks
Thanks to advancing technology, the use of virtual blocks on high traffic rail lines is gaining more and more attention. In fact, BNSF recently received patent approval for a home-grown virtual block system that they believe has the potential to increase train capacity, raise average train speeds, and help with the detection of broken rails.
However, to grasp the idea of virtual blocks, we have to take a step back and understand how railroads have been managing trains for more than a century – using fixed block systems.
In a traditional fixed block system, a rail line is divided into sections (blocks) with the idea that, normally, only one train is permitted in each block at any one time. The idea here being that keeping trains in separate blocks is a safe way to move trains over the railroad.
While fixed block systems keep trains apart, they don’t take into consideration that train lengths vary, trains travel at different speeds, and trains have differing acceleration and braking ability.
In other words, fixed-block systems pretty much treat all trains the same – when they actually are not.
On the other hand, a virtual block system, sometimes called a moving block system, treats a rail line as one continuous network, rather than a collection of smaller sections. And, it doesn’t treat all trains the same.
Rather, the virtual block system has the technology to gather and analyze the variables of each train – location, length, speed, acceleration, and deceleration, and use that information to wrap a safe zone around each train on the line. But, the virtual block safe zones arena’t all the same – some have more distance between trains, others less.
A virtual block system needs continuous communication between the train and the railroads central computers to continually analyze the train’s variables and adjust the size of the safe zone as those variables change.
The primary benefit of a virtual block system is increased train capacity – trains would be able to run closer together. Initial studies estimate that single-track lines could see an increase in capacity by as much as 25%. Multiple-track routes would see a smaller increase.
With increased train capacity, railroads would be able to avoid adding track and signals on lines that are currently operating at full capacity.
Virtual block systems would be particularly beneficial on lines where traffic moves at different speeds. For example, a high-priority train could come up closely behind a slower freight, then leapfrog ahead of the slower train at multiple-track, crew change points.
Virtual blocks also would eliminate the need for track-side signals.
Railroads planning to implement virtual block systems will have to file an operating plan, including a safety analysis, with the Federal Railroad Administration.