By Noel T. Braymer
Metrolink was first to get a fully operational Positive Train Control (PTC) system on line for all their routes in this Country. Recently I traveled on Metrolink and on 2 trips my train left a few minutes late. The reason for the late departure given by the train crew was Positive Train Control. The problem is the slow download time when starting a new route which has to be loaded in the PTC on board computer. I don’t have all the facts to explain why this is so. But it seems odd given how cheap computer memory has become that the on board PTC computer has to have a file reloaded when changing routes. This has been an issue for a while. This brings up a question when run through tracks are finally built at Los Angeles Union Station: will run through service have 2 routes ready for the PTC computers on the trains? A major reason for run through service is to expand the number of direct markets for passengers and reduce running times for passengers on long trips. How long does it take to download these routes to the on-board PTC computers and why is it taking so long?
So far I can’t find all the answers to my questions. I did find out that the on board PTC computer in the locomotive has to be regularly updated for each route during the day. This is because the conditions on a route can change during the day. Routes can have changes with slow orders, track work and other changes during the day. All of these issues have to be monitored by the onboard PTC computer. A common issue would be slow orders on a route. For example if the train’s operator forgets about a segment with a new slow order. The on board computer should have it in its memory first to alert the operator of the on coming slow order. If the operator fails to react then the computer would slow the train to the proper speed.
What I have been doing is reading up to find out how PTC works. Out of the roughly 140,000 miles of railroads in this Country, “only” 60,000 miles of this will be required to have PTC. Even this 60,000 miles of PTC was estimated by the Federal Rail Administration to cost around $14 billion dollars to install. But these 60,000 miles represent the busiest rail lines in this country carrying the bulk of freight and passenger trains. Most of the trackage which will not require PTC are so call “dark roads” which are single track branch lines that often don’t have signals and rarely have 2 trains on the line at a time. There are 2 ways to install Positive Train Control. One way is build everything new with what is called CBTC which stands for Communication-Based Train Control. This is the type of system which would be required for a High Speed Rail Passenger service. This system can be used to fully automate operation of trains. Data for this system is transmitted in digital form. It is also the most expensive form of Positive Train Control.
What most of the railroads are doing for PTC is using an overlay-type system, which means they are adding sensors, signals and transponders to their existing signalling, switches, crossing gates and so on. These will be connected using wireless transmission of these data communicating with computers both in the locomotives as well as at dispatching centers. The on-board locomotive PTC computer constantly calculates the amount of time and distance to bring the train to a full stop in case there is a need for an emergency stop. There are several such systems being used by the different railroads. A common one is called Electronic Train Management System (ETMS). This transmits wireless data from locomotives, switches, signals and so on which are picked by Base Stations which relays this data by cable to Network Operating Centers. A major difference between ETMS and CBTC is ETMS is an analog system while CBTC is digital. So what’s the difference? If you are old enough to remember vinyl records played on record players, that’s an example of analog data. Before the music played you could hear background noise between tracks. CBTC is digital, which is much faster and more reliable. Most music recorded today are on digital files which have almost no if any background noise.
The main theme for PTC is what is called Interoperability. The reality is that there are several different PTC systems on the market, and there are different systems being bought by the different rail operators. The problem is all of these systems have to work together, even though they are different. Railroads often share and use other railroad lines. A classic example of this would be the Pacific Surfliner. Between San Diego and Camp Pendleton, the North County Transit District of San Diego County controls the railroad. For most of Orange County Metrolink I believe dispatches and maintains the rail line. From Fullerton to Los Angeles the train is on the BNSF. Between Los Angeles to just short the city of Ventura Metrolink again controls the railroad. Past Ventura up to San Jose the railroad is owned and controlled by the UP. Between San Diego and San Luis Obispo there are maybe up to 4 different Positive Train Control systems in place that have to be compatible with each other.
So have I discovered why it takes so long to download data for PTC on current rail service such as on Metrolink? While I can’t say for sure, my guess is much of the data is transmitted with analog by most of these PTC systems which is slower to transmit than digitally. Today with a home computer whole albums of music and be copied in seconds as computer files. Transmitting data digitally is usually faster than any analog system. We are now so use to going online for information, music or other forms of entertainment and it is downloaded usually in seconds. If what I assume is true, it will be some time before PTC will be fully digital. That could mean slow transmission of data from the central computers to the on board computers to the trains. I wonder if there is someway to transmit this data like a smart phone digitally and wirelessly to the locomotive PTC computers? But the big question to that is who will pay for it?
For more information about Positive Train Control, click to this web post Positive Train Control (PTC): Overview and Policy Issues