Note: This article is based on chapter 1 of my white paper titled 7 Key CBTC Functions Transit Operators Must Understand. Downloaded it here.
Equipping maintenance vehicles with a Vehicle Controller (VC) is not a function but a decision and operationally a critical one. Maintenance vehicles must coexist with CBTC equipped passenger trains and therefore Operators have two choices; equip maintenance vehicles and follow consistent operational rules or operate unequipped maintenance vehicles and apply special rules.
In a CBTC environment, a train is tracked and protected if it's equipped with CBTC equipment, otherwise special operational procedures must be applied to protect unequipped trains. Operators with a fleet of 60 or 70 maintenance vehicles may opt for rule book consistency and equip maintenance vehicles, whereas small Operators may be concerned about the capital costs of equipping maintenance vehicles and opt for special rules and live with unequipped maintenance vehicles.
Consistency across an operating environment is an important aspect for safety and operational efficiency but every railroad property is unique and how they choose to operate their maintenance vehicles is no different.
Unequipped Maintenance Vehicles – Special Rules
An unequipped maintenance vehicle is no different than a non-communicating vehicle (NCV - see my blog post: How Does an Operator Recover a Failed CBTC Train), it cannot report its position and therefore the wayside cannot protect it. For an unequipped maintenance vehicle to enter the mainline, special rules must apply.
The Operator has two options; implement a Train Protection Reservation (TPR - see my blog post: How Does an Operator Recover a Failed CBTC Train) or implement a fallback mode of operation (see my blog post: Who Needs Fallback Mode of Operation).
TPR
A TPR is a simple but intrusive instrument because of the operational impact. A TPR creates a safe corridor for a maintenance vehicle to travel within while denying permission to other trains.
A TPR is not a viable option for operating maintenance vehicles during Service because of the delays it would create for the riding public. During non-Service hours, TPRs may be sufficient for an Operator if:
Service does not run 24 hours a day
Operator has a small track network
Operator has a small maintenance vehicle fleet
Las Vegas monorail is an example of a system that Operates maintenance vehicles with TPRs. It has 7km of track, the system operates less than 24 hours a day, and the small maintenance vehicle fleet does not enter the mainline during revenue Service hours.
The advantages of using TPRs include:
Simple low cost solution.
The disadvantages of using TPRs include:
Intensive procedure.
Large swaths of track locked down due to the TPR.
Lack of operational consistency: CBTC rule for passenger trains and TPR rules for maintenance vehicles.
Fallback Mode of Operation
Fallback is a more complicated and costly alternative but an operationally less intrusive tool to manage maintenance vehicles.
Fallback implements a conventional signalling system superimposed on the CBTC system to track trains along the transit network. This means that passenger trains will operate under CBTC rules and maintenance vehicles will operate under conventional signalling rules.
Fallback allows an Operator with a large fleet to track, route and insert maintenance vehicles on the mainline during Service with minimal impact to operations (see my blog post: Who Needs Fallback Mode of Operation). Fallback is a viable option for larger Operators but the capital and running maintenance costs are high.
The advantages of fallback include:
Track each maintenance vehicle in the system.
Maintenance vehicles can enter the mainline during Service with minimal impact to Operations.
The disadvantages of fallback include:
Complicated design.
High capital cost to implement.
High running maintenance costs.
Reduced reliability.
Lack of operational consistency; CBTC rules for passenger trains and conventional rules for maintenance vehicles.
Unequipped maintenance vehicles are a viable and cost effective solution for small operators with a limited number maintenance vehicles. But larger operators require a more sophisticated solution where 60 to 70 maintenance vehicles can be tracked and protected at the same time. In this scenario, maintenance vehicles equipped with CBTC equipment becomes a necessity.