Bus Deployments: An Overview

Bus deployments are an integral part of bus operations. They deal with the day-to-day organization of buses, and more specifically, the allocation of buses to various bus routes. The impact of bus deployments is most felt by commuters, who ultimately rely on these buses to commute to their destinations.


Every day, Public Transport Operators (PTOs) must deploy buses to their own bus routes. Bus deployments deal with the dispatching of buses and drivers to their designated bus routes, as well as dealing with emergencies which may require reshuffling of deployments. In this article, we cover three main aspects of bus deployments:

  • Depot / service allocation
  • Deployment limitations
  • Terminology + Emergency arrangements

1. Depot / service allocation

The foundation of bus operations is on the depot level. Every vehicle is allocated to a bus depot, and thus the depot is responsible for its maintenance, storage and deployment. A list of bus depots and bus parks can be found here. At the same time, depots are put in charge of various bus routes, and thus depots are responsible for the daily dispatching of buses. Some bus depots are paired up with bus parks such that buses are interchangeable between them.

While the PTO is responsible for bus and driver scheduling, the depot has to allocate buses (and drivers) to these schedules to ensure that the relevant schedules are being carried out for the day. To do this, a depot frequently pairs a bus with a fixed schedule or bus service. This is commonly known as the permanent bus, or ‘perm bus‘. A fixed schedule may include crossover slots, where buses are scheduled to be deployed to more than one service over the course of the day.

Depending on situation, buses can either be allocated to permanent schedules and services, the latter being more common for services which practice jumpbus (where drivers rotate buses rather than having a fixed bus). These are covered in more detail in the bus and driver scheduling article as linked above.

Not all buses are deployed to their permanent services. When buses cannot be deployed due to various reasons (scheduled maintenance, refurbishment, accident damage, etc), the depot will arrange for another bus to take its place. The large number of buses in a depot ensure that there are sufficient buses to ensure smooth operations even when some buses are taken out of revenue service. All depots keep a small fleet of spare buses, which only appear on revenue service when they are swapped with regular service buses. They also keep training buses, which are dedicated to training and orientation of new drives. These buses are often retrofitted with additional safety features and not deployed on revenue service.

Swapping of buses is a common daily occurrence well-integrated with bus operations. Occasionally, these changes in deployments weigh in significance, and catch the attention of bus enthusiasts, whom frequently refer to these as ‘cameos‘. Transferring of buses between bus depots is also done once every few months to balance out the bus fleet over multiple depots.

2. Deployment limitations

With bus depots free to reallocate buses to different services on a daily basis, a few rules do exist with regards to bus deployments. Fleet restrictions do come into play for various routes where there are limitations to what buses a route can accommodate. With rigid, double-deck and articulated buses on the roads, operators need to put fleet restrictions in place to ensure that buses do not get wrongly deployed to services that cannot accommodate them.

Currently, deployment limitations deal mainly with services which cannot accommodate high-capacity double-deck or articulated buses due to road limitations (such as height barriers, tight turns and road clearance height). Wheelchair-accessible buses (WABs) also have to be allocated to designated wheelchair-accessible bus routes to ensure that services meet their required WAB quota. Only Malaysian-registered buses can be deployed on cross-border services. With the phasing-out of non air-conditioned (NAC) buses, limitations on NAC bus services have been lifted.

3. Terminology and Emergency Arrangements

Aside from running on regular service, bus deployments also involve less-observed phenomena as listed below:

  • 3A. Downroutes

Downroutes are the addition of trips midway along a bus route. They can be either scheduled and unscheduled.

Scheduled downroutes are usually implemented for high-demand services which require the addition of buses somewhere along its route to cope with the demand. They are also common in the early morning with bus routes which are relatively long, notably trunk loop routes. Additional trips start midway so commuters boarding nearer to the end of the route do not have to wait for the first bus to arrive from its starting terminus. Some shortworking trips can be classified as scheduled downroutes. SMRT’s Service 190 is a good example of a route that makes heavy use of downroutes due to overwhelming demand.

Unscheduled downroutes can also be added to cope with demand. The term ‘unscheduled’ can either mean that such trips are arranged but not running on a schedule, or it can mean that the trip was performed without any prior arrangement.

  • 3B. Crossover

Crossovers are scheduled trips that are not performed by permanent buses of the service; but rather by buses from another service that are scheduled to run on that particular service at that point of time. Such arrangements are well-defined on timesheets and are frequently used.

Crossover trips have their uses. They can be used to reallocate resources to different services to better suit demand. They are also used accommodate the operating hours of various services where it would be difficult to fit drivers into a single shift. This is most commonly seen in peak hour services (such as FFW services) where all trips are actually crossovers of other trunk services. Mealbreak crossovers are another common arrangement where a bus from another service is used to substitute for driver who is having a meal.

For SBS Transit, crossovers are usually limited to around two bus services. For SMRT, multiple scheduled crossovers are commonplace, with certain duties performing up to four different services.

  • 3C: Pullover

Pullovers are essentially unscheduled crossover trips. These are usually done as an emergency arrangement where a particular service receives an additional bus from another service when it is severely lacking in buses. As an example, when a bus scheduled for a Premium service breaks down before it can start its trip, a bus from a feeder service can be pulled over to perform the Premium service since the lack of buses on the Premium service has consequences for the commuters relying on the service to get to work on time.

Such occurrences have become more commonplace as a result of more stringent checks by LTA to maintain service standards. Operators may arrange pullovers for bus services lacking resources, otherwise they may face financial penalties.

In rare instances, cross-depot cameos may occur as a result, where the pullover bus is not under the depot of which the receiving service is allocated to.

  • 3D: Special Departure

As their name implies, special departures are scheduled or unscheduled trips performed to increase passenger capacity on a particular route, or as an emergency measure against bus breakdowns and other unforseen circumstances. This definition includes pullovers, and can also refer to additional buses sent from the depot to deal with such a situation.

The term ‘Special Departure’ is used commonly across the website but referring to scheduled downroutes instead.

  • 3E: Lost Trips

Lost trips refer to the reduction in overall number of bus trips, causing discrepancies from published route details. This is usually detected by sudden differences in frequency of individual bus routes. Reasons include mid-route breakdowns, pullovers, and sometimes, even for drivers who are simply unable to keep to their timetable and fall severely behind schedule (this is more prevalent in feeder bus services).

  • 3F: Off Service

Off service refer to buses which go off service, or simply withdrawn from revenue service. There are many reasons for this:

  1. Regular Off service
    Drivers who have completed their daily rounds usually go off service, returning them to the bus depot/bus park or their overnight parking locations.
  2. Overtime
    Occurs when journey time severely exceeds the allocated timetable, such as being stuck in severe traffic jam or where a tree has fallen. Can sometimes be caused by drivers who deliberately drive at very slow speeds, or various unforeseen circumstances like commuter incidents which hold up the entire bus.
  3. Accident / Breakdown mid-route
    Unable to continue with revenue service, breakdown buses (or not-severely-damaged accident buses) go off service and return to the bus depot for further maintenance.
  4. Mealbreak
    At some bus termini without a nearby canteen, buses may go off service as drivers get their meals from somewhere else.
  • 3G: Lay Up

Laying up buses is usually done prior to long-term maintenance work or prior to deregistration/retirement. During this period, buses are exempt from road tax and cannot be deployed on revenue service. By LTA regulations, vehicles not re-licensed after three years will be de-registered automatically at the end of the third year.

  • 3H: De-registration

De-registration of buses is the final stage in the lifespan of a bus, where its vehicle registration plate is removed from LTA records. Buses that are de-registered usually head for the scrapyard or are exported to other countries as second-hand buses. By LTA regulations, a de-registered vehicle must be towed or transported if it needs to be transferred from one location to another, even if it is still road-worthy.

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