On-time performance

Transport hubs

Users of transport systems often use several transport modes to complete a journey. They will change transport modes at a transport hub, and all transport modes have some kind of transport hub.

On time performance is important to interchanges. Where on time performance is poor, passengers or goods may miss a connection, and so be forced to wait. In some cases, the transit time allowed from one transport mode to another may be very small, and so any lateness can result in services being missed. Where services are infrequent, such as a long-distance train trip, or a flight, then the consequences of late services can be high. Transport systems that exist to deliver passengers and services to interchanges should be particularly concerned with achieving a good on time performance.

Measurement

Typically on time performance is measured by comparing each service with its schedule. A threshold is chosen for how late a service can be before it is determined to be late.

The scale of delays are often calculated in delay minutes. A delay minute is the number of minutes a service is delayed multiplied by the number of passengers on board the transport vehicle.

Network Rail, a large rail infrastructure provider in the UK, uses passenger delay minutes as a mechanism to reward and punish for services being on time and late respectively. Using delay minutes as a measure allows for comparisons between heavily loaded large transport vehicles, and much smaller or lightly loaded vehicles. The economic cost of a large transport vehicle being delayed is much greater than a service that is almost empty.

Factors

There are many factors that can affect on-time performance. Depending on the situation, the service may face regular delays or a service that usually performs on time may be occasionally behind schedule. Some of these factors include:

• Traffic congestion:
  • Bus transport: The volume of automobile traffic on the bus's route can affect the bus's ability to keep on the schedule. While a route that is free of obstruction can remain on schedule or even move ahead of schedule, heavy traffic can slow down the bus behind its schedule. This can be due to regular conditions at the time of day, or an occasional or one-time event, such as a sports game or festival that draws a large crowd.
  • Rail transport: The volume of traffic on the route can cause even more delays for rail vehicles, because of tight scheduling at sidings and other meet points. On passenger railroads, freight traffic is especially problematic because of the length and slow acceleration of the freight trains.
  • Ferries are often affected by congestion at quays and piers. One report reported a third of all delays are caused by congestion.
• Accident: A collision that obstructs traffic flow can also tie up vehicles on the route until the accident is cleared and therefore cause them to be behind schedule.
• Breakdown: A disabled bus or train, besides being unable to complete its own route, may slow down others that follow on the schedule. As riders scramble to board a subsequent bus or train on the schedule, the higher ridership levels on that run may slow it down. Additionally, on a rail line, a disabled train may block other trains from passing, or may require track-sharing with opposing trains, thereby slowing service in both directions.
• Detour: A road closure that forces the bus to temporarily deviate from its regular route may cause it take more time than planned to reach its destination.
• Passenger load: When a special event takes place, the service may experience higher ridership levels than usual, leading to more time the bus or train may have to spend allowing passengers to board and depart.
• Unrealistic scheduling: Many public transportation agencies are tax-subsidized, and therefore are often cash-strapped while attempting to maximize service provided to customers. In such cases, schedules that are written do not provide enough time for operators to travel along the route in the time allotted, and layovers are too short to allow enough recovery time, thereby seriously delaying the service on a regular basis.
• Weather: Inclement weather may cause a bus that usually remains on schedule to be behind as a result of precautions that must be taken by the vehicle's operator and other vehicles on the road. Trains might have to operate slower as a result of slippery rail during the autumn season, and high wind can affect signal systems.
• Crewing issues. Crew may be late to work, or be at the wrong place at the wrong time. Alternatively, they may make mistakes that delay services.

Effects of poor on-time performance

The effect of delays to a transport system are normally calculated as costs in dollars, either to the passengers, or to the transport provider. The transport provider will incur costs of the additional use of the vehicle, crew costs, and fuel. In many cases the cost is calculated as a dollar value per minute. The total cost of delays for an entire transport system for one year can be very large.

In many publications the effect of poor on time performance is equated to lost money. As passengers are delayed, this delay is equated to dollars, and this is the amount that is lost. Calculations are performed for the total amount "lost" per year for different countries, for example, for the US it was estimated that the cost to the country was $32.9 billion in 2007. The total amount of cost per country per year can be very large.

An economic cost is calculated through the following formula:

The delay cost per minute is calculated as the addition of direct costs to a service provider, and the economic cost to passengers through lost time. This is:

The economic cost per minute for passengers is often expressed as a percentage of the average in the area. For different transport modes the cost per minute may be different, as those using buses may have a lower income than those using trains.

Buses when late may experience a problem known as bus bunching. On some bus lines with a more frequent service, if one bus falls behind schedule passenger numbers waiting at bus stops may grow, required a longer layover time. One or more subsequent buses on the published schedule may pass these already cleared stops and have a nearly empty run, and may actually jump ahead of their scheduled time to the point that two or more buses are within close sight of one another. In some cases, one bus is able to pass another. This phenomenon is sometimes known as clumping or bunching. When this occurs, the even spacing of buses on the schedule may be severely disrupted, leading to extremely long waits for those attempting to catch a bus, and multiple buses arriving at once. Bus bunching serves to reduce the effectiveness of buses as a transport mode.

Improving schedule adherence

Transit agencies often take the following measures in attempts to improve schedule adherence on their routes:

• Providing better information to drivers on their schedule and on time performance. Bus and rail drivers may not know if they are on time as this information is not commonly provided. A driver advisory system (DAS) can provide better information, and can inform drivers of their correct departure and arrival time.
• Adding additional route capacity, so the effect of bottlenecks is reduced. Capacity constraints are common in many transport systems, and adding capacity is normally an effective way to reduce delays.
• Modify schedules by adding running time, known as schedule padding. This is the most common solution, but agencies often add running time by cutting layover time, which adversely affects the ability to recover from unplanned incidents. If layover time is to remain the same, it may require an increased expenditure in the system's budget or a slight reduction in the number of trips.
• Increasing the number of reserve vehicles. All transport vehicles can experience engineering failures, which cause them to be unavailable for service. Increasing the number of reserve vehicles increases costs, but allows vehicles to be replaced when needed. For this strategy to work vehicles need to be placed at strategic locations.
• Modifying routes to a route where buses can be less obstructed, when this does not interfere with the ability of riders to reach their buses.
• Building bus and rail lines which are grade separated from road traffic.
• For airlines, delays are often caused by ground processing at airports, so improving the airport plane and passenger handling can have a big effect of on time performance.
• Splitting a long route into two or more shorter ones, as shorter routes are more likely to remain on schedule. Shorter routes generally are exposed to fewer problems.
• Some cities have introduced bus rapid transit services or limited stop lines on long, overcrowded routes. This involves the use of part of the route's budget to operate another line on the same route that stops only at key points. While the overall frequency of the original route is reduced, riders traveling over a longer distance have the option of obtaining a quicker trip on the limited-stop line.
• Some agencies and transport companies have installed GPS devices on their buses and trains to monitor the locations of the vehicles. By linking this real-time information with stop locations and predicted travel-times, the estimated time of arrival of the next service is then displayed at some stops.
• Customer interfaces: Some agencies and companies have made the GPS tracking data described above available to public transport users online, by a toll free number, or through the mobile web.

Real-world examples

The following chart shows some examples of real-world on-time performance. The figures are always (unless stated otherwise) per vehicle, not per customer.