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Glossary

Browse the A-Z below for some rail-specific terms that are used in this website, together with their meanings.
 

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P

PACTS

Parliamentary Advisory Council for Transport Safety

PCAW

Public Concern at Work

PDAC

Performance Data Accuracy Code : Establishes the standard of recording of the times at which trains arrive at, depart from or pass specified points, and the difference between those times and the corresponding times published in the Working Timetable.

PDI

'Possession disruption index – passenger' (PDI-P) and 'Possession disruption index – freight (PDI-F)': a graph indicating the level of disruption caused by possessions over a period of time.

Network Rail needs to restrict access to the network to carry out many of its maintenance and renewals activities.

These restrictions of access are referred to as possessions. Possessions are considered to be 'disruptive' if they impact on the running of passenger or freight operators' normal timetabled services.

Percentage point

The unit for the arithmetic difference of two percentages.

Performance order

Directs a party in breach of contract to do, or refrain from doing, anything that the arbitral tribunal making the order considers just and reasonable in the circumstances.

Performance planning process

Network Rail decides what resources (operational, maintenance, renewals) it needs to put in place in order to deliver the required performance target set by the Government.

Periodic review

See PR08 and PR13 definitions.

Permitted business

Permitted business means the Network Business and the Permitted Non-Network Business of Network Rail.

PIM

The Train Accident Precursor Indicator Model (the PIM) managed by the Rail Safety and Standards Board (RSSB), measures the risk, per million train miles, of a train accident - i.e. collision, derailment, fire or striking a road vehicle on a level crossing. The measure incorporates 82 precursor events in eight groups. Around 65% of the risk arises from events largely under the control or the responsibility of Network Rail, e.g. track geometry, infrastructure failures, environmental factors (flooding, land slips etc.) and level crossing misuse.

The PIM risk indicator was set to a reference value of 100 at the end of March 2002 and the PIM risk indicator provides a measure of the change in risk relative to this level. A reduction in the index is therefore beneficial, denoting a reduction in risk.

Points failure

A fault within a set of points (switches and crossings).

Possessions

Network Rail needs to restrict access to its network to carry out many of its maintenance and renewals activities. These restrictions of access are referred to as possessions.

Possessions returns

The time by which Network Rail has completed its maintenance and renewals activities and train operators can resume their use of the network to operate their services. 

PPM

The Public Performance Measure (PPM) is the percentage of franchised passenger trains which arrive at their destination on time.

PR08

The periodic review 2008 or PR08 was our assessment of the outputs that Network Rail (who manages the rail infrastructure in Great Britain) must deliver, and the levels of access charges paid by train operators for use of the infrastructure. It covers the five years running from April 2009 to March 2014, also known as control period 4 or CP4.

For more information see our section on periodic reviews.

PR13

The Periodic review 2013 or PR13 is our assessment of what Network Rail (who manages the rail infrastructure in Great Britain) must achieve for the next five year period, the money it needs to do so, and the incentives needed to encourage delivery and outperformance for the period from April 2014 to March 2019. This is also known as control period 5 or CP5.

For more information see our PR13 microsite.

PSRs

Permanent speed restrictions

PTEs

Passenger Transport Executives: bodies covering five of the six metropolitan counties in England charged with helping to integrate the use of public transport services, by ensuring that they meet the public’s needs and contribute to the wider social, economic and environmental wellbeing of local communities.

PUWER

Provision and Use of Work Equipment Regulations 1992