PTAL stands for
Public Transport Accessibility Level. It is a method sometimes used in
United KingdomThe United Kingdom of Great Britain and Northern Ireland is a sovereign state located off the northwestern coast of continental Europe. It is an island country, spanning an archipelago including Great Britain, the northeastern part of Ireland, and many small islands...
transport planning to assess the
access levelAccessibility is a general term used to describe the degree to which a product is accessible by as many people as possible. Accessibility can be viewed as the "ability to access" the functionality, and possible benefit, of some system or entity...
of geographical areas to public transport.
PTAL is a simple and easily calculated approach which hinges on the distance from any given point to the nearest public transport stops and the frequency of the service from those stops. The final result is a grade from 1-6 (including sub-divisions 1a, 1b, 6a and 6b) where a PTAL of 1a indicates extremely poor access to the location by public transport, and a PTAL of 6b indicates excellent access by public transport.
The PTAL calculation was originally developed by the
London Borough of Hammersmith and FulhamThe London Borough of Hammersmith and Fulham is a London borough in West London, and forms part of Inner London. Traversed by the east-west main roads of the A4 Great West Road and the A40 Westway, many international corporations have offices in the borough.-History:The borough was formed in 1965...
, and was later adopted by
Transport for LondonTransport for London is the local government body responsible for most aspects of the transport system in Greater London in England...
as the standard method for calculation of public transport access in
London[]London is the capital of England and the United Kingdom. It has been a major settlement for two millennia, and the history of London goes back to its founding by the Romans, when it was named Londinium. London's core, the ancient City of London, the 'square mile', retains its medieval boundaries...
.
PTAL stands for
Public Transport Accessibility Level. It is a method sometimes used in
United KingdomThe United Kingdom of Great Britain and Northern Ireland is a sovereign state located off the northwestern coast of continental Europe. It is an island country, spanning an archipelago including Great Britain, the northeastern part of Ireland, and many small islands...
transport planning to assess the
access levelAccessibility is a general term used to describe the degree to which a product is accessible by as many people as possible. Accessibility can be viewed as the "ability to access" the functionality, and possible benefit, of some system or entity...
of geographical areas to public transport.
PTAL is a simple and easily calculated approach which hinges on the distance from any given point to the nearest public transport stops and the frequency of the service from those stops. The final result is a grade from 1-6 (including sub-divisions 1a, 1b, 6a and 6b) where a PTAL of 1a indicates extremely poor access to the location by public transport, and a PTAL of 6b indicates excellent access by public transport.
Background
The PTAL calculation was originally developed by the
London Borough of Hammersmith and FulhamThe London Borough of Hammersmith and Fulham is a London borough in West London, and forms part of Inner London. Traversed by the east-west main roads of the A4 Great West Road and the A40 Westway, many international corporations have offices in the borough.-History:The borough was formed in 1965...
, and was later adopted by
Transport for LondonTransport for London is the local government body responsible for most aspects of the transport system in Greater London in England...
as the standard method for calculation of public transport access in
London[]London is the capital of England and the United Kingdom. It has been a major settlement for two millennia, and the history of London goes back to its founding by the Romans, when it was named Londinium. London's core, the ancient City of London, the 'square mile', retains its medieval boundaries...
. It is not commonly used outside
Greater LondonGreater London is the top-level administrative subdivision covering London, England. The administrative area was officially created in 1965 and covers the City of London, including Middle Temple and Inner Temple, and thirty two London boroughs...
or the south east of England.
Method
The first stage in PTAL calculation is to calculate the walking distance from the site (known as the
point of interest (POI)) to the nearest
busA bus is a road vehicle designed to carry passengers. A bus seats a maximum of 8 to 300 passengers...
stops and
railRail transport is the conveyance of passengers and goods by means of wheeled vehicles running along railways or railroads. Rail transport is part of the logistics chain, which facilitates international trade and economic growth...
stations (where rail can be taken to also include
London UndergroundThe London Underground, Underground or Tube is a rapid transit system serving a large part of Greater London and neighbouring areas of Essex, Hertfordshire and Buckinghamshire in the UK. The first section opened in 1863, and was the first underground railway system in the world, and, starting in...
,
DLRThe Docklands Light Railway is a light metro or light rail system opened on 31 August 1987 to serve the redeveloped Docklands area of East London, England...
and trams). These stops and stations are known as
service access points (SAPs)'. Only SAPS within a certain distance of the POI are included (640m for bus stops and 960m for rail stations, which correspond to a walking time of 8 minutes and 12 minutes respectively at the standard assumed walking speed of 80m/min).
The next stage is to determine the service level during the morning peak (defined as 0815-0915) for each route serving a SAP. Where service levels differ in each direction on a route, the highest frequency is taken. On railways, a route is generally defined as a service with a particular calling pattern - for example, services on the
Piccadilly lineThe Piccadilly line is a line of the London Underground, coloured dark blue on the Tube map. It is the third busiest line on the Underground network judged by the number of passengers transported per year. It is mainly a deep-level line running from the north to the west of London via Zone 1, with...
from
HammersmithHammersmith is an urban centre in the London Borough of Hammersmith and Fulham in west London approximately 5 miles west of Charing Cross on the north bank of the River Thames...
could be divided into two "routes": Cockfosters to Heathrow and Cockfosters to Uxbridge.
A
total access time for each route is then calculated by adding together the walking time from the POI to the SAP and the average waiting time for services on the route (i.e. half the
headwayHeadway is a measurement of the distance between vehicles in a transit system. The precise definition varies depending on the application, but it is most commonly measured as the distance from the tip of one vehicle to the tip of the next one behind it, expressed as the time it will take for the...
). This is converted to an
equivalent doorstop frequency (EDF) by dividing 30 (minutes) by the total access time, which is intended to convert total access time to a "notional average waiting time, as though the route were available at the doorstep of the POI".
A weighting is applied to each route to simulate the enhanced reliability and attractiveness of a route with a higher frequency over other routes. For each mode (e.g. bus, Tube, DLR, tram, rail), the route with the highest frequency is given a weighting of 1.0, with all other routes in that mode weighted at 0.5.
Finally, the EDF and the weighting are multiplied to produce an
accessibility index for each route, and the accessibility indices for all routes are summed to produce an overall accessibility index for the POI.
This accessibility index (AI) can then be converted to a PTAL grade (1-6) through a banding system (where AIs 0.00-5.00 are PTAL 1, 5.01-10.00 are PTAL 2, etc up to PTAL 6 for scores of 25 and above).
Uses
The PTAL is used as a development planning tool in London to determine both permitted parking standards and development densities. Developments of large sites (i.e. those which the London boroughs must refer to the
Greater London AuthorityThe Greater London Authority is the city-wide governing body for London, England. It consists of a directly-elected executive Mayor of London, currently Boris Johnson, and an elected 25-member London Assembly with scrutiny powers.-Purpose:...
are subject to planning guidelines which allow higher levels of parking in areas with low PTALs (i.e. poor public transport) and vice versa, and which also relate the allowed density of development to PTAL (i.e. areas better served by public transport can have higher density housing or offices).
TfL also have software to calculate PTALs across wide areas using GIS and timetable data, the typical result being a map with coloured bands relating to PTAL grades.
Advantages & disadvantages
Whilst PTAL is a simple calculation (easily performed by a spreadsheet) that offers an obvious indication of the
density of public transport provision in an area, it suffers two key problems:
- It does not take into account where services actually go to - for example, a bus that runs every ten minutes to the bottom of the road is considered better than a bus that runs every twelve minutes to the city centre.
- The use of arbitrary cut-offs to exclude more distant service access points underestimates the ability to access locations just outside those cut-off distances. For example, a point 960m from King's Cross could have a PTAL of 6, whilst a point 961m from the same station could have a PTAL of 1 or 2.
Accessibility modelling has been proposed as a solution to these problems. It uses GIS to calculate door-to-door travel times by public transport to a grid of points around the point of interest, resulting in a set of isochrones - journey time contours - within which the number of workplaces, households or residents can be calculated using
censusA "census" is the procedure of systematically acquiring and recording information about the members of a given population. It is a regularly occurring and official count of a particular population.In other words every 10 years...next one would be in 2010 The term is used mostly in connection with...
data. This method takes into account many more factors than PTAL, but is much more time-consuming and requires expensive software.
External links