PTAL: public transport accessibility level in London

PTAL stands for public transport accessibility level, and the ptal meaning planning teams care about is narrow: it is a Transport for London measure of how close a point is to public transport stops and how often services run from them. Nothing more. It says nothing about where those services go, how crowded they are, or how long your journey takes once you board.

Understanding that limitation is what stops a PTAL figure being used badly, and it is used badly often.

What the bands mean

Scores run from 0 to 6b, with several bands split into a and b:

Central London and the areas around major interchanges reach 6a and 6b. Much of outer London sits at 2 or 3, and pockets of 0 and 1 exist within a few miles of a town centre where the walk to a stop crosses a railway line or a main road with no crossing.

The bands are derived from a continuous access index, so a site scoring at the top of band 3 and one at the bottom of band 4 are almost identical in reality. Quoting the index value alongside the band is more honest than quoting the band alone, and it is the number to use where a site sits near a policy threshold.

How the score is worked out

The method is public and it is worth understanding, because it explains why scores change.

Walk access time is calculated from the assessment point to nearby stops, using a standard walking speed and separate distance thresholds for bus stops and for rail, underground and light rail stations. Anything beyond the threshold is excluded entirely, so a station 15 minutes away contributes nothing at all rather than contributing a little.

For each service at each stop, an average waiting time is derived from the scheduled frequency, with an added allowance for reliability. Walk time and wait time combine into a total access time, which is converted into an equivalent doorstep frequency. The highest scoring route in each mode is counted in full and the remaining routes at half weight, which prevents a stop served by six near-identical bus routes from scoring six times over.

Those weighted frequencies are summed into an access index, and the index is banded. So a timetable change alters the score without anything being built, and a bus route withdrawal can move a site down a band between the feasibility study and the application.

Where to look the score up

Transport for London publishes the connectivity assessment toolkit, which returns PTAL for any point in Greater London along with travel time mapping, and the underlying data is also published on the London Datastore. Borough planning teams use the same source.

Two practical points. Record the date of the calculation and the version of the base data in your report, because a reviewer will check it against the current figure and a mismatch looks like error. And calculate PTAL at the point people actually leave the building, which on a large site can mean several assessment points rather than one at the site centroid.

Where a scheme is phased and a new bus service or station is committed, the toolkit allows a future year assessment. Use it, and state clearly what is assumed and on what authority, since an uncommitted service is not evidence.

How the London Plan uses PTAL

Two areas of the London Plan 2021 lean on it.

Parking is the first. The Plan sets maximum residential parking standards that vary by PTAL band and by location within London, with car-free development expected in the most accessible locations and in the central activities zone. A site's band therefore determines the parking ceiling before any local standard is applied, and it is the number a highway officer looks at first.

Density is the second, though less mechanically than under earlier plans. The current Plan takes a design-led approach to optimising site capacity rather than reading density off a matrix, with public transport connectivity and access to services among the factors considered. PTAL is evidence in that assessment rather than the answer to it.

Boroughs add their own layers, and some apply local parking standards or cycle parking requirements keyed to PTAL bands in their own local plans. Check the borough policy as well as the London Plan.

Blue badge parking sits outside the maximum standards and has to be provided regardless of band. That catches schemes which describe themselves as car free and then have nowhere to put the accessible bays, and it is a straightforward reason for a highway officer to ask for a revised layout late in the process.

What PTAL does not tell you

Four things, all of which come up at committee.

It does not measure destination. A site with two frequent bus routes that both terminate locally can score the same as one with a route to a major interchange, and residents do not travel to bus stops for their own sake.

It does not measure crowding or reliability beyond the standard allowance, so a station at capacity in the morning peak scores as well as an empty one.

It does not account for severance. The walk threshold is a straight distance converted to time, and it does not know about the railway embankment, the dual carriageway or the absence of a crossing.

And it says nothing about step-free access, which matters for a scheme aimed at older residents or for accessible housing.

Where any of those points is relevant, use the travel time mapping in the same toolkit to show journey times to named destinations. That evidence answers a committee question that a band cannot.

Using PTAL in a transport submission

For most London schemes the accessibility evidence sits in a Transport Statement or, above the relevant thresholds, a full transport assessment. Set out the band, the access index, the calculation date, the assessment points and the stops and services included, then explain what follows for parking and trip generation.

Trip generation is where the two connect. Mode share assumptions drawn from a trip rate database should be sense-checked against the accessibility of the site, and where the assumptions come from TRICS trip rates the comparison sites should have similar public transport provision. A suburban comparison site applied to a PTAL 6a location will overstate car trips, and the reverse understates them.

Where a scheme proposes reduced parking on accessibility grounds, expect the borough to ask for on-street evidence as well. A Parking Survey carried out to the established overnight methodology shows what the surrounding streets can absorb, and a PTAL band on its own rarely persuades a residents association.

If the scheme relies on behaviour change rather than physical provision, a Travel Plan with measurable targets and monitoring is the mechanism, and it will usually be secured by agreement.

PTAL is a London measure. Outside Greater London, accessibility is assessed through local methods, usually a combination of walking distances to bus stops and stations set out in the local plan or a parking standards document, and importing a PTAL figure into an application elsewhere invites an obvious question about relevance.

One honest caveat. A band is a snapshot of the network as timetabled, and bus frequencies in outer London have moved in both directions over recent years. Where a permission is likely to be implemented several years after it is granted, say so in the report rather than presenting the score as a fixed property of the site.

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