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STHC Process - Calculations & Factors Used

After measuring our "Pupil Home - School Distances" using spatial analysis we use various calculations and factors to generate the myriad of useful information contained in the standard STHC Analysis Output:-

Back to STHC Analysis Process ............ Continue to Reporting of Results

Pupil Home - School Distance

The starting point of our spatial analysis is to calculate the straight-line (“as the crow flies”) distance between the centre of a pupils home postcode area and the actual school they attend. In the STHC Output this is called the “Pupil Home – 'Actual' School Distance” or just "'Actual' Distance" for short. This represents the length of a single pupil journey from either home to school or back again, by the mode of travel recorded in the school census.

We also determine the nearest school that a pupil could attend given their national curriculum year (NCY), and measure the distance to that too. This is called the “Pupil Home – 'Nearest' School Distance” or just "'Nearest' Distance" in the output. Arguably this represents the "ideal world" scenario from a sustainable travel point of view - all pupils attending their nearest school. On a practical level as far as our analysis is concerned however, it gives us something to put the actual distances travelled by pupils into context. It puts a number to the reduction in overall "child miles" that is theoretically possible through "sustainable travel" measures alone given the current geographic distribution of schools and pupils (i.e. trying to change the travel choices made by the pupils rather than changing where they or the schools are). In other words it gives a quantifiable, and therefore directly comparable, measure of the current distribution of schools with respect to the pupils (or vice versa)!

So why do we use the straight-line distance rather than the distance of the route actually travelled? Well for start we don't actually know the route that the pupil will take to school. Yes you could make a good guess for those coming by car as they are driving along the roads, but are they coming by the "quickest" route or the "shortest" route? And what happens if they "park and stride", ie. park at a designated car park near the school and walk the rest of the way? And what about those that car share and so may not take the direct route to the school? As for those coming by bus, how far do they actually travel along the road? And what about those that may not be using the road at all? Walking and cycling paths are often not part of a road network, in which case we do not have the basic data that will enable us plot the route and therefore measure the distances involved. No it is much better to keep the spatial analysis process as simple and transparent as possible and make it consistent irrespective of the mode of travel involved, that way we can always be sure of comparing "apples with apples". Further, more complex analysis can always be undertaken using the GIS data included in the STHC Output if clients are so minded.

Note: In the STHC Output - in particular the Distance Stats spreadsheets and also the STHC School Report - we report both the minimum and the maximum "Pupil Home - 'Actual' School Distances" calculated. Unfeasibly long journeys for walking and cycling more than likely indicate miscoding of the original school census data - either the pupil postcode and/or the mode of travel - rather than super human pupils! Looking on the positive side, such errors would not have come to light unless spatial analysis had been undertaken so it is a necessary step to improving data quality for the future. We therefore simply encourage schools in this situation to try and ensure that any errors are corrected in time for the next school census.

Very occasionally a minimum "Pupil Home - School Distance" of zero is reported. This is an unavoidable consequence of using the centre of the postcode unit for the pupil location rather than the pupils actual home address. If a school does not have it's own unique postcode - and many smaller primary schools don't - it will be shared with adjacent houses. Thus any pupils attending the school from those houses will be shown as having a travelling distance of zero!

Walk Threshold Distance - This is the distance within which most pupils should "reasonably / realistically" be able to walk school. Although this is a simple enough concept to grasp, there is unfortunately no standard definition of what a "realistic" or "reasonable" walking distance is.

There is a "statutory Walking Distance" in England for the purposes of determining if a local authority is obliged to provide free home - school transport for a pupil. For a child who is under the age of 8, if the shortest available walking route bewteen their front gate and the nearest entrance of their nearest school is more than 2 miles (3.219 km), the local authority is obliged to provide free home - school transport. Similarly for a child who is aged between 8 and 16 whose walking route is more than 3 miles (4.828 km).

we have therefore had to define our own for the purposes of the STHC, one that can be consistently applied to all. When we first developed the STHC

as 800m for Primary age pupils and 2000m (2 km) for Secondary age pupils. This is broadly based on the 85th percentile "Pupil Home - Actual School Distance" measured by analysis - however see the Calculations section for more details.)

Note: As pupils attending 'Middle' and 'Special' schools cover both 'Primary' and 'Secondary' age ranges, both walk thresholds are shown on the maps for those schools but only the relevant one for the individual pupils age is used in the “within walk threshold” calculations. In certain circumstances West Berkshire Council, as the Local Authority (LA), has a duty to provide transport. Education Law details this duty and other discretionary powers that LAs have in considering transport provision when there is no duty to assist. LAs are also required to adopt and publish a Home to School Transport policy. The main purpose of school transport is to assist in enabling pupils to attend school. The Council aims to provide equitable, safe, efficient and cost effective transport to all entitled pupils in accordance with its duties and powers as provided for in legislation. This document sets out West Berkshire Council’s Home to School Transport policy and describes how the Council fulfils its duties and exercises its discretionary powers as required under legislation. The policy detailed here is determined in accordance with the relevant provisions of the Education Act 1996 and subsequent amendments by the Education and Inspections Act 2006.

Calorie Calculations For Walking & Cycling

These are based on the work of Roger Mackett, a professor of Transport Studies at University College London and one of the UKs’ leading researchers into the role of travel as a facilitator for children’s health:-

Primary Age Pupils

Mode of Travel Average Speed Calorie Burn Rate Calories Burned Per Km
Walk (WLK) 3.2 km/hour 1.85 cal/min 34.69 cal/km
Cycle (CYC) 16 km/hour 1.4 cal/min 5.25 cal/km

Secondary Age Pupils

Mode of Travel Average Speed Calorie Burn Rate Calories Burned Per Km
Walk (WLK) 3.2 km/hour 2.85 cal/min 53.44 cal/km
Cycle (CYC) 16 km/hour 2.15 cal/min 8.06 cal/km

Source: "The therapeutic value of children’s everyday travel" - Mackett, R.L., Lucas, L, Paskins, J. and Turbin, J. (2004). (URL:

Vehicular Travel Carbon Dioxide (CO2) Emission Calculations

These are based on the official UK government greenhouse gas conversion factors, first calculated by DEFRA (the UK Department for the Environment, Food and Rural Affairs) in 2007 as follows:-

Mode of Travel CO2 Emission Factor Per Km Reference
Car / Van (CAR)*
Taxi (TXI)*
0.2042 kg CO2/vehicular km
converted to
0.2042 kg CO2/passenger km
Table 6 – Combined average
for petrol & diesel cars
Car Share (CRS)*
0.2042 kg CO2/vehicular km
converted to
0.1021 kg CO2/passenger km
Table 6 – Combined average
for petrol & diesel cars
Public Service Bus (PSB)
Dedicated School Bus (DSB)
Bus Type Not Known (BNK)
0.0891 kg CO2/passenger km Table 8 – Bus
Train (TRN)
0.0602 kg CO2/passenger km Table 8 – National rail
Metro/Tram/Light Rail (MTL)
0.0650 kg CO2/passenger km Table 8 – Light rail & tram
London Underground (LUL)
0.0526 kg CO2/passenger km Table 8 – London Underground

Source: ‘“Greenhouse Gas Conversion Factors For Company Reporting”, DEFRA (2007). (URL:

*Note: The 2007 DEFRA figures quote the carbon emmission factor for "Cars / Vans" in terms of kg CO2 per vehicular kilometre, whilst all the others are for passenger kilometres.

DEFRA first published an official list of emission factors in 2007, which was the same time as the STHC was being launched as a generally available service to all local authorities. Thus we adopted the DEFRA figures to calculate the school travel carbon footprints for the STHC. Since then however DEFRA have revised the figures just about every year as the science behind determining and measuring all the individual factors involved in greenhouse gas emmissions has improved. With each revision however the calculation of the factors has become more complex, and not every factor is revised each time. To keep things simple therefore, and to enable "like-for-like" comparison between analysis years, we have continued to use the original 2007 figure in our STHC carbon footprint calculations. Figures for each revision are still available on the DEFRA website however so we invite you to investigate further, perhaps as a classroom project, to see what difference these revisions make to the calculated carbon footprint figure for your school.

Click on the following links to download each revision of the official DEFRA figures as an Adobe Acrobat (.pdf) document from the DEFRA website. The relevant figures are found in Annex 6: Passenger Surface Transport Emission factors in each document 2007, 2008, 2009, 2010, 2011, 2012

Overall STHC Sustainable Travel ("RAG") Ratings For Schools

To help schools and school travel professionals get an immediate indication of how an individual school compares to the others in the authority in terms of sustainable school travel, as well as giving them a start on setting SMART (Sustainable, Measurable, Attainable, Reasonable & Time-bound) targets to do something about it, we devised a simple traffic light system (ie. results coded as either "Red", "Amber" or "Green") of STHC Sustainable School Travel Indicators:-

  • Number Pupils Within a Realistic Walk Threshold Coming by Car" - is the short term indicator in that it is something that can be immediately tackled by the school itself if it put its mind to it with the help of the school travel professionals - awareness raising campaigns like Walk Once a Week (WOW), "Park & Stride" schemes, better cycling / pedestrian infrastructure etc. It is also a concept that everybody can understand ("why are they not walking when it's such a short distance?"), and therefore buy into the idea of tackling. From our point of view it also is something that can be easily and consistently measured, and so it is obvious if progress is being made in tackling the issue or not.
  • Amount of CO2 Per Pupil Travel Emissions Compared To The Authority Average - is a longer term indicator because, although the concept is fairly easy to understand - the further you drive the more CO2 is produced - tackling the issue is not so straight forward and there is no single, easily understood target that everybody can immediately work towards. Any progress will require sustained action over a longer period of time. From our point of view it also is something that is more difficult to measure.

These indicators were devised in consultation with client authorities when the School Travel Health Check service first started. We started out with just the CO2 indicator but it soon became clear that there are some contributing factors that are beyond a schools control, and therefore this would undermine any efforts to make any progress on improving sustainable school travel if this was the only measure of progress. For example the geographic fact that a school is rural often dictates that pupils will have to travel a greater distance and from a wider catchment area where a car or school bus are the only available options, which will result in a larger carbon footprint per pupil for the school journey (= Amber or Red Long Term Indicator). There is very little a school can do to change this reality, but this shouldn't stop them from raising awareness on the issue within their school community and working towards goals that are meaningful to them.

However it is also clear that indicators cannot tell the full story in isolation and need to be considered in conjunction with other data. For example for our same rural school it is often the case that there are very few (if any) pupils living within the walk threshold and so it would probably get a Green Short Term Indicator. However we've already seen that pupils will come from further away so the carbon footprint will be higher, but even this is not straightforward. Intuition dictates that it would be better if the pupils were travelling by bus but what if most of them were being bussed in from a considerable distance away, perhaps from the edge of the nearest large settlement, to boost school numbers? Is that better than kids travelling by car on a more individual basis from a much shorter distance?

We are continually consulting with out clients and the wider school travel community on how our indicators could be improved to help schools work towards more sustainable travel.

Driving Costs

In the STHC School Report we translate distances travelled by car into driving costs. The factor used comes from the UK Automobile Association (AA), who have been calculating the "true cost" of motoring to the British motorist (ie. taking into account the standing and running costs such as fuel, depreciation, tax, insurance, maintenance costs etc.) since 1950. For 2011 the combined average for petrol and diesel cars, costing under £12,000 when new and driving approximately 10,000 miles per year, is £0.27 per km (£0.43 per mile).

On the AA website you can look at the "true cost of motoring" figures going back to 1998 (use the drop down list on the right hand side)

Source: The Automobile Association (URL: