Monitor Children’s walking behaviour in the local environment

-using GPS and energy expense monitors

Yi GongCentre for Advanced Spatial AnalysisUniversity College London, UK

Outline:

• Introduction

• Background of this study

• Research Methods

• Data Analyse

• Future work

• Introduction

• Definitions – Physical activity and its intensity (light, moderate and

vigorous)– Active transportation / active travel / active commuting

To understand children’s currently use of the local environment

To make it easy for children to move around on foot.

Monitoring children’s walking in local environment

• Background of this study– The decrease of children’s physical activity and its

healthy impact – Children’s needs to be outdoors and active travel

Background 1• The decline of children’s physical activity levels are found in the modern society, which

parallels with the increase of obesity and sedentary activities. Lack of physical activity increases the risks on poor health and lack of well-being in children and adults.

• The recommendation for physical activity from British Department of Health’ is – children and young people should have one hour of moderate intensity physical activity each day.

• In order to achieve the recommended levels of activity, the young child are also suggested to attend the following activities (The UK 2000 time use survey 2003). They are:

– Daily walk to and from school– Daily school activity sessions (breaks and clubs)– 3-4 afternoon or evening play opportunities– Weekend: longer walks, visits to park or swimming pool, bike rides

The reasons for decline of physical activity on children

• The children of today are more likely to be indoors. Significantly fewer young children are allowed out alone.

The value of children’s access in neighbourhood• Simply spending time outdoors promotes physical activity. studies have

shown that children who spend the most time outside are the most active.

When being outdoors, children• Get exercise, engaging with health prompting, to be more active• Get an opportunity to explore and learn the environment – physical and

social

Especially when without adults, children • Learn to make independent decisions• Learn to explore and find their way around• Learn to play and share experience with peers, establish their own

relationships

• Children travel by car by many short trips while walking less than before. Children in household with cars walked about a third less than children in household without cars.

• Local environmental factors limits children’s mobility in local environment. For example, child’s road safety are the most concerns and barriers for children move around on foot. Hillman (1991) state that space within which children can move freely shrinks significantly as street traffic increases in the immediate environment

Thus, there is an increasing recognition of children’s needs in local environment, where they can meet their peers and play. Streets and open space are better for children are also likely to be better for other pedestrians.

The reasons for decline of physical activity on children

Walking does matter on childrenWalking has been focused, both because of environmental reasons and the concern for the children’s health

–It is the oldest and perhaps the most environmental friendly and healthy form of transport. –It bring real health benefits to travellers by providing regular excises. walking / cycling itself is classified as moderate intensity physical activity. Personal daily physical activity levels thus can be built up by regular active commuting –The interaction of local environment is also an important arena for children in terms of social interaction and learning process. –more walking means less use of motorized transport. This can help to ease traffic congestion, reduce air pollution, and enhance a sense of community.

–The most common purpose of walking trips by children is to travel to and from school.

–Studies show that walking to school is positively correlated with children’s physical activity levels. For example, (Tudor-Locke et al. 2003), (Sirard et al. 2005) ,(Mackett et al. 2005), (Cooper et al. 2003b)

–Put children into the car instead of letting them walk on their own feet, which seems to be part of an “evil” circle. More children travel by car, lead to more traffic in the areas where children like to go, which in turn forces parents to escort their children because of increased traffic.

Initiatives on active travel As walking can incorporate transport as a means for physical activity into daily routine, active commuting has been globally identified as a potential source of regular moderate-intensity activity and an opportunistic target for intervention. Such as “walking bus”, “work in to work out”.

To understand children’s currently use of the local environment

To make it easy for children to move around on foot.

To know • What kind of travel that children make

on foot• Where they walk to? • Which route they choice to walk ? • Who go with them? • Where do they become more active?

Monitoring children’s walking in local environment

• Research Methods– Measuring energy expense– Tracking children’s walking behaviour

Study Methodology – measuring physical activity

• Observation, questionnaire, interview, self-report, cross-sectional survey– The difficulty is to quantitatively measure physical activity by those methods, as

the physical activity comprised all sorts of behaviour in different locations over the time. Thus, researchers either adopt a qualitative approach, focusing on the collection of textual data from in-depth interviews or superficial data from large-scale surveys.

– Neither of them can offer a very accurate statistical result to measure occupational, household and transportation-related physical activity

• Pedometers, heart monitors, monitors and accelerometers– The applications are relatively new and mainly appear since the middle of 1990s,

and those new equipments offer a much more accurate measurement– Accelerometers provide objective and detailed measurements of the frequency,

duration and intensity of activity and can be used over relatively long periods by children

– pedometers can provide an objective indicator of step counts, a marker of total volume or duration of activity

• Quiet high percentage of data lost or uncompleted when fitting the accelerometers on children have been reported in previous studies. This is due to technological failure and the nature of children.

Study Methodology – travel behaviour research 1

• focus groups, interviews, questionnaires, travel diary – Respondents often use a written dairy or log to record their trips’ details – Those qualitative methods have been used on large population-based studies

(Transport Statistics Bulletin: National Travel Survey 2002 2004).

– in those traditional survey methods, some trips have been underreported. This non-response may because of participants’ memory decay, failure to understand or to follow survey instructions, unwillingness to report full details of travel, and simple carelessness

– Because those survey trip data is the primary data, those non-reported trips might have potentially serious impact on the research results (Wolf 2003)

Study Methodology – travel behaviour research 2

• GPS tracking– Employ Global Positioning System (GPS) to collect

second- by- second location, position and speed data during the travel journey.

– GPS loggers can record the location at certain intervals, and create a track file or log of activities.

– Active and passive GPS loggers, vehicle-based and personal-based (on-body ) loggers

(xi, yi, zi. ti ) i =1..4

GPS satellite positions

(X-xi)2 + (Y- yi)2 + ( Z-zi)2 = li 2

= C2 * (T- ti)2(X, Y, Z, T)

Study Methodology – travel behaviour research 3• In travel behaviour research, GPS-based tracking adds a new spatial dimension to

trip-making data by tracking actual route choice. it effectively reduces the underreporting and misreporting trips, compared with the traditional self-reported methods. it provides great insight into details from trip’s origin to destination.

• Although GPS loggers provide a considerable increase of accurate location data, those data does not reveal any other information, such as trip purpose, trip accompany and so on. Other traditional qualitative methods have been introduced in conjunction with GPS loggers to obtain more additional details and a better understanding of the location data

• Basic household socio-economic data, trip purpose and habitual destination address can be obtained through interviews, questionnaire and so on, Also, GPS loggers have been tested to work with PDA or CATI.

• The advantage of using GPS– The reduction (or even elimination) of respondents’ burden– The availability of path choice information– The high level of spatial accuracy– The fact that data is generated in digital format which allows direct analysis

• The disadvantage of GPS – The limits on accuracy, the possibility to lost signals and high cost.

Study Methodology – travel behaviour research 4

Post processing of GPS data– Filtering

• removing unlikely locations data to increasing the location accuracy

– Interpolating: address the problem of uneven sampling. • Interpolating can provides locations that are equally spaces in

time. • When tracking is combined with other equipments or methods in

order to obtain other information (i.e. environmental / behavioural parameters), those instruments generally have sampling rates that differ from the GPS loggers. Thus, by interpolating tracking data, each measured parameter can be matched to an estimated location.

Outline:

• Data analyse – GPS data handling– Link GPS data with energy expense data– Link children’s walking behaviour with land use data

• Questionnaires surveys of children and their parents

• Monitoring children over a period of 4 days with– RT3 to estimate energy expense

every minut

– GPS loggers to record spatial location data –Garmin GPS Foretrex 201:

• 2.75oz in weight, • 8.38 cm( W) 4.32cm (H) 1.52cm (D)

Research methods:

200 children aged 8 to 11 years old in Cheshunt

•Travel diary record trip purpose, transport mode, accompany status and etc.

Research Methods

walked15:30

Peter’s house

18:40

19:00car

From survey data:Sample children’s access to local environment with active travel• Percentage of children who have access to park, garden

• Percentage of children allowed to walk alone, to take bus alone, to bike alone and to cross the main road.

• Places that children are allowed out alone

– Local shops, shopping centres, cinema, sport facilities

94%

52%

73%56%

34%43%

83%

58% 63%51%

34%21%

0%

20%

40%

60%

80%

100%

access togarden

access to park allow ed to crossmain road alone

allow ed to w alkalone

allow ed to takebus allone

allow ed to bikealone

boy girl

29%

10%

29%

17%

29%

16%

29%

16%

0%

5%

10%

15%

20%

25%

30%

35%

go to local shopalone

go to cinema alone go to park alone go to sport centrealone

boy girl

One child one day

Sum of children’s active level (when GPS working) each day

Sum of children’s active level each day.

RT3 data and Travel diary

Raw GPS data

Based on the shortest distance between two points should be less than the distance travelled at the maximised speed in that period plus twice of the GPS accuracy allowance (20 meters), and time interval between two points, Our algorithm uses following criteria in order to remove those unlikely locations.

Criteria 1: exclude the data not from the targeted research period ( i.e. data from Monday, Tuesday and Wednesday)Criteria 2: exclude the data which beyond the distance at the speed of 140Mile/Hour during the time interval, plus

40 meters GPS accuracy allowance.Criteria 3: exclude the point at the beginning of the trip, which has long time interval with the previous point (>5

minutes) and the speed of the following point is larger than 100Mile/Hour.Criteria 4: exclude the data which has less than 5 minutes interval with the previous, while the following point has

the speed is over 100Mile/Hour

Although, the maximised speed is that 70mph on UK highway, people do drive faster on the motorway. For example, see the blue points in the following map are all over 80mph. In order to ensure that we did not filter those useful points, we double 70 mph into 140mph.

Filtering GPS data

Where children playing?

Where children walking?

Based on a given set of filtered location, independent of their actual accuracy, we interpolate children’s walking traces on the time interval of 1 minute, so that we can link GPS location data with RT3 energy expense data which also has 1 minute interval. The way we use to calculate the point which best present a set of GPS points are:

1> Starting from the first completed minute each trip, which means that the minute is the first minute with more than 1 point, as well as at least 1 point is from the first half of that minute. Within this minute, average speed on east/north is the distance difference divided by second difference. The arithmetic average of easting/northing is related with the average number of seconds. Following the same direction, the interpolation point will be arithmetic average of easting/ northing plus the distance travelled between the 30 and the average number of seconds. For example, in the following data, the 52nd minute is the first completed minute. Thus, the first interpolation point’s easting can be get as

the arithmetic average of easting = (53475.19+534752.6+534741.9+534719.8)/4the distance difference within this minute = 534719.8-534751.9the seconds difference = 47- 02=45the average speed on east = (534719.8-534751.9) /45the new easting = the arithmetic average of easting -the average speed on east

*(45-30)

Interpolation of GPS 1

1

2

2> After the first completed minute, the difference between minutes will be considered. The average speed on east/north can be calculated from the difference between the arithmetic average of easting/northing and the interpolation point in previous minute divided by time difference. Following the same direction, the interpolation point will be the easting/northing from previous interpolation point plus the distance travelled in the average speed on east/north under regular time interval

3>If the first completed minute is not the first minute of that trip, those points will be interpolated backwards from the first complete minute as the step 2.

for example, in the 53rd minute, the arithmetic average on easting = (534699.8+534682.3+534656.8+534631.1)/4the speed on easting = (the distance between the arithmetic average on easting in 53rd

minute – the interpolation point in 52nd minute) / (average seconds in 53rd + 30)the interpolation of easting in 53rd minute = the interpolation easting in 52nd minute + speed

on easting *60

Interpolation of GPS 2

1

2

Sample GPS data

Raw GPS Filtering GPS

Interpolated GPS points with 1 minute interval

Visualize the energy expense in space

Energy expense

Walking traces with energy expense

Physical activity level

Walking traces with energy expense

Future work• Link with land use data - OS

MasterMap Topography layer

• How many energy has been expensed by different children on different land uses?

• Whether the energy intensity varies on different land use or not?

• How many percentages of travelling time takes place on each type of land use?

• Whether the types of land used on the way to school is different from school to home?

• Whether the time spent on different land use on way to school is different from school to home?

Future Work

• Geo-visualisation– Space- time path Energy, space and time path

• Modelling children’s walking- correlated random walk – the tortuousity of walking path, – path length, – move length , – move duration, – speed, – Turning angle, – Turning rate, – Net displacement

THANK YOU!

Many thanks for Roger Mackett, James Paskins, Belinda Brown, Mike Batty, Kay Kitazawa,