East Oxford Low Traffic Neighbourhood – Sensors and data
analysis methodology
Vehicle, cycle and pedestrian counts
LTNs boundary roads (those roads immediately
surrounding the LTN area) and some of the roads inside
the LTN area, have been monitored by VivaCity object
identification sensors. These sensors count and classify
a variety of road users including cars, pedestrians and
cyclists, using machine vision. No personal data is
collected, and the raw images of the camera are not
used.
There has been a growing network of VivaCity sensors
in and around Oxford for several years. The locations of
the particular cameras used for the East Oxford LTN
survey are shown in figure 2 for boundary roads and
figure 3 inside the LTN, below. Counts from these
sensors are made across ‘count lines’ which reflect the
direction the sensor is facing.
Figure 1 - VivaCity sensor
Figure 2 – VivaCity sensor locations for East Oxford LTN Boundary Roads
The count lines of these boundary road locations are:
OX20_Iffley_Rd_North
OX36_St_Clement_west
OX38_Iflley_Road_North
OX39_Cowley_road_north
OX44_Cowley_Rd_East
S107_morrellAve_road_occ001
S107_morrellAve_pathLHS_occ001
S107_morrellAve_pathRHS_occ001
Figure 3 – VivaCity sensors locations for East Oxford in-LTN Area
The count lines at these in-LTN area locations are:
OX44_Divinity_Rd_North
OX44_Divinity_Rd_North_Peds_Crossing
OX44_Divinity_Rd_North_Peds_LHS
OX44_Leopold_St_West
Data analysis methodology
To evaluate the
difference of the LTNs on traffic volume, the percentage change in
traffic volume on in-LTN and boundary roads will be calculated by subtracting the data
from the pre-implementation period (20 November 2021 to 19 May 2022) from the
post-implementation period, (starting 20 May 2022).
An
impact estimate is calculated to help account for variation in traffic flows over time
from other external influencing factors and general trends such as travel to work
behaviours. To do this we calculate the
difference in the control areas in the same way
as above. Once calculated we subtract the control
difference from the intervention
difference, creating the
impact estimate. It is calculated for each mode (cars,
pedestrians or cyclists) separately.
A further
adjusted impact estimate is calculated to account for seasonal or control area
bias. To calculate the
adjusted impact estimate we extend the difference calculation
above by using data from 2019. This is done by firstly subtracting the pre-
implementation intervention area data (20 Nov 2021 to 19 May 2022) from the post-
implementation intervention area data (20 May 2022 onwards) and then repeating the
process for 2019, from which an average is taken from the resulting outputs. This
process is then further repeated for the control areas, before making a final
adjusted
impact estimate calculation by subtracting the extended intervention area difference
from the extended control area difference.
Control sites are similar roads in Oxford to those in and around the impacted LTN, that
would have experienced minimal impacts attributable to the LTNs and where sensor
data was available. The sites are:
OC2_Ashhurst_Way_West
-
Control site for in-LTN measurements
OX11_Bayswater_Rd_East
-
Control site for LTN Boundary Road measurements
OX13_B4495_South
-
Control site for LTN Boundary Road measurements
OX15a_Headley_Way_South
-
Control site for in-LTN measurements
OX25b_London_Rd_West
-
Control site for LTN Boundary Road measurements
OX27_Minns_Business_Park
-
Control site for in-LTN measurements
OX31b_Marston_Ferry_Rd_East
-
Control site for LTN Boundary Road measurements
OX31c_Banbury_Road_South
-
Control site for LTN Boundary Road measurements
OX31c_Moreton_Rd_West
-
Control site for in-LTN measurements
OX49_Woodstock_Rd_North
-
Control site for LTN Boundary Road measurements
VivaCity sensor count data
A file of raw data for VivaCity count lines from 20 November 2021 to 19 May 2022 for
East Oxford LTN monitoring and evaluation is embedded below. When we make our
analysis we will undertake a validation process on all data to ensure any anomalous
readings are identified and discounted.
East Oxford LTN VL
raw data Nov2021-May 2022.csv
VivaCity sensor data may also be seen by visiting this site,
Oxbike.co.uk which uses
feeds from all the VivaCity sensors in and around Oxford.
Additional traffic surveys within the East Oxford LTN area
Because monitoring and evaluation work began under
Emergency Active Travel
Regulations, we necessarily made use of existing VivaCity sensors. However, there
are few of these inside the East Oxford LTN area so we undertook additional
Automatic Traffic Count surveys at 10 sites for one week in November 2021 for
vehicles and cycles - their locations are shown in figure 4. ATCs use pneumatic
tubing across a road to count air pulses from passing traffic and they can determine
flow rate, mean speed and class of vehicle (including cycles). These sites will be
surveyed again in November 2022 (and November 2023), so providing a simple
measure of the change in vehicles and cycle traffic. Impact estimates and adjusted
impact estimates as calculated for the VivaCity sensors cannot be calculated for
these sites as control data is unavailable.
Figure 4 - Locations for ATC surveys (bright blue markers) - East Oxford LTN
Two further surveys have been undertaken within East Oxford LTN; these also use
ATCs but with additional CCTV surveys. These CCTV surveys will provide the
pedestrian count that ATCs can’t; they also provide confirmation of cycle counts.
These were undertaken in October 2021 and also at control sites in Jericho:
Observatory Street and Farndon Road. Control sites allow the calculation of impact
estimates. All these surveys will be repeated in October 2022 (and October 2023).
Figure 5 - Locations for ATC surveys with CCTV pedestrian counts (bright blue location markers) - East Oxford
LTN
Air Quality
Air quality is monitored using diffusion tubes, typically
mounted on lamp posts. They measure the
concentration of Nitrogen Dioxide and are extensively
used by local authorities for longer term air quality
sampling. There are many such sensors in Oxfordshire
and analysis is undertaken by Oxford City Council. The
tubes are changed monthly and sent to an external
laboratory for analysis. Data is bias corrected and
annualised as pe
r LAQM TG16 requirements. More
information and air quality data can be found on the
publically available website
Home (air-quality.info). The sensor locations used for East Oxford LTN air
quality monitoring are shown in figure 7 below.
Figure 6 - Typical installation of a
diffusion tube
Figure 7 - Air Quality monitoring locations, 2021 - East Oxford LTN
Data for 2021 is published in the
Air Quality Annual Status Report and is also
available for earlier years for sensors prefixed ‘DT’ in the map above. Please note,
data for 2022 will be published in early 2023 following ratification.
Data analysis methodology
The following methodology for analysis of air quality is proposed:
• We must wait until the end of 2022 so that we can have the full ratified dataset
for the year for the monitoring sites
• Control sites with existing sensors will be identified that it is reasonable to
assume have not suffered from any direct traffic intervention during 2022
(from the LTN, or other factors)
• The annual levels obtained will be compared at those control sites in 2021
and in 2022
• If levels in the control sites remain much the same between years, then it is
reasonable to conclude that the effect caused by the pandemic have
stabilised, and hence we can just directly compare the annual arithmetic
mean of 2021 and 2022 at the sites of interest to the LTNs and assume any
differences are due mostly to the impacts of the LTN trials
• However, if the levels at the control sites chosen are significantly different
between the years 2021 and 2022 and consistent between the several control
sites selected (same level of increase or decrease observed in different
control sites), then we would discount those differences when we do our direct
comparison between 2021 and 2022 at the sites of interest to the LTNs.