BL CLASS 3 SENSORSFOR BICYCLE COUNTINGBL Class 3 Sensors for Bicycle Counting

TE Connectiviy’s (TE) RoadTrax BL piezoelectric axle sensors are available in Class 3
forms, specifically intended for bicycle detection (counting, direction and speed) inpermanent installations. Class 3 sensors are available in lengths from 1.0 m to suit narrowpaths/lanes and with shorter feeder length (10 m). Our optional split-sensor designs
allow two riders traveling abreast at just 0.75 m spacing to be detected separately.
When mounted in lanes used for mixed traffic, Class 3 sensors can still be used to detect
the full range of motor vehicle axles.

Introduction
Many countries are encouraging the general public to use
bicycles more regularly as a means of transportation, partly
as a way to reduce passenger car usage and also to improvegeneral health and fitness. This can involve setting up
dedicated cycle lanes in urban areas and cycle paths acrossrural landscapes.
Provision of this infrastructure necessarily bear some cost,both in terms of installation and subsequent maintenance,
therefore the responsible agencies have increasing interest inmonitoring uptake by means of bicycle counting.
There are some key differences between existing roadtraffic (vehicular) counting/classification methods and therequirements for bicycle counting:• Detection using inductive loops or magnetometers isdifficult, as the area of coverage is not uniform across thefull lane width• Short-range radar detectors may not function well in rain
• Two or more bicycle riders may travel abreast, making
transverse-firing optical or passive infra-red (PIR) detection
potentially inaccurate• Cycle lanes tend to be very narrow• Above-ground detectors (pneumatic tubes, PIR) may beprone to vandalism at rural sites that are concealed fromview
• In urban environments, some lanes may alternate between
bicycle and vehicular traffic usage at different times of day

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The RoadTrax BL piezoelectric axle sensor is well-suited toaddress these requirements. The BL has a long history of
deployment for use in concrete and asphalt pavements, forthe purposes of axle counting, vehicle classification, speed
measurement and enforcement and high-speed weigh-inmotion. Motorcycles and mopeds already require detection
as part of existing motor vehicle classification schemes.
Bicycle wheel detection uses the same principle as otherheavier axles: a tire passing over the installed sensor willproduce a charge pulse in response, with the amplitude
proportional to tire pressure (and therefore axle load), andpulse width proportional to tire footprint length.
Although the load exerted by a bicycle tire is necessarily much
lower than typical of motorized vehicles, the piezopolymer
sensor at the core of the BL has very high dynamic range, andsignals from bicycle crossings should be distinct and clear.

PAGE 2

BL Class 3 Sensors for Bicycle Counting

BL Class 3 Sensors
To address the specific requirements for bicycle detection TE
expanded the existing BL product range of Class 1 and Class 2
sensors.
Class 3 sensors are identical in construction, and differ only inthe following ways:

Use of the RoadTrax BL sensor for bicycle detection offers thefollowing advantages:• Permanent buried installation, flush with pavement surface– robust and imperceptible to cyclists• No poles or gantries required• Class 3 sensors are not passed through our uniformity test
after production. We expect these sensors generally toshow similar distribution of sensitivity and uniformity as ourClass 2 sensors (uniformity < ± 20 % along length)• Speed and direction easy to resolve, with short pulse signals
from two transverse sensors• Available standard sensor lengths range from 1.0 m
to max 5.5 m• Unaffected by rain and other adverse weather conditions• Class 3 sensors are offered with 10 m or 35 m feeder
cables. On cycle paths, it is common to have the detection
electronics relatively close to the measurement site
• An additional split-sensor configuration has beendeveloped, which offers two separate sensing regions within
a single brass length, with very small gap between theactive sensors. Each end of the sensor is then terminated tofeeder cable, giving a “double-ended” sensor• Simple electronic signal processing required• Very low power requirement (self-generated signals),suitable for battery/solar-powered systems• Short sensors available to cater for narrow lanes• Unique split-sensor designs available for improved lane
coverage and counting accuracy

The recommended installation procedure is also identical forasphalt or concrete pavements.

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BL Class 3 Sensors for Bicycle Counting

Typical Output Signals

Typical output – single sensor
0,5

0,4

0,3

Charge output (nC)

Figure 1 shows the charge signal
produced from a Class 3 sensor installed
full-lane-width in asphalt road open to
all traffic. Sensor capacitance (including
feeder cable): 5.86 nF, giving opencircuit voltage peaks of 34 mV (frontaxle) and 65 mV (rear axle). Speed
11.8 km/h. Total weight approx 100 kg.
Wheelbase 0.92 m. Air temperature+8 °C.

0,2

0,1

0

-0,1

-0,2

-0,2

-0,1

0

0,1

0,2

0,3

0,4

0,5

0,6

Time (s)FIGURE 1

Figure 2 displays the same bicycle andrider passing over two similar sensors,
spaced 0.35 m apart. Speed anddirection are deduced from the time
separation between the two waveforms.
Wheelbase length can be calculated
from time separation between front
and rear axles, if speed is known. Tire
footprint length can be estimated frompulse width if speed is known.

Typical output, two sensors at 0.35 m spacing

Note that bicycle tire footprint length
will be significantly shorter than typical
car tire (or truck) footprint, as illustrated
in figure 3.

0,4

1

0,2

0,8

0

0,6

-0,2

0,4

-0,4

0,2

-0,6

0

-0,8

-0,2

-0,1

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

-0,2

FIGURE 2

Footprint length comparison

Bicycle FPL (50mm) compared with 4x4 (128 mm), normalised amplitudes
1,25

1

0 ,75

Relative amplitude)

Figure 3 is derived from two raw
waveforms produced by the same
sensor, normalized to same peak
amplitude. The blue curve is the front
axle of a bicycle. The orange curve isfront axle of a 4x4 (SUV). The X-axis
has been scaled into units of distance,
knowing the speed of each axle crossing.
50 % of peak amplitude points were used
to estimate the footprint length (50 mm
for bicycle, 128 mm for 4x4).

0 ,5

0 ,25

0

-0,25

-0,2

-0,15

-0,1

-0,05

0

0,05

0 ,1

0 ,15

0 ,2

Distance (m)FIGURE 3

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PAGE 4

BL Class 3 Sensors for Bicycle Counting

Discussion of Output Amplitudes
Although the sensitivity of a BL sensor to compressive force istypically in the range 40-60 pC/N, the apparent sensitivity ofa sensor installed in the pavement at normal depth and using
typical resin will be much lower, because much of the force
exerted by the tire will bypass the sensor itself.

We expect the apparent sensitivity to be below 1 pC/N,and likely around 0.75 pC/N for an installed sensor. A tableshowing approximate peak charge and voltage output levels
for various axle loads is shown below:

kg

axles

kg/axleN/axlenC pk

Voc//10n

STGO Cat 3 limit

16500

1

16500

161865121

12.1

HGV (max driven)

11500

1

11500

11281585

8.5

HGV (typ)

6000

1

6000

58860

44

4.4

Van

3000

2

1500

14715

11

1.1

Car (large)

2500

2

1250

12263

9.2

0.92

Car (small)

1200

2

600

5886

4.4

0.44

Motorcycle

300

2

150

1472

1.1

0.11

Bicycle (typ)

100

2

50

491

0.37

0.04

Bicycle (light, child)

40

2

20

196

0.15

0.01

From this table, we predict 0.37 nC peak for each axle of abicycle/rider with total weight 100 kg. In the measurement
data, we saw peaks of 0.2 nC (front) and 0.38 nC (rear), a little
lower in total than the expected value but correct in orderof magnitude. The absolute output level of a BL sensor is afunction of installed depth and of temperature. Waveform
data shown above were collected with air temperature around+8°C. At lower temperatures, the hardness of the installation
resin increases, and lower peak force is transferred to thesensor element.

Bicycle Counting Accuracy
The accuracy of any bicycle counting system in any specificinstallation depends not just on the sensor type andperformance, but also on the algorithms adopted by the
instrumentation, the configuration of the site, and the natureof local traffic.
As a producer of the sensor only, TE cannot lay claim toany specific accuracy level. With this said, one system using
our BL piezoelectric sensors has achieved accuracy up to
100% (no missed bicycles, no false positives where othervehicles or pedestrians were mis-classified as bicycles) in
given circumstances, and 99.0 % over a longer time interval(2 apparent missed events, with some question over thereference count accuracy).

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In a different multi-technology comparison trial, BL sensors
were found to offer overall detection accuracy (measured/actual count) of up to 96.3 % (7865/8171) with sensitivity
94.3 % and positive prediction value (PPV) 97.2 %.
A similar system from another manufacturer also using
BL sensors achieved a false positive rate of just 0.4 %(PPV 99.6%). The report concluded that systems deploying
BL sensors are suitable for off-road paths and separated
cycleways and acceptable for on-road monitoring in mixed
traffic.

PAGE 5BL Class 3 Sensors for Bicycle Counting

Available Part Numbers
Single-ended sensors

Sensor length in the part description below refers to "visible brass" length (L) as shown above
Part Number

Description

Part Number

Description

1-1007296-0

BL CL3 1.0M SENSOR/10M CABLE

20012270-00

BL CL3 1.0M SENSOR/35M CABLE

1-1007296-1

BL CL3 1.1M SENSOR/10M CABLE

20012270-01

BL CL3 1.1M SENSOR/35M CABLE

1-1007296-2

BL CL3 1.2M SENSOR/10M CABLE

20012270-02

BL CL3 1.2M SENSOR/35M CABLE

1-1007296-3

BL CL3 1.3M SENSOR/10M CABLE

20012270-03

BL CL3 1.3M SENSOR/35M CABLE

1-1007296-4

BL CL3 1.4M SENSOR/10M CABLE

20012270-04

BL CL3 1.4M SENSOR/35M CABLE

1-1007296-5

BL CL3 1.5M SENSOR/10M CABLE

20012270-05

BL CL3 1.5M SENSOR/35M CABLE

1-1007296-6

BL CL3 1.6M SENSOR/10M CABLE

20012270-06

BL CL3 1.6M SENSOR/35M CABLE

1-1007296-7

BL CL3 1.7M SENSOR/10M CABLE

20012270-07

BL CL3 1.7M SENSOR/35M CABLE

1-1007296-8

BL CL3 1.8M SENSOR/10M CABLE

20012270-08

BL CL3 1.8M SENSOR/35M CABLE

1-1007296-9

BL CL3 1.9M SENSOR/10M CABLE

20012270-09

BL CL3 1.9M SENSOR/35M CABLE

2-1007296-0

BL CL3 2.0M SENSOR/10M CABLE

20012270-10

BL CL3 2.0M SENSOR/35M CABLE

2-1007296-1

BL CL3 2.1M SENSOR/10M CABLE

20012270-11

BL CL3 2.1M SENSOR/35M CABLE

2-1007296-2

BL CL3 2.2M SENSOR/10M CABLE

20012270-12

BL CL3 2.2M SENSOR/35M CABLE

2-1007296-3

BL CL3 2.3M SENSOR/10M CABLE

20012270-13

BL CL3 2.3M SENSOR/35M CABLE

2-1007296-4

BL CL3 2.4M SENSOR/10M CABLE

20012270-14

BL CL3 2.4M SENSOR/35M CABLE

2-1007296-5

BL CL3 2.5M SENSOR/10M CABLE

20012270-15

BL CL3 2.5M SENSOR/35M CABLE

2-1007296-6

BL CL3 2.6M SENSOR/10M CABLE

20012270-16

BL CL3 2.6M SENSOR/35M CABLE

2-1007296-7

BL CL3 2.7M SENSOR/10M CABLE

20012270-17

BL CL3 2.7M SENSOR/35M CABLE

2-1007296-8

BL CL3 2.8M SENSOR/10M CABLE

20012270-18

BL CL3 2.8M SENSOR/35M CABLE

2-1007296-9

BL CL3 2.9M SENSOR/10M CABLE

20012270-19

BL CL3 2.9M SENSOR/35M CABLE

3-1007296-0

BL CL3 3.0M SENSOR/10M CABLE

20012270-20

BL CL3 3.0M SENSOR/35M CABLE

20012269-00

BL CL3 3.25M SENSOR/10M CABLE

20012270-21

BL CL3 3.25M SENSOR/35M CABLE

20012269-01

BL CL3 3.5M SENSOR/10M CABLE

20012270-22

BL CL3 3.5M SENSOR/35M CABLE

20012269-02

BL CL3 3.75M SENSOR/10M CABLE

20012270-23

BL CL3 3.75M SENSOR/35M CABLE

20012269-03

BL CL3 4.0M SENSOR/10M CABLE

20012270-24

BL CL3 4.0M SENSOR/35M CABLE

20012269-04

BL CL3 4.25M SENSOR/10M CABLE

20012270-25

BL CL3 4.25M SENSOR/35M CABLE

20012269-05

BL CL3 4.5M SENSOR/10M CABLE

20012270-26

BL CL3 4.5M SENSOR/35M CABLE

20012269-06

BL CL3 4.75M SENSOR/10M CABLE

20012270-27

BL CL3 4.75M SENSOR/35M CABLE

20012269-07

BL CL3 5.0M SENSOR/10M CABLE

20012270-28

BL CL3 5.0M SENSOR/35M CABLE

20012269-08

BL CL3 5.25M SENSOR/10M CABLE

20012270-29

BL CL3 5.25M SENSOR/35M CABLE

20012269-09

BL CL3 5.5M SENSOR/10M CABLE

20012270-30

BL CL3 5.5M SENSOR/35M CABLETE CONNECTIVITY SENSORS /// WHITE PAPER

PAGE 6BL Class 3 Sensors for Bicycle Counting

Available Part Numbers
Double-ended (split) sensors

Visible brass length L1 is split into two equal parts.
For example, part number 1007375-1 has length L1 of 1.50 m, described as 0.75M*2 in the table below.
Part Number

Description

1007375-1

CLS 3,0.75M*2 SEN/10M CABLE

1007375-3

CLS 3,0.75M*2 SEN/30M CABLE

1-1007375-1

CLS 3,1.0M*2 SEN/10M CABLE

1-1007375-3

CLS 3,1.0M*2 SEN/30M CABLE

2-1007375-1

CLS 3,1.25M*2 SEN/10M CABLE

2-1007375-3

CLS 3,1.25M*2 SEN/30M CABLE

3-1007375-1

CLS 3,1.5M*2 SEN/10M CABLE

3-1007375-3

CLS 3,1.5M*2 SEN/30M CABLE

4-1007375-1

CLS 3,1.75M*2 SEN/10M CABLE

4-1007375-3

CLS 3,1.75M*2 SEN/30M CABLE

4-1007375-5

BL CLS 3,1.75M*2 SEN/50M CABLETE CONNECTIVITY SENSORS /// WHITE PAPER

PAGE 7

ABOUT TE CONNECTIVITYTE Connectivity (TE) is a global technology leader, providing sensors and connectivity essential in
today’s increasingly connected world. We are one of the largest sensor companies in the world withsolutions that are vital to the next generation of data-driven technology. TE’s portfolio of intelligent,
efficient and high performing sensors are used for customers across several industries, from automotive,
industrial and commercial transportation and aerospace and defense, to medical solutions and consumer
applications.

AUTHOR
Richard Brown, Field Application Engineer, TE Connectivity

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