Device Installation

The device installation includes the tube installation and the automatic counter set up. The installation is discussed in sections 3.6.4.1 and 3.6.4.2

84 3.6.4.1 Tube installation

Two sets of pneumatic tubes each were laid for traffic data collection at the entry and circulating roadway. The first pneumatic tube was laid perpendicular to traffic flow rate; this was achieved by making sure that the tube was laid perpendicular to the side kerb of the entry and circulating roadway. End plugs were fixed on the end of the tubes and they were further tightly tied in two knots to avoid the leakage of air pulse emissions from the tube, which could give an error in the traffic data collected by the roadside unit. The end of the tube was tightened with a flap and nailed with a road nail into the road pavement surface, at the two edges of the road, with the use of heavy duty hammer. The tube was stretched at about 10 to 15% of the road width covered, to minimise lateral movement as recommended by the ATC provider. The 1m calibrated wooden rod was placed at the two ends and at the middle of the tubes to separate the tubes at the 1m interval to achieve parallel tubes. After tensioning, the tube was tested by pulling the tube from the road’s surface, the tubes pulled back the hand which showed that it was properly tensioned. The 1m interval was checked after tensioning to make sure that the tension did not shift the position of the tubes. The length of the tubes was checked to make sure they were the same length, to avoid errors in speed accuracy and wheelbase results.

Centerline flips were fixed with road nails at two more points each on the tube to further secure the tubes lateraly. These points were at the center of each lane of the double lanes, at the entry and circulating roadway, to avoid the flap being in vehicle tire path. Heavy duty bitumen tape was cut at about 200mm by 200mm and fixed on the tube at the interval to further secure tubes against lateral movement. The tubes were connected to the automatic counter device. The first tube to be hit by a vehicle was connected to terminal A of the device while the second tube was connected to the terminal B of the device. The devices were set at the selected roundabout, one at the entry and the other at circulating roadway. The typical sensor configuration is shown in Figure 3.14. There is a little warning that the use of one logger on multi-lane uni-directional may result in an error in the traffic data collection. This may not be so, it can be argued that the first vehicle in the first lane will send the air pulse to the sensor before the vehicle in the second lane due to the air pulse distance travel. The air pressure at the first lane will be stronger and travel faster than the air pressure from a vehicle in the second lane. The speed at the entry and circulating roadways are low, if the vehicle hit the tube simultaneously, the traffic data will be very good. Though, it can

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be argued as well that frequent occurrence of simultaneous hits on the pneumatic tubes can reduce the data quality. This can be checked by assessing the single unit convenience for the data, acceptable for the survey site.

Figure 3.14: Typical sensor configuration

The air sensor device was placed in plastic and, further, in a wooden box and tied to a permanent structure like a signpost or a street light pole. The device was further configured with a laptop to record data as shown in Figure 3.15.

86 3.6.4.2 Automatic Traffic counter setup

It is very important to know the status of the ATC before setting up the device for traffic data collection. The status of the battery was checked. Firstly, the continuous blinking light which comes up at every 8 seconds, when the device is in an idle state, shows that the battery is active. The tubes were connected to the air sensor device in the automatic counter. Care was taken to connect the first tube to be hit by a vehicle to the terminal A and the second to terminal B of the sensor device. After the two tubes had been plugged into the terminals, the USB communication cable was used to connect the air sensor device to the laptop. The setup software was activated and the status icon was opened. In the status box, the level of energy and the lifetime of the energy in the battery were checked. The battery status was checked to avoid a shortage in power supply to the device during data collection. The second most important checking carried out was the memory status of the device in order avoid memory shortage during the traffic survey, which might lead to the device cutting off during data collection. The next step was the activation of the setup icon and filling in the site description, which included the site name, the site number, and the direction of traffic flow rate as the vehicle hits the tube as ‘ÁB’. The spacing between the tube, the data collection starting time, and sensor configuration were inputted into the setup dialog box. The setup dialog box is shown in Figure 3.16.

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Data collection started during the fixed time after the setup box was closed. The measure taken to make sure the device was functional was checking the display of vehicles that hit the tube on the laptop by the selection of the view icon on the setup software. Whenever a vehicle hits the tube, rolling time mode will be displayed on the laptop screen. The device was set to start counting immediately from the date of setup but the data for the first two days was not used in the study to allow drivers on the roundabout to get familiar with the installed tubes, on both the entry and circulating roadway to aviod driver reactions to the tubes. Individual vehicle data was recorded in the air sensor memory unit. The memory status was continually checked at intervals of five days to avoid full usage of the memory, which might make the device stop data collection until unloading the data.