Evaluation of Sample Taxicab Security Cameras

Background: Taxicab drivers have high homicide rates compared to all worker occupations. To help taxi fleets select effective taxicab security cameras, this project tested eight sample taxicab security cameras for determining their photographic quality which correlated to the effectiveness of in-taxicab facial identification. Methods: Five photographic quality metric thresholds: 1) resolution, 2) highlight dynamic range, 3) shadow dynamic range, 4) lens distortion, and 5) shutter speed, were employed to evaluate the photographic quality of the sample cameras. Waterproof tests and fire-resistive tests on recording memory cards were conducted to determine the memory card survivability in water and simulated fire. Results: The Full-HD (1920 × 1080 pixels), HD (1280 × 720 pixels) and dual-lens VGA (2 × 640 × 480 pixels with wide-angle and telephoto lenses) cameras performed well in resolution tests in daylight conditions. The resolution of a single-lens VGA (640 × 480 pixels) camera did not meet the resolution minimum requirements. All of the recording memory cards passed the five-meter/72-hour waterproof test. A fire resistant chamber made with one fire insulation material could protect a single memory card at 538 ̊C/1000 ̊F for a five-minute simulated fire test. Conclusions: Single-lens VGA-resolution (640 × 480 pixels) cameras are not suggested for use as security cameras in taxicabs with two or more rows of seats. The recording memory cards can survive 5-meter/72-hour waterproof tests. The memory card chamber built with an existing heat insulation material can protect an individual memory card during 538 ̊C (1000 ̊F)/5-minute fire resistance oven-test.


Introduction
Workplace violence has consistently been a leading cause of workplace fatalities and injuries since national occupational health surveillance efforts began at the National Institute for Occupational Safety and Health (NIOSH) in 1980 [1].The latest data available from the Bureau of Labor Statistics reveals that in 2014 there were 409 workplace homicides, making workplace homicides the fourth leading cause of work-related fatalities [2].There were 31 homicide fatalities in the Taxi and Limousine Sector in 2014 [2].Taxicab drivers, within the transportation industry, have the highest homicide rates among all industries (10 per 100,000 workers in 2014), 35 times greater than that among all workers (0.28 per 100,000 workers in 2014) [3].
To improve taxicab driver safety, many cities have installed equipment to help reduce crimes against taxicab drivers, including taxicab partitions and taxicab security cameras.In recent years, the latter intervention-security cameras-have become a popular alternative.Some cities have already installed security cameras in their taxicabs as a deterrent for crimes against taxicab drivers [4].NIOSH has completed epidemiologic studies that suggest taxicab security camera systems are highly effective in reducing taxicab driver fatalities [4].The studies showed that the cities with taxicab cameras experienced a threefold reduction in taxicab driver homicides compared with control cities.However, there is no peer-reviewed published literature to evaluate the technical effectiveness of current taxicab security camera models in use in the U.S. for taxicab customer facial identifications.Also, there is no national taxicab camera selection guidance in the US.Only a few domestic and international cities have issued local taxicab camera regulations or guidance [5]- [11], or study reports on taxicab crime reduction after taxicab security camera installation [12] [13].
A NIOSH research engineering project, entitled "Taxicab Security Camera System Evaluation Study", was developed in response to a request by the International Association of Transportation Regulators (IATR).The project conducted a series of camera tests in various in-taxicab light and seat conditions to (1) determine the minimum technical requirements for an effective security camera system in taxicab facial identification in Phase I of the project and (2) evaluate market-available sample taxicab security cameras with the minimum technical requirements as the metric thresholds for Phase II of the project.Phase I developed five photographic minimum quality metrics for evaluating in-taxicab performance of a taxicab security camera: 1) photograph resolution, 2) highlight dynamic range, 3) shadow dynamic range, 4) lens distortion and 5) shutter speed [14].An in-cab facial photograph taken by a security camera, with the quality at or above the metric thresholds, may contain sufficient facial information to allow customer identification, if necessary.In order to help transportation regulators and taxi fleets select effective taxicab security camera systems, Phase II evaluated eight sample taxicab security cameras (either market-available or pre-market) to determine how the photographic quality of the sample cameras correlated to the effectiveness of in-cab customer facial identifi-

Overview of Taxicab Security Camera Evaluation
Minimum Requirements for Taxicab Security Cameras.To comprehensively assess a taxicab security camera's photographic ability, the study in Phase I determined the thresholds of five minimum photographic quality requirements.These requirements were used as the technical quality metrics to evaluate the photographic quality of a taxicab security camera which correlates to the effectiveness of in-cab facial identification [14].The study quantified the thresholds of these five metrics under four extreme taxicab light conditions and in three cab-seat positions.These thresholds, which were developed in Phase I, are shown in Table 1.More details regarding the methods and results of Phase I of the project are available in Zeng et al. [14].The dynamic range and lens distortion thresholds in the table were re-measured by photographic quality test software Imatest Master (Imatest LLC, Boulder, CO), so that these thresholds would be compatible with the sample camera test results which were also measured by Imatest Master.
Camera Resolution.The camera resolution was measured by "line-widths per head height (LPHH)" in this study to normalize the captured facial image resolution of a customer sitting in either a front seat or back seat.When the camera resolution was measured in Project Phase I study, the head height was defined as 30 cm, in order to include different human subject head heights in the photographic test charts (22.0 -26.4 cm).In order to simulate a generalized human head in the camera tests, the head height of a 99 th percentile male (25.5 cm) in Phase II was defined as the head height in camera resolution measurements [15].
Subsequently, each of the 18 resolution thresholds in Camera Shutter Speed.Due to equipment setup difficulties in the rear-right and front-right seats, the shutter speed thresholds were not measured in these seats.Table 1 shows the shutter speed thresholds only in rear-middle seat.The median shutter speed threshold is 33.3 ms.

Experimental Setup for Sample Camera Evaluation
The taxicab security camera evaluation was conducted in a simulated taxicab with artificial lighting gear which simulated four extreme light conditions L1, L2, L3 and L4, as shown in Figure 1 and Figure 2.During evaluation tests, each of the eight sample cameras was mounted on a tripod standing in front of the central console near the rear-view mirror.The camera under test, which was aimed to the rear-middle seat, photographed two specially designed test charts for measuring the minimum photographic requirement metrics.A rectangular test chart, which measured camera resolution, dynamic range and lens distortion, was mounted on the head rest of each of the mentioned three seats, one at a time.A circular rotating test chart, which measured the camera shutter speed, was mounted in the rear-left (driver's side) seat.
Rectangular Test Chart.The rectangular test chart was photographed during sample camera evaluations for determining camera resolution, dynamic range and lens distortion, as shown in Figure 3.There was a slanted square on the right-hand side of the chart for measuring camera resolution by using the "Rescharts" module of Imatest Master.Camera resolution was determined by measuring the modulation transfer function (MTF) of the slanted square image using Imatest Master [18].In post-test data analyses, the software measures the MTF of the slanted edge in the captured images.The photographic resolution of a camera is defined as the spatial frequency as the measured MTF falls to 50% from its peak.The unit of the camera resolution in Imatest Master is line-widths per picture height.(LPHH, Head height = 25.5 cm).
The 20-step Q-14 gray scale was on the top of the rectangular chart for the camera dynamic range measurement.The camera dynamic range was measured by using the "Stepchart" module of Imatest Master [19].On the left-hand side of the chart there was a rectangle stripe for measuring the lens distortion using the "Distortion" module of Imatest Master [20].Lens distortion is an optical aberration that causes straight lines to curve near the center or edges of an image.The distortion is worse in front-seat facial images than in rear-seat images, therefore, only the front-seat lens distortion was measured in post-test data analyses.At 1/80 S, squares in Block 1 were separate.

Eight Sample Cameras under Test
A total of eight sample taxicab security cameras C1 ~ C8, were evaluated in the simulated taxicab.Among the eight cameras, camera C1 had a full high definition (FHD) image sensor (1920 × 1080 pixels).Camera C2 was a premarket camera with dual lenses and dual image sensors (2 × 720 × 572 pixels).The camera had dual lenses with one wide-angle lens focused to the front-seat customer/driver, and one telephoto lens focused to the rear-seat customers.The camera was only available to the project for a limited time, and was only partially tested.Camera C3 was also a dual-lens and dual-image sensor (2 × 720 × 572 pixels) camera with the left-lens focused to the left side of the cab and the right-lens focused to the right-side.Cameras C4, C5, C6 and C8 were common taxicab security cameras which had a single VGA (640 × 480 pixels) image sensor.Camera C7 had a high definition (HD) image sensor (1280 × 720 pixels).Each of the sample cameras captured at least five image frames in each combination of the four light conditions (L1 ~ L4) and three seat positions (rear-middle, rear-right and front-right).
The three best images from the five captured frames were selected to perform post-test data analyses using the software Imatest Master.

Sample Camera Evaluation Procedures
Capture Test Chart Images.One at a time, each of eight sample cameras, mounted near the rear-view mirror of the simulated taxicab, captured the images from the rectangular and rotating test charts which were placed in the cab-seats, as shown in Figure 6.The rectangular chart was mounted near the head rest of the front-right, rear-right and rear-middle seats, one seat at a time.The rotating chart was mounted on a specially designed chart stand in the rear-left seat, rotating at the rim speed of 245.2 cm/second.The test charts were illuminated by seven white Light Emitting Diode (LED) panels and four incandescent light bulbs to simulate four extreme light conditions (Figure 1).subtracting the number of recognizable gray steps from 10.In shadow dynamic range measurement, the "Stepchart" module selected gray steps 1 to 20 as the ROI to determine the number of recognizable gray steps.Figure 8  During lens distortion measurement the "Distortion" module of Imatest Master selected the vertical edge of the rectangle stripe in the rectangular test chart as the ROI and measured the distortion coefficient of the image in percentage.Figure 10 shows the test resulting distortion charts with different distortion coefficients.
Shutter Speed.The shutter speed of a camera under test was determined by examining the pattern of blurred square traces in the rotating test chart in the captured cab images (Figure 4 and Figure 5).The trace examination was started from 1/50 second block (Block 1) of the chart, and continued until the 1/15 second block (Block 6).If the square traces merged in a block, the camera shutter speed was equal or slower than the shutter speed that the block indicated.If the square traces were not merged in the block, the shutter speed was faster than the shutter speed of the block.Figure 11 shows the rotating chart patterns with three different camera shutter speeds.

Recording Media Waterproof Test Procedures
The recorded data stored on a flash memory card should not be damaged as the    The pipe was filled with five meters of tap-water.The flash memory cards were submerged in the water for 72 hours, as shown in Figure 12.Then, the memory cards were air dried at room temperature for 48 hours.Each of the dried memory cards was inserted into a PC, and the video clips stored on the cards were played by a PC to examine the integrity of the cards.

Recording Media Fire Resistance Test Procedures
To protect the recorded video data during a taxicab fire, the data storage media should be fire resistant.At the time this study was performed, there was no specific standard to regulate the fire resistance of taxicab recording media.Currently, there is no U.S. standard for taxicab fire resistance requirement.The "ASTM E119-15: Standard Test Methods for Fire Tests of Building Construction and Materials" [21] and "UL 72.Standard for Tests for Fire Resistance of Record Protection Equipment" [22] were used to define taxicab fire resistance requirement specifications.The purpose of this requirement was to ensure that the recording media of taxicab security cameras can be deemed as being able to provide "Resistance to Vehicle Fire".This specification was based on the lowest temperature tests defined in ASTM E119-15 and UL 72.The recording media may be considered as fire resistant to 538˚C (1000˚F) as per ASTM E119-15 methodology or equivalent certification [21].The Basic Fire Test comprised the following steps: 1) A furnace is heated to 538˚C (1000˚F).
2) The memory card in a fire resistant chamber is placed in the furnace.
3) After five minutes at 538˚C (1000˚F) the furnace is switched off.
4) The chamber is immediately removed from the furnace.
Once the chamber containing the memory card is removed from the furnace and allowed to cool to room temperature, the information on the memory card prior to it being placed in the furnace must be recovered.
Since there were no commercially available fire resistant chambers for taxicab security cameras, several fire resistant chambers were constructed for fire resistance tests conducted in this study.Based on the ASTM E119-15 temperature profiles in the fire resistance test, two materials were selected to construct the fire resistant chamber for ease of purchase, convenience, temperature rating, and performance.The materials, which were evaluated in the fire resistance tests, were thermal insulation material (TIM) No. 1  0.1915 0.1 -0.22A simplified analysis was performed using ANSYS Workbench 12.01 software (ANSYS, Inc., Canonsburg, PA) to estimate chamber thicknesses that might be used in the fire resistance test.The thickness of the fire resistance chamber was 25.4 mm (1.0").In the tests, an SD flash memory card or flash card reader was placed in the chamber.Omega (Stamford, CT) XC-24-K-18 high temperature Nextel insulated thermocouples were inserted in the chamber and placed in the oven to measure chamber and oven temperature.A Model BF51732C Lindberg/Blue Thermo Scientific Furnace (Thermo Fisher Scientific, Inc., Waltham, MA) was used to generate the simulated fire temperature of 538˚C (1000˚F) for five minutes.The experimental setup for the fire resistance testing is shown in Figure 13.

Results of Post-Test Data Analyses
The results of post-test data analyses are listed in Tables 2-7.For comparison, the metric thresholds in Table 1 were also listed in Tables 2-6.The measured data in five quality metrics (camera resolution, highlight dynamic range, shadow dynamic range, lens distortion, and shutter speed) with eight cameras were compared with the metric thresholds in Tables 2-6, respectively.The metric data which were worse than the thresholds are referred as "bad" data; and the metric data which were better than or equal to the thresholds are referred as "good" data.A summary of infrared radiation source activations in L3 condition is shown in Table 7.A summary of the camera performance for each metric and the ranking are listed in Table 8.The effectiveness of a camera was determined by the number of "good" metric data.A camera would rank higher in a metric with more "good" data, and vice versa.As two cameras had the same number of "good" data, the one with better median performance value in that metric would have a higher rank.The median performance value is the median of all of the performance data of a camera in one metric and in all light and seat conditions.A summary of the metric performances with each camera and the total performance ranking are listed in Table 9.The metric performance of the cameras with the maximum, median and minimum values are shown in Table 10.

Camera Ranks
Camera C1 with an FHD image sensor had the highest photographic resolution rank.Camera C3 with two separate lenses, one focused on the left-hand side of the cab and another focused on the right-hand side, had the highest rank in both  Total Rank: a camera would rank higher with more data which were better than or equal to their thresholds.the highlight and shadow dynamic range metrics.Camera C1 also had the highest rank in lens distortion.Cameras C5 and C6, both with a single VGA image sensor, had the highest rank in shutter speed metric.In total performance ranking, the more the camera data were better than or equal to the thresholds, the higher the overall camera performance rank (Table 9).Camera C1 had the highest total performance rank.

Waterproof Test
After six flash memory cards, three in Compact Flash (CF) form factor and three in Secure Digital (SD) form factor, were submerged on the bottom of a fresh water pipe at 5 meters in depth for 72 hours, and dried in the air for 48 hours, the video clips stored on all of six cards were able to be recovered.

Fire Resistance Test
The results from the oven tests are shown in Figure 14.There were six oven test curves (inside-chamber temperature versus time) in the figure.In one oven test (temperature curve in purple), the memory media storage chamber was constructed using TIM No. 1.In the other five oven tests, the insulation material used to construct the chamber was TIM No. 2. The fire resistance test method requires that the recording media (flash memory card in these tests) should still be functional after the media, stored inside the chamber, is placed in an oven at 538˚C (1000˚F) for five minutes.A typical industrial grade memory card cannot be functional if the ambient temperature of the card exceeds 85˚C (185˚F) [23].*Head Height = 25.5 cm (Head Height of a 99th Percentile Male).

Conclusion
The camera tests suggest that single-lens VGA-resolution (640 × 480 pixels)

Impact to Industry
This research should open discussion among safety professionals and design engineers for consideration of appropriate advanced camera techniques for the application in reducing taxicab driver homicide rates.

Figure 1 .
Figure 1.Reconstruction of light conditions in a simulated taxicab with seven white light emitting diode panels and four incandescent light bulbs.

Figure 2 .Figure 3 .
Figure 2. The simulated taxicab with white LED light panels and incandescent light bulbs.

Figure 4 .
Figure 4.The rotating test chart rotates with the rim speed of 245.2 cm/S.There are seven shutter speed identification blocks: Blocks 1 ~ 6 and Signal Block with three pairs of squares in each block.As the shutter speed decreases from 1/50 to 1/15 second, the squares become blurred and merge in Blocks 1 to 6 sequentially.

Figure 5 .
Figure 5.The rotating test chart on the left of the first row was still.The rest of nine charts rotated with the rim speed of 245.2 cm/S.The camera took nine photographs with nine different shutter speeds from 1/80 to 1/10 second.The blurred squares in Blocks 1 ~ 6 merged sequentially as the shutter speed decreased.

Figure 6 .
Figure 6.The sample camera test equipment setup.The rotating test chart was mounted in the rear-left seat.The rectangular test chart was mounted on rear-middle, rear-right and front-right seat, one at a time, while the camera under test captured cab images in each of these seat positions, and in four light conditions.
shows the dynamic range testing charts which determined the highlight dynamic range of the images.To compare different highlight dynamic ranges of post-test images, three Kodak Q-14 gray scale images, captured by three cameras with different dynamic ranges, and the dynamic range result charts measured by "Stepchart" module, are shown.The number of gray steps detected is shown on the upper chart of each dynamic range result chart.The number of washed out and merged gray steps is calculated by subtracting the number of detected gray steps from 10.The calculated washed out and merged gray steps are: (a) 8.2 (most merged gray steps, worse than any highlight dynamic range threshold, unacceptable), (b) 3.3 (on the highlight dynamic range threshold (black and white) in dark with backlight condition in the rear-middle seat) and (c) 0.23 (no merged gray steps, better than any highlight dynamic range threshold).Figure9shows the dynamic range testing charts which determined the shadow dynamic range of the images.To compare different shadow dynamic ranges of post-test images, three Kodak Q-14 gray scale images, captured by three cameras with different dynamic ranges, and the dynamic range result charts measured by "Stepchart" module, are shown.The number of gray steps detected, shown on the upper chart of each dynamic range result chart, is the number of recognizable gray steps.The shadow dynamic range of three post-test Kodak Q-14 gray scale images are: (a) 18.5 (most recognizable gray steps, better than any shadow dynamic range threshold); (b) 16.6 (close to the shadow dynamic range threshold (black and white) in dark condition and in rear-middle seat) and (c) 7.8 (least recognizable gray steps, worse than any shadow dynamic range threshold, unacceptable).

Figure 10 .
Figure 10.To compare different lens distortions of post-test images, three distorted test chart images, captured by three cameras with different lens distortions, and measured by "Distortion" module, are shown.The SMIA TV Distortion percentage on each chart is the lens distortion percentage of each test chart image.The minus sign before the number means barrel distortion.Three lens distortions are: (a) 32.5% (worse than the lens distortion threshold, unacceptable); (b) 23.5% (close to the lens distortion threshold) and (c) 7.5% (least distorted, below the lens distortion threshold).

Figure 11 .
Figure 11.The images of the rotating shutter speed test charts are shown with three shutter speeds: (a) 40 ms slowest shutter, unacceptable); (b) 25 ms (close to mean shutter speed) and (c) <16.7 ms (fastest shutter speed, much better than any shutter speed threshold).Signal Block is not shown in the charts.

Figure 12 .
Figure 12.The experimental setup for flash memory card waterproof tests.The memory cards were submerged in the tap-water pipe at the depth of five meters for 72 hours.

Figure 13 .
Figure 13.(Clockwise from top-left) (a) The overall experimental setup with data acquisition, thermocouples, and Thermo Scientific Furnace with proportional-integral-derivative control; (b) Piece of TIM No. 2 insulation which formed the cover of the insulation-box; (c) A TIM No. 1 multi-layer box to hold card; (d) Work-table for cutting and adhesive operations using insulation-refractory type paste to fix pieces together.
Only two sets of data were measured before Camera C2 was withdrawn during sample camera tests.*C5, *C6: The images captured by C5 and C6 were shown in only one quadrant of the image viewer screen.The infrared radiation sources of seven cameras (except C2, which was not tested in L3 condition) tested were not activated in L3 (dark with backlight) light conditions in the rear-right seat position, and five cameras (C4 ~ C8) did not activate their infrared radiation sources in L3 and in the front-right seat position.

Figure 14 shows
Figure14shows that the chamber temperature in all six tests did not exceed 85˚C in the first five minutes after the chambers were placed into the oven at 538˚C (1000˚F).During the cool-down time after the chambers were taken out of the oven, the chamber temperature with TIM No. 1 (the temperature curve in purple) raised to a maximum temperature of 138.2˚C (280.7˚F),exceeding the flash memory card maximum storage temperature of 85˚C (185˚F).Other chamber temperatures with TIM No. 2 were kept below 85˚C (185˚F) during the cool-down time with the maximum temperature of 72˚C (161.6˚F).
cameras are not appropriate for use as security cameras in taxicabs with two or more rows of seats.To meet resolution requirements in both the visible and infrared conditions, camera manufacturers might either redesign the camera lens to reduce lens chromatic aberration, or adjust the lens focus to a focal point in the middle of visible light focus and infrared radiation focus.Most of the cameras with the light sensor facing rearward falsely deactivated their infrared radiation sources with backlight illumination.Most of the cameras met or exceeded the minimum requirements for lens distortion and shutter speed.The recording memory cards passed the 5-meter/72-hour waterproof tests.The memory card chamber built with one heat insulation material was able to protect an individual memory card during 538˚C (1000˚F)/5-minute fire resistance oven-test procedure.This camera test protocol could be used by taxi fleets, transportation regulators and/or taxicab security camera manufacturers to ensure that the camera system performance meets the minimum quality requirements for effective in-cab facial identifications.The above camera tests were conducted in a simulated two-row seating taxi-cab.These test results could not be applied to three-row seating taxicabs due to the extended distance from the camera to the third-row seat customers.Since more three-row seating taxicabs are used in taxi industry, additional camera tests are suggested in a simulated three-row seating taxicab.

Table 1
[17]right light condition.Camera dynamic range in shadow (DRS) measures the ability of a taxicab camera to detect shadow details in a captured image in twilight light conditions[16][17].The dynamic range can be observed on a standard Kodak Q-14 gray scale with 20 gray step patches (Eastman Kodak Company, Rochester, NY) in the captured taxicab test image.The light density difference between two adjacent gray steps is 1/3 Exposure Value (EV).

Table 1 .
Summary of metric thresholds in four lights and three cab seats.Unable to measure the shadow dynamic range thresholds by Imatest software due to vulnerable image light conditions.Substituted with the median of 8 measureable shadow dynamic range thresholds.**Resolutionthresholdswerenormalized with the height of a 99th percentile human head (25.5 cm).Dynamic range thresholds and lens distortion thresholds were re-measured by Imatest software.Since the images captured in the front seats have more severe lens distortion than that in rear seats, it is unnecessary to measure lens distortion in rear seats.Only the front seat lens distortion thresholds are shown in Table1.The lens distortion median threshold is 24.4%. *
*A: Only two sets of data were measured before Camera C2 was withdrawn during sample camera tests.*B: Excessively overexposed.Data could not be measured.*C: IR-LED radiation source was not activated.Data could not be measured in dark conditions.*C5, *C6: The images captured by C5 and C6 were shown in only one quadrant of the image viewer screen.

Table 3 .
Sample camera test results: highlight dynamic range.Unit: merged gray steps.A: Only two sets of data were measured before Camera C2 was withdrawn during sample camera tests.*B: The lens view angle was too narrow to cover whole gray scale.Reliable measurement was not possible.*C: Excessively overexposed.Data could not be measured.*D: Very low resolution, pseudo color, and noisy.Data could not be measured.*E: Low resolution and noisy.Data measurement was not reliable.*C5, *C6: The images captured by C5 and C6 were shown in only one quadrant of the image viewer screen. *

Table 4 .
Sample camera test results: shadow dynamic range.Unit: recognizable gray steps.

Table 5 .
Sample camera test results: lens distortion.Unit: %.Only two sets of data were measured before Camera C2 was withdrawn during sample camera tests.*B: IR-LED light source was not activated.Data could not be measured in dark conditions.*C: Due to the narrow IR-LED radiation angle, the light condition was too dark, and the lens distortion could not be measured.*D: The test chart image was washed out due to overexposure.**: The distortion value is higher than those measured in L2 and L3 light conditions.This phenomenon was caused by the camera's over-sharpening effect in L1 and L4 conditions, which was not related to lens distortion.*C5, *C6: The images captured by C5 and C6 were shown in only one quadrant of the image viewer screen. *A:

Table 7 .
Sample camera test results: infrared radiation source activation.

Table 8 .
Camera performance ranks of quality metrics.

Table 9 .
Metric performance ranks for each camera.

Table 10 .
Camera performance in five metrics (maximum, median and minimum).

Table 16 .
Suggested consolidated metric thresholds (median of total thresholds).