Measuring, Characterizing, and Reporting Pavement Roughness of Low-Speed and Urban Roads (2019)

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C-1 A P P E N D I X C Ride Experiment This appendix describes an experiment conducted to correlate objective measurements of ride quality to measures of road roughness on urban and low-speed roadways. The experiment included simultaneous measurements of longitudinal road profile and accelerations at interfaces between the driver and the host vehicle on 29 urban and low-speed pavement sections using 3 test vehicles. This appendix describes the test vehicles, instrumentation, test sections, and test procedures. C.1 Test Vehicles The measurements were conducted using three host vehicles: • 2003 Nissan Altima; data collected September 25–October 7, 2015 • 2013 Hyundai Tucson; data collected October 30–November 11, 2015 • 2008 GMC Savana; data collected December 3–December 10, 2015 The Altima and Savana were selected as examples of a mid-sized sedan and a full-sized van. Vehicles in these market segments represent potentially diverse ride response, because they differ from each other in geometry, mass distribution, and suspension characteristics. The specific vehicles were selected because they were in use in other studies. The Tucson was selected to represent a third market segment (SUVs) with ride characteristics different from both the van and sedan. The vehicles were inspected prior to instrumentation and, when necessary, worn components were replaced (for example, new shock absorbers were installed on the van). Table C-1 provides general information about each vehicle. Vehicle weights listed in the table below include the driver and operator, instrumentation, and a fuel tank between ¾ full and full. Figures C-1 through C-3 provide photos of the test vehicles. Table C-1. Vehicle descriptions. Vehicle 2003 Nissan Altima 2013 Hyundai Tucson 2008 GMC Savana VIN Number 1N4BL11E83C285779 KM8JTCAD5DU665937 1GTGG25C481234303 Tires P215/55R17 93H M+S P225/60R17 99H M+S T245/75R16E Cold Inflation Pressure (psi) 33 (front) 30 (rear) 33 (front) 33 (rear) 50 (front) 80 (rear) Wheelbase (in) 110.2 103.9 135.4 Track Width (in) 60.4 62.4 68.1 Total Weight (lb) 4,116 4,195 6,850 Front Axle Weight (lb) 2,132 2,018 3,460 Rear Axle Weight (lb) 1,984 2,178 3,390

C-2 Figure C-1. Instrumented Nissan Altima. Figure C-2. Instrumented Hyundai Tucson Figure C-3. Instrumented GMC Savana.

C-3 C.2 Instrumentation C.2.1 System Elements The instrumentation is comprised of four primary subsystems, with some additional sensors for diagnostic purposes. All of the equipment was integrated into a measurement platform, which could be moved between the different test vehicles with a minimum of effort. The instrumentation includes the following subsystems: • Data Acquisition System (DAS): The DAS enclosure, containing the central processing units (CPUs), interface boards, and signal conditioning, was mounted inside the trunk or rear cargo area of each vehicle. The power supply for the DAS, including a large backup battery, was mounted adjacent to it. This is shown in Figure C-4. Figure C-4. Power supply and DAS in Hyundai Tucson. • Vehicle Vibration Measurement: Vehicle ride response was measured using a suite of sensors at the driver-to-vehicle interfaces. Each vehicle was equipped with a servo-type accelerometer mounted to the floor at the driver’s feet and two instrumented seat pads with six degree-of-freedom inertial measurement units (IMUs). These are shown in Figures C-5 and C-6. To help characterize the road inputs to the vehicle, microelectromechanical (MEMS) accelerometers were mounted to the left and right steering knuckle of each vehicle to help characterize vehicle vibration response to road roughness. These accelerometers were aligned vertically with respect to gravity with the vehicle on a flat and level surface (see Figure C-7). • Inertial Profiler: The inertial profiler included servo-type accelerometers and line lasers on each side at the rear of the vehicle, and rotational encoders mounted to both rear wheels. The accelerometers provided the inertial reference for the profiler on each side, and the line lasers measured the range to ground. The profiler sensors at each side also included point lasers for measurement of the range to ground. Each point laser served as an alternative to each line laser with a faster sampling rate for verification that the line lasers were operating correctly and identification of very fine details in the longitudinal profile (e.g., cracks). Figure C-8 shows the rear view of the Nissan Altima with the profiler attached. Figure C-9 shows a close-up view of the right sensor pod with the lasers operating. Figure C- 10 shows a rotational encoder. • Longitudinal Distance Measurement: In addition to the rotational encoders at the rear wheels, the system included (1) an optical fifth wheel, (2) a Real Time Kinematic (RTK) global positioning system (GPS), and (3) monitoring of individual wheel speeds from controller area network (CAN) bus messages. Comparison of the outputs of each alternative under different measurement conditions helped verify the

C-4 calibration of the rotational encoders. Figure C-11 shows the optical fifth wheel, and Figure C-12 shows hardware from the RTK GPS. • Diagnostics: The system included several elements intended to ensure that critical sensors were providing valid readings, to verify the travel speed over each test section, and to ensure a consistent starting point for all of the runs over a given test section. This includes (1) a video-based lane tracking system, (2) a forward-looking camera, (3) CAN data from the vehicle bus for measures such as steering wheel angle, accelerator pedal, etc., (4) comprehensive outputs from an Oxford RT3050 inertial navigation system (INS) (e.g. angular rates, velocity, heading, etc.), and (5) centimeter-accurate position data from the RTK GPS system. Figure C-5. Instrumented seat pads. Figure C-6. Floor accelerometer.

C-5 Figure C-7. Accelerometer mounted to steering knuckle. Figure C-8. Instrumented Nissan Altima, rear view. Figure C-9. Right sensor pod showing line and point laser projections.

C-6 Figure C-10.Rotational encoder mounted to a rear wheel. Figure C-11.Optical fifth wheel.

C-7 Figure C-12. RTK GPS antenna and receiver. C.2.2 Physical Layout Each vehicle was equipped with the same set of instrumentation. Figures C-13 and C-14 provide a schematic of the system as it appeared on the full-sized van. Figure C-13 shows the DAS, windshield camera, lane tracker, ride sensors, rear wheel encoders, GPS antennas, and the rear sensor rack. Figure C-14 shows the top view of the hardware mounted at the lower rear of the vehicle. At the lower rear, three sensor pods are attached to an aluminum mounting plate, which serves as their “backbone.” The aluminum plate is attached to a rigid mounting plate, which is in turn attached directly to the host vehicle frame rails or body. Leveling screws allow for precise adjustment of the pod backbone. The rear bumper is removed. Figure C-13. System schematic, top view.

C-8 Figure C-14. Sensor rack, top view. Each vehicle was equipped with the same set of instrumentation, which was transferred to the next vehicle once data collection was complete. However, since each vehicle configuration was different, the precise sensor locations varied. Table C-2 lists the following sensor locations for each vehicle: • YP: This is the lateral separation of the footprint of the left and right profiler at the ground. • XPL: This is the position of the point laser footprint rearward of the center of the host vehicle rear wheel. • XLL: This is the position of the line laser footprint rearward of the center of the host vehicle rear wheel. • ZGPS: This is the height of both GPS antennas above the ground. • XGPS: This is the position of both GPS antennas forward of the line laser footprint. • YGPS, GPS: This is the position of the RTK GPS antenna leftward of the plane of vehicle symmetry. • YGPS, INS: This is the position of the INS GPS antenna leftward of the plane of vehicle symmetry. Table C-2. Sensor locations. C.2.2.1 Outer Pods Each of the left and right sensor pods carries a point laser, a line laser, and a vertically oriented servo- type accelerometer. Note that the vertical accelerometer is aligned with the centerline of the light projected by the line laser. The pods are symmetric about the longitudinal centerline of the vehicle, and the sensors are mounted so that the left and right side profilers are aligned with the center of contact of the rear tires. A separate mounting plate was fabricated for each test vehicle to provide the correct spacing of the pods. Figure C-15 shows the layout of the right pod in the rear and side view. The side view is shown without the right enclosure plate. Vehicle 2003 Nissan Altima 2013 Hyundai Tucson 2008 GMC Savana YP (in) 61.1 61.1 68.0 XPL (in) 39.8 34.1 45.7 XLL (in) 44.6 38.9 50.5 ZGPS (in) 58.0 58.0 86.6 XGPS (in) 80.3 80.3 0.0 YGPS, GPS (in) 13.4 13.8 39.4 YGPS, INS (in) -13.4 -13.8 0.0

C-9 Figure C-15. Right sensor pod. The line lasers project light over a transversely oriented line more than 4 in (100 mm) wide, with the detector rearward of the projected light source. Each line laser is mounted so that the center of the light that it projects is aligned with the sensitive axis of its companion accelerometer. The point lasers project light onto the ground over a diameter of 0.012 in (0.3 mm). The point lasers are aligned transversely with the line laser and accelerometers. Their footprint is 4.12 in (10.5 cm) forward of the line lasers, and they are mounted with the detectors inboard of the light source. When the vehicle is at rest, the line lasers have an approximate range to ground of 11.1 in (28.2 cm) and a triangulation angle of 22 degrees. The point lasers have an approximate range to ground of 11.4 in (28.9 cm) and a triangulation angle of 13 degrees. C.2.2.2 Center Pod The center pod carries an INS and an optical fifth wheel. Figure C-16 shows the layout of the center pod in the rear and side view. The side view is shown without the right enclosure plate. Figure C-16. Center sensor pod. An optical fifth wheel is mounted to the underside of the center pod for measurement of longitudinal distance. The center pod also houses the main enclosure for the INS, which contains three accelerometers, three angular rate sensors, a GPS receiver, and a CPU running a Kalman filter. (Two angular rate sensors not used in this data collection are also visible in the drawing.) line laser housing point laser housing accelerometer Side viewRear view Side viewRear view optical fifth wheel INS enclosure vehicle centerline INS enclosure

C-10 C.2.2.3 Vibration Sensors Vehicle vibration sensors included two instrumented seat pads, a floor-mounted vertical accelerometer, and two vertical accelerometers mounted to the steering knuckles. Figures C-17 through C-19 show the locations of each of these sensors and the position of the driver’s seat for each vehicle. Figure C-17. Nissan Altima ride sensor locations. Figure C-18. Hyundai Tucson ride sensor locations.

C-11 Figure C-19. GMC Savana ride sensor locations. The seating position was adjusted to a comfortable driving position, which was common to all vehicles to the extent possible. The seat bottom on the GMC Savana was not adjustable for height or angle, and the manual adjustments on the Hyundai Tucson had detents, rather than continuous adjustments. Typical driver posture is shown in Figure C-20. Figure C-20. Driver seating position in the Tucson. The servo accelerometer on the floor was oriented to measure accelerations in the vertical axis. It was placed at the longitudinal position of the driver’s pedal foot heel and in a lateral position along the driver’s

C-12 seat centerline. The carpet was cut away in order to allow rigid mounting to the floor pan using standoffs, and a shroud was fabricated to reduce the likelihood of unintentional inputs from the driver’s feet. The instrumented seat pads were designed and fabricated specifically for this project. The pads used the physical geometry specified in SAE J1013, with the exception that they each housed an IMU rather than a triaxial accelerometer. IMUs were used because they provide additional information, including rotational motion of the seat. Figure C-21 shows a top and bottom view of an unmounted seat pad. Figure C-21. Unmounted seat pad. A MicroStrain 3DM-GX4 IMU was used as the sensor element. This transducer was configured to output triaxial accelerations and triaxial angular rates in the sensor coordinate frame, and triaxial orientation using Euler angles. Seat pads were mounted to the centerline of the seat bottom per SAE J1013 and SAE J2834, below the ischial tuberosities of the driver. The seat back pad was mounted at a location on the centerline of the seat back, just below the driver’s shoulder blades. C.2.2.4 Other Sensors As shown in Figure C-13, the system includes several additional sensors: • Rotational encoders are mounted to each of the vehicle rear wheels. • A forward looking camera is mounted inside the windshield. • A MobilEye optical lane tracker system is mounted inside the windshield. • GPS antenna for the INS. • GPS antenna for the RTK system. C.2.3 Sensor Specifications Table C-3 identifies each sensor by model number and serial number. The list that follows includes pertinent specifications of each sensor as they were used in this measurement system. The RTK GPS measurements were provided by a Novatel receiver, which included a RavenX modem for receiving RTCM correction data from Network Transport of RTCM via Internet Protocol (NTRIP) servers. The INS combines measurements of acceleration, angular rate, and GPS position using Kalman filtering to estimate motion outputs. The specifications below are those listed for the RT3050 once the filter has converged. The actual outputs provide estimates of the probable error level with each set of readings. The system also includes a cellular antenna for the modem receiving Radio Technical Commission for Maritime (RTCM) correction data, which was magnetically mounted to the roof or trunk lid of each host vehicle. Although it is not shown in the diagrams, the system records wheel speeds and other pertinent quantities (transmission status, cruise control, brake light switch, etc.) from CAN bus messages.

C-13 Table C-3. System sensors. Sensor Position Make and Model Number Serial Number Left point laser LMI Selcom SLS5200/300-RO 1002 Right point laser LMI Selcom SLS5200/300-RO 2362 Left line laser LMI Selcom Gocator 2342A-3B-12 00022133 Right line laser LMI Selcom Gocator 2342A-3B-12 00022135 Left rear vertical accel. Honeywell Q-Flex QA1400-AA03-0 459 Right rear vertical accel. Honeywell Q-Flex QA1400-AA03-0 438 Driver floor vertical accel. Honeywell Q-Flex QA1400-AA03-0 450 Left knuckle accel. Summit 23200B 1080A01006 Right knuckle accel. Summit 23200B 1080A01008 Left encoder BEI XHS25-75-R2-SS-2048 QQ110792 Right encoder BEI XHS25-75-R2-SS-2048 QQ110791 Optical fifth wheel Datron DLS-2 06.303 Seat bottom IMU MicroStrain 3DM-GX4-15 6233-4220-40745 Seat back IMU MicroStrain 3DM-GX4-15 6233-4220-40743 INS Oxford Technical Solutions RT3050 073 GPS antenna, OxTS INS Novatel GPS-600-SB 01017062 NTM03230018 GPS receiver, Novatel RTK Novatel Flex6-G2L-R0G-55R NKC12240013 GPS antenna, Novatel RTK Novatel GPS-702-GG 01017577 NAE12100014 Lane tracker MobilEye C2-270 — Front camera B&H EVEMC700 — Point Lasers: • Range: 7.9 in (+/−3.9 in); 200 mm (+/−100 mm) • Resolution: 0.004 in (0.1 mm) • Bandwidth: to 2,000 Hz • Sample rate: 16,000 Hz Line Lasers: • Range: 7.9 in (+/−3.9 in); 200 mm (+/−100 mm) • Vertical Resolution: 0.00016 in (0.004 mm) • Horizontal Resolution: ~400 readings over a 3.9-in (100-mm) width at stand-off • Sample rate: ~3,240 Hz Profiler and driver floor vertical accelerometers: • Range: 4 g (+/−2 g) • Resolution: 0.0011 g • Bandwidth: to 2,000 Hz • Sample rate: 16,000 Hz Steering knuckle vertical accelerometers: • Range: 50 g (+/−25 g) • Resolution: 0.04 g

C-14 • Sample rate: 16,000 Hz Encoders: • Resolution: 2048 cycles per rev quadrature (8192 counts per revolution, which is ~0.012 in (~0.3 mm) per count) • Sample rate: recorded at 250 Hz Seat pad IMUs: • Accelerometer range: 10 g (+/−5g) all three axes • Accelerometer resolution: 0.1 mg • Accelerometer bandwidth: to 125 Hz • Gyroscope range: 600 deg/sec (+/− 300 deg/sec) all three axes • Gyroscope resolution: 0.008 deg/sec • Gyroscope bandwidth: to 125 Hz • Orientation Euler angle range: 360 degrees about all axes • Orientation Euler angle resolution: 0.01 deg • Orientation Euler angle bandwidth: 125 Hz Optical Fifth Wheel: • Velocity resolution: 0.089 ft/s (0.027129 m/s) • Velocity bandwidth: to 2000 Hz • Velocity sample rate: recorded at 16,000 Hz • Position resolution: 2 mm GPS Position (when RTK integer fix is possible): • Sample rate: 20 Hz • Accuracy: 0.04 in (1 cm) + 1 ppm of distance to base station GPS Velocity: • Sample rate: 20 Hz • Accuracy: 0.1 ft/s (0.03 m/s) root mean square (RMS) MobilEye Lateral Lane Position: • Sample rate: asynchronous • Resolution: 0.16 in (0.004 m) Forward Camera: • Sample rate: 30 images per second • Resolution: 720x480 INS Outputs: • Update rate: 100 Hz • Position Accuracy: 50 cm probable circular error • Velocity Accuracy: 0.5 mi/hr (0.8 km/hr) RMS • Acceleration bias: 0.001 g at one st. dev. • Roll/pitch: 0.04 deg at one st. dev. • Angular rate: 0.01 deg/s at one st. dev. • Bandwidth: to 400 Hz

C-15 C.2.4 Signal Flow The measurement system included a diverse set of sensors and cameras, with diverse outputs and timing. Some sensors provided serial outputs, some provided Ethernet outputs, some provided analog outputs, and others output counter values and digital signals. Data logging was performed by an embedded system including a host CPU, a counter/timer card, an analog-to-digital (A/D) card with high-speed digital inputs, a dual channel CAN bus interface, and a video frame grabber. The A/D card is connected to a custom eight- channel analog signal conditioning chassis. A high level diagram of the data acquisition system is shown in Figure C-22. Figure C-22. Signal flow. C.3 Test Procedure The same driver performed all of the data collection. The driver was selected because, in addition to having significant vehicle testing experience, he weighed approximately 175 lbs (80 kg). This driver was the closest staff member to the height and weight that appears in many publications for a “standard” human (U.S. Department of Health, European Bus Directive). Consistent driver weight and posture are particularly important because the driver and seat together behave as a system. At the start of each test day, the operator checked the cold inflation pressure of all four tires and adjusted the pressure to the proper level. The measurement system was powered for 15 minutes or more to allow the sensors to warm up. After warm-up, the operator performed several static and bounce tests to verify the operational status of the profiler accelerometers and height sensors. These tests were performed on a flat, level test pad with clipboards placed under the lasers on both sides. At minimum, the tests included a static test, a bounce test with vertical motion, and a bounce test with roll motion. Sensor data were processed to obtain profile and roughness data with a simulated travel speed of 35 mi/hr (56 km/hr).

C-16 The static tests were performed with the engine on but no external disturbances imposed on the vehicle by the operator. Bounce tests with vertical motion were conducted with upward and downward motion imposed on the rear of the vehicle while the profiler remained level. That is, the profiler assembly remained level in roll and the left and right side moved up and down together. Bounce tests were also performed with roll motion imposed on the vehicle. That is, the profiler assembly was moved out of level with the left side moving downward as the right side moved upward and vice versa. These tests verified that the sensors from each side were connected to the proper data acquisition channels. After the initial system shakedown was complete, the driver traveled for at least 10 mi (16 km) before collecting data on the test sections. This was necessary to warm up the tires and to allow the INS to “train” its Kalman filter to estimate position and velocity. The measurement system stored estimates of position accuracy by the INS and displayed them in real time. Testing proceeded at each site in the following sequence: 1. The operator initialized the DAS for the next run. At this stage, the DAS stored the section number and incremented the run number. 2. The driver approached the road segment of interest, brought the vehicle to the desired test speed, and set cruise control. 3. The operator instigated data collection prior to reaching the section starting point. 4. In advance of the section starting point, the driver “relaxed” into a standard position and posture and held the steering wheel with his hands at a standard position. 5. At the point of passing the landmark for the road segment of interest, the operator pressed an event marker button. 6. The driver maintained cruise control, a reasonably consistent position within the lane, a standard position and posture, and a standard hand position on the steering wheel for 16 seconds or more. 7. After 16 seconds of travel past the section starting point, the operator terminated data acquisition. 8. Steps 1 through 7 were repeated until three runs were collected over the test section at each of two speeds. In some cases, problems with triggering or problems maintaining the desired speed for 16 seconds in live traffic required some runs to be scrapped and repeated. The test vehicle fuel tank was filled frequently and operated with the tank more than ¾ full whenever possible. Data from each run were inspected more carefully after the testing. This included routine data quality checks, such as • verification that the vehicle passed over the entire test section in the correct lane using GPS, • inspection of profiler height sensor and accelerometer signal levels, • inspection of RMS acceleration levels and comparison to values from repeat runs, and • inspection of the recorded speed for consistency over the 16-second test interval. C.4 Test Sections The test program included 29 pavement sections on low-speed roads in urban and rural areas along 6 routes in southeastern Michigan. Table C-4 identifies the test sections from each route using the GPS coordinates of the starting point and the overall heading for 16 seconds of travel at the lowest test speed. (The “heading” values listed are actually course over ground measured clockwise from north.)

C-17 Table C-4. Test section coordinates by route. Route Section No. Starting Point Latitude (deg) Starting Point Longitude (deg) Heading (deg) Jackson Road/Huron Street 1 42.281307 −83.783493 110 2 42.280460 −83.780029 85 3 42.281536 −83.753845 93 Grand River (M−5) 4 42.348564 −83.088791 −62 5 42.386223 −83.182205 −61 6 42.408054 −83.236397 −61 7 42.415955 −83.256111 −61 8 42.414169 −83.251633 −61 Michigan Ave. (US-12) 9 42.331455 −83.070557 −90 10 42.331726 −83.055786 −90 11 42.331619 −83.062355 −93 12 42.331524 −83.087494 −91 13 42.302074 −83.263100 −109 14 42.300983 −83.267441 −108 15 42.299961 −83.271729 −107 16 42.294395 −83.309853 −106 17 42.281479 −83.396011 −97 Fort Street (M-85) 18 42.326717 −83.056801 −121 19 42.199276 −83.180519 179 20 42.195854 −83.180435 179 21 42.128914 −83.200737 −148 West Grand River 22 42.612572 −83.950447 108 23 42.608036 −83.932220 117 24 42.601597 −83.914719 117 25 42.599205 −83.908302 117 26 42.596741 −83.901672 116 27 42.595032 −83.896980 116 M-52 28 42.157814 −84.041191 178 29 42.155193 −84.041061 177 Table C-5 provides additional details about the test sections. The test sections included the functional classes 3 (principal arterial–other) and 4 (minor arterial). A majority of the sections were functional class 3. This included sections with a range of posted speed limit from 30 mi/hr (48 km/hr) to 55 mi/hr (88 km/hr). The test plan called for three passes over each section at the posted speed limit and three additional passes at a lower speed. Table C-4 lists the speed limit and the additional test speed for each section. Three runs were captured at each target speed in all 3 vehicles with the following exceptions: (1) section 12 was not tested with the Altima, (2) only 2 of the runs by the Altima at the lower test speed passed data quality checks on sections 19 and 25, (3) only 2 of the runs by the Altima at the posted speed limit passed data quality checks on section 22, and (4) passes collected by the Tucson at the lower test speed on section 29 did not include line laser readings.

C-18 Table C-5. Test section details. Section No. Direction Functional Class Speed Limit (mi/hr) Additional Test Speed (mi/hr) 1 EB 3 35 30 2 EB 3 35 30 3 EB 3 35 30 4 WB 3 35 30 5 WB 3 35 30 6 WB 3 35 30 7 WB 3 35 30 8 WB 3 35 30 9 WB 3 35 30 10 WB 3 30 25 11 WB 3 35 30 12 WB 3 35 30 13 WB 3 35 30 14 WB 3 40 30 15 WB 3 40 30 16 WB 3 40 30 17 WB 3 45 35 18 SB 3 30 25 19 NB 3 45 35 20 NB 3 45 35 21 SB 3 50 40 22 EB 4 45 35 23 EB 4 30 25 24 EB 4 45 35 25 EB 4 45 35 26 EB 4 45 35 27 EB 4 55 45 28 SB 4 30 25 29 SB 4 30 25 Most of the sections had asphalt concrete (AC) surfaces. Exceptions included brick surfaces on Sections 9 and 11, and Portland cement concrete (PCC) on Section 10, Section 19, and part of Section 17. The following are features that affected the profiles and roughness of each section: • Section 1: utility covers, close-proximity curb at the right lane edge with drainage inlets • Section 2: grades for drainage, close-proximity curb at the right lane edge with drainage inlets • Section 3: drainage inlets at the right lane edge, passage under a railway bridge • Section 4: crowned intersection crossing, passage under railway bridges, utility covers • Section 5: railroad crossing with PCC approach and leave slabs, sealed transverse and longitudinal cracks • Section 6: crowned intersection crossing, textured pedestrian crossings • Section 7: rough patching • Section 8: crowned intersection crossing

C-19 • Section 9: brick surface, crowned intersection crossing, utility covers • Section 10: utility covers, PCC joint distress, crowned intersection crossing • Section 11: brick surface, utility covers • Section 12: utility covers, intersection crossing with PCC panels, transverse cracking • Section 13: utility covers, swell at a junction to the right, grades for drainage, transverse cracking • Section 14: grades for drainage, close-proximity curb at the right lane edge with drainage inlets, patching, transverse cracking • Section 15: PCC crosswalk, crowned intersection crossing, utility covers, close-proximity curb at the right lane edge • Section 16: crowned intersection crossing, bump at a transverse crack • Section 17: passage under railway bridge, AC-to-PCC transition, sealed paving lane joint, sealed transverse cracks, close-proximity curb at the right lane edge with drainage inlets • Section 18: utility covers, crowned intersection crossing, high-severity block cracks that are sealed • Section 19: close-proximity curb at the right lane edge with drainage inlets • Section 20: close-proximity curb at the right lane edge with drainage inlets, swells at junctions to the right, close-proximity driveways to the right • Section 21: railroad crossing • Section 22: drainage inlets at the right lane edge, swells at junctions to the right • Section 23: crowned intersection crossing, intersection crossing with PCC panels, textured pedestrian crossings • Section 24: passage under a railway bridge, utility covers, grades for drainage, close-proximity curb at the right lane edge with drainage inlets • Section 25: crowned intersection crossing, rutted intersection approach, transverse cracks, close- proximity curb at the right lane edge • Section 26: sealed transverse cracks, close-proximity curb at the right lane edge with drainage inlets • Section 27: sealed transverse cracks, sealed longitudinal cracks in the left wheel path, grades for drainage, close-proximity curb at the right lane edge • Section 28: utility covers, swells at junctions to the right • Section 29: utility covers C.5 References “Weight, Height, and Selected Body Dimensions of Adults. United States 1960-1962.” U.S. Department of Health, Education, and Welfare Publication No. (HRA) 76-1074. “Height and Weight of Adults Ages 18-74 Years by Socioeconomic and Geographic Variables. United States.” U.S. Department of Health and Human Services Publication No. (PHS) 81-2674. “Weight and Height of Adults 18-74 Years of Age: United States, 1971-1974.” U.S. Department of Health, Education, and Welfare Publication No. (PHS) 79-1659. European Bus Directive 2001/85/EC, part 7.4.2.1.

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S. DOT United States Department of Transportation

TRA N SPO RTATIO N RESEA RCH BO A RD 500 Fifth Street, N W W ashington, D C 20001 A D D RESS SERV ICE REQ U ESTED ISBN 978-0-309-48060-4 9 7 8 0 3 0 9 4 8 0 6 0 4 9 0 0 0 0 N O N -PR O FIT O R G . U .S. PO STA G E PA ID C O LU M B IA , M D PER M IT N O . 88