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Publication Number: FHWA-HRT-04-103
Date: October 2004

Characteristics of Emerging Road and Trail Users and Their Safety

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FIELD DATA COLLECTION PLAN

This study evaluated the following characteristics of emerging road and trail users:

  • Physical dimensions: length, width, height, eye height, wheelbase, wheel spacing, wheel diameter, tire/wheel width, tire type.
  • Space required for three-point turn.
  • Lateral operating space (sweep width).
  • Turning radii.
  • Acceleration capabilities.
  • Speed.
  • Stopping sight distance: perception / reaction (time) and braking distance.
Figure 16. Photo. Pinellas Trail, St. Petersburg, FL. This photo shows the Pinellas Trail in St. Petersburg, FL. It is a paved trail in full sun with a trees on one side. One bicyclist is on trail. A data collection event was held here on January 25, 2003.
Figure 16. Pinellas Trail, St. Petersburg, FL.
Data were collected at three data collection ("Ride for Science") events held in 2003: Pinellas Trail in St. Petersburg, FL (January 25, 2003); Paint Branch Trail in College Park, MD (May 3, 2003); and San Lorenzo River Trail in Santa Cruz, CA (June 13, 2003) (figures 16-18).

Figure 17: Photo. Paint Branch Trail, College Park, MD. This photo shows the Paint Branch Trail in College Park, MD. A paved trail winds through a heavily wooded area. A data collection event was held here on May 3, 2003. Figure 18: Photo. San Lorenzo River Trail, Santa Cruz, CA. This photo shows the San Lorenzo River Trail in Santa Cruz, CA. It is an open trail with a large grassy area on one side. The other side gives way to a gentle embankment. One bicyclist is on the trail. A data collection event was held here on June 13, 2003.

Figure 17. Paint Branch Trail, College Park, MD. Figure 18. San Lorenzo River Trail, Santa Cruz, CA

In addition to being geographically dispersed, the event sites met several other criteria including:

  • Portions of the trails functioned at unconstrained levels of operation.
  • The trails were relatively flat and the observation stations were not influenced by grades.
  • There was sufficient space along the sides of the trails to set up observation stations.
  • The trails were within metropolitan areas.
  • The event sites were located adjacent to large, flat, smooth paved surfaces that could accommodate the turning radius station.
Figure 19: Graphic. Typical layout of data collection stations (San Lorenzo River Trail). Data were collected by observing study participants at seven data collection stations. This graphic shows the layout of a data collection station that was setup for the San Lorenzo River Trail. A blue line with arrows at each end runs vertical on the left side of the diagram. This indicates a portion of the trail that was used. Stations 4 (Acceleration Station), 5 (Sweep Width Station), 6 (Speed Station), 7 (Deceleration Station), and End Event Point are all indicated along this line. A lighter blue line runs perpendicular and intersects the trail at the top. This is Water Street. Water Street is intersected by Ocean Street which runs parallel to the trail. In the space between the trail and Ocean Street, there is a parking lot and registration stations 1 (Physical Characteristics), 2 (Turning Station), and 3 (Turning Radii) are indicated.
Figure 19. Typical layout of data collection stations (San Lorenzo River Trail).

Data were collected by observing trail users at seven stations (figure 19). The trail users consisted of both active and in situ (passive) participants (figure 20). Active participants were those who either were intercepted on the shared use path (via event signage; see figure 21) or responded to the public outreach program and specifically traveled to the location to actively participate in the data collection event. They were recruited through contacts with mode specific clubs (inline skaters, skateboarders, Segway users), seniors' centers, and schools. Flyers were placed in sporting goods stores and parks. Advocacy groups for disabled individuals were also contacted. Active participants registered with the data collection team and generally progressed through all the data collection stations. In situ participants were those who were on the shared use path just "passing through" the event stations. Thus, at all seven stations, data were collected from active participants. At two stations, speed and lateral operating space, data were also collected on in situ participants.

Figure 20. Trail users consisted of both active and in situ participants Figure 20: Photo. Trail users consisted of both active and in situ participants. There are two bicyclists riding on this trail. One is wearing a bib with a number on it, indicating that he is an active participant. The other is not wearing a bib, indicating that he is an in situ participant. Figure 21: Photo. Trail user intercept signage. Signs were placed on the trails to intercept trail users and encourage them to participate in the data collection events. The sign shown in this photo invites trail users to participate and provides information about who can ride, when and where, and details. Figure 21. Trail user intercept signage.

A total of 551 in situ participants and 260 active participants were observed at the three events (table 5) for a total of 811 participants.

Table 5. Active and in situ participants at each event.

  CALIFORNIA FLORIDA MARYLAND TOTAL
Active 95 81 84 260
In situ 193 210 148 551
Total 288 291 232 811

Age and gender were obtained for many of the active participants. The ages ranged from 5 to 88, and the breakdown by equipment type is shown in table 6.

Table 6. Gender distribution and ages of active participants.

USER TYPE N (by gender) MALE FEMALE N (by age) MEAN AGE (years)
Bicycle 115 57% 43% 114 39
Hand cycle 21 52% 48% 20 33
Inline skates 20 65% 35% 21 37
Kick scooter 7 43% 57% 7 25
Manual wheelchair 7 86% 14% 7 46
Power wheelchair 5 80% 20% 6 48
Recumbent bicycle 6 100% 0% 5 52
Other 8 50% 50% 8 36

Figure 22: Photo. Video cameras were setup to record participant movements at Stations 3 through 7. A bicyclist is riding through the deceleration station. An event staff person adjacent to the trail is holding up a STOP sign. A video camera is mounted adjacent to the trail and is filming the bicyclist's reaction to the STOP sign.
Figure 22. Video cameras were setup to record participant movements at Stations 3 through 7.

The physical characteristics (Station 1) and three-point turn widths (Station 2) were measured using tape measures. Synchronized video cameras were set up to record participant movements at the other stations (figure 22). Several types of video logging, including digital video, were employed to capture and document the operational characteristics of emerging road and trail users and their safety. The accurate and precise video documentation of the user groups was essential to the success of this study. As technology has advanced, digital data collection equipment has become more economical and productive. Thus digital technology was used at all stations to ensure optimized precise viewing, timing, and subsequently convenient downloading of data. Highly specialized audio-visual staff was directed by the Assistant Principal Investigator to provide the technical setup, supervision, and maintenance of the video-based stations to ensure maximum efficiency. This decreased the margins for error, assuring a complete one-time setup (after the pilot testing, of course).

Another important consideration in planning data collection was the methodology employed at each survey data station. Each station was preliminarily designed and extensively pilot tested, considering any earlier research and developing several options for data collection techniques (figure 23). During the subsequent data reduction and analysis portions of the study, because all data had been collected digitally, the data could be computer interfaced to streamline the data reduction and analysis times.


Figure 23: Photos. Equipment testing at data collection stations. This is a mosaic of five photos. Photo 23a: A bicyclist riding through the acceleration station. He is being filmed by a video camera mounted adjacent to the trail. Photo 23b: A close-up view of the video camera. Photo 23c: A close-up view of a table with a VCR and a video monitor on it. Photo 23d: An inline skater traveling through the acceleration station. He is being filmed by a camera mounted adjacent to the trail. Photo 23e: An event staff person checking equipment alongside the trail.

A precursor to determining equipment needs was an understanding of the objective (operational consideration) of each station, the station's unique data objectives, and, ultimately, the design application of the information. Accordingly, the survey station designs, data collection, and analysis was planned in a comprehensive manner so that future facilities design can be done more accurately and that the safety of road and trail users will be enhanced.

Figure 24: Photo. Temporary pavement markings were tested. Three event staff persons are measuring the distances between the longitudinal lines at the sweep width station.
Figure 24. Temporary pavement markings were tested.

This applications-focused backdrop helped determine the specific equipment used at each station. Each station also required extensive pilot testing and technical analysis of equipment options from the video recording media to the quad synchronization communication devices. Various temporary pavement markings (for data reduction reference) were tested to maximize data reduction accuracy while minimizing effects to normal trail operations (figure 24). Following each data collection event, the videotapes were converted to digital format and subsequently viewed to reduce the data and determine operational characteristics, as described below for each of the seven stations.

Registration desks were established for each data collection event (figure 25). Participants who responded to the outreach campaigns or trail intercept signage signed in and were given a briefing on the purpose of the study, an overview of the event and course, and safety provisions.


Figure 25. Registration desk.

Station 1-Physical Characteristics

At the first station, the physical characteristics of active participants and their equipment were measured (figure 26). These included:

Figure 25: Photo. Registration desk. One participant is talking to two event staff persons at the registration desk. Other participants are standing nearby.
a. Physical measurements of a wheelchair and rider.
Figure 26: Photos. Physical measurements. Photo 26a: Two event staff persons are measuring the height of a participant in a manual wheelchair. Photo 26b: Two event staff persons are measuring the length of a bicycle and the width of the bicyclist. Two other bicyclists wait their turn.
b. Physical measurements of a bicycle and rider.
Figure 26. Physical measurements.
  1. Length-measured parallel to the direction of travel, including the user's body, if applicable.
  2. Width-measured perpendicular to the direction of travel, including the user's body if it extends beyond the device or vehicle.
  3. Height-measured from the ground to the highest point on the device or vehicle or the top of the user's head, whichever is higher.
  4. Eye height-measured from the ground to the user's eye location.
  5. Wheelbase-measured between the front axle and the rear axle of the device or vehicle.
  6. Wheel spacing-measured from the center of one outside wheel to the center of the other outside wheel.
  7. Wheel diameter-measured vertically from the point of contact with the ground to the highest point on the wheel.
  8. Tire or wheel width.
  9. Tire type (pneumatic, polyurethane, solid rubber, etc.)

These physical dimensions can be used by practitioners to provide an assessment of users' operational characteristics and facility design features that are critical to some user groups. For example, pavement condition requirements for a user group depend on the size and type of wheels and tires of the device or vehicle. Large-wheeled vehicles and devices like bicycles and jogging strollers can be used on a variety of pavements. Small-wheeled devices like skateboards, inline skates, and kick scooters are nearly impossible to use on unpaved surfaces and can be uncomfortable and difficult to operate on rough pavements such as chip seal and asphalt with large aggregate. Similarly, pavement condition is a factor in wheelchair travel. Manual and powered wheelchairs that are built to optimize indoor maneuvering will not be as usable in the outdoor environment.

For motorized scooters, wheelchairs, and other assistive devices, the critical measurement is width, which is necessary to determine the minimum clear width for passage. Section 4.2.1 of the ADAAG requires a minimum clear width of 815 mm (32 inches) at a point, and 915 mm (36 inches) continuously, for single wheelchair passage. In addition, Section 4.2.2 of the ADAAG requires that the minimum width for two wheelchairs to pass is 1525 mm (60 inches).

Maneuvering around a turn requires additional space for wheeled devices. Where bollards, fences, gates, or turnstiles restrict access to shared use paths, users may have difficulty getting their devices through the restricted area. The results of this research will help provide facility designers with the information needed to design for both accessibility and safe operation.

Station 2-Three-Point Turn

A three-point turn is defined as a maneuver where the user starts at one edge of the shared use path, makes a forward turn toward the other side of the path, backs up while turning the device or vehicle in the other direction, and then makes a forward turn in the original direction to complete the 180-degree turn. Designers can use this information to select shared use path widths and, if necessary, build wider turnaround areas, so that users can execute U-turns within the confines of the path. To make a U-turn, bicyclists can dismount, pick up their bikes, turn them around, get back on, and ride off in the desired direction. This is often not possible for people with mobility impairments, or other users. Instead, they must be able to turn around in their manual or powered wheelchair, hand cycle, or other device within the confines of the traveled way. However, the turning radius of these devices can make it difficult or impossible for a user to make a U-turn on a narrow shared use path. For example, it was discovered in this research that a hand cyclist can require 4.5 m to 6 m (15 ft to 20 ft) to make a U-turn. In these situations, a multipoint turn is necessary.

At this station, active participants were asked to make a three-point turn and the width that they required was measured (figure 27).

Figure 27: Graphic. Three-point turn. This graphic illustrates a three-point turn. The drawing shows a wheelchair from an overhead view and its movement is indicated by sweeping lines wit arrows showing direction of movement. A person in a manual wheelchair starts at one edge of a trail, makes a forward turn toward the other edge of the trail, backs up while turning his wheelchair in the other direction, and then makes a forward turn in the original direction to complete a 180-degree turn.
Figure 27. Three-point turn.

Station 3-Turning Radii

Typical turning radii are critical in determining the horizontal alignment of roads and shared use paths. A bicyclist leans inward (toward the center of a curve) and is likely to slow down while rounding the curve so that he/she does not fall outward due to centrifugal force. The extent of the lean, as measured from the perpendicular, is the lean angle. As the turning radius increases, the bicyclist does not have to lean as much to overcome centrifugal force, holding speed constant. Alternatively, a higher turning radius means that the bicyclist can maintain the same lean angle and travel around the curve at a faster speed. For bicycles, AASHTO (p. 38) recommends a minimum radius of 12 m (36 ft) for a design speed of 20 km/h (12 mi/h), increasing to a minimum radius of 74 m (225 ft) for a design speed of 50 km/h (30 mi/h).(2) This recommendation is based on a 15-degree lean angle.


Figure 28: Photo. Participant within turning radii station. A participant is riding a hand cycle through a curved turning path delineated in a parking lot.
Figure 28. Participant within turning radii station.

Only active participants were used for the turning radius measurements. Turning paths with predetermined radii were delineated in a large paved area (figures 28 and 29).

Careful briefing was done to ensure that participants understood the testing procedure (figure 30).

Several research staff oversaw the stations at the various events to ensure proper participant flow-through (figure 31). The participants traveled through the largest radius path first (figure 32). They repeated the process on paths with progressively smaller radii (figure 33). The multiple-synchronized cameras enabled multiperspective time-stamped videoing of active participants as they went through each radius. The composite video was subsequently viewed to determine the times that participants entered and exited each radius. The data entry spreadsheet was set up to calculate the average speeds, based on these recorded times, as participants traveled through each radius.


observer/ elevated camera setup Figure 29: Graphic. Turning radius layout (not to scale). Six turning paths with predetermined radii are delineated. The briefer/starter stands in front of the turning path with the largest radius. Four elevated cameras are strategically positioned around the turning paths so that participants who are traveling through any of the turning paths are filmed by one or more cameras.
Figure 29. Turning radius layout (not to scale).

Figure 30: Photo. The participants were briefed at the turning radius station. An event staff person is briefing a participant on a bicycle.
Figure 30. The participants were briefed at the turning radius station.



Figure 31: Photo. Research staff oversaw the turning radius station to ensure proper participant flow-through. A participant on a bicycle is riding through a turning path. An event staff person is watching him and directing him toward the next turning path. Figure 32: Photo. A participant traveling through the largest radius path. A participant on a bicycle is riding through the turning path with the largest radius.Figure 33: Photo. Participants traveling through progressively smaller turning radii. A participant on a nonmotorized kick scooter is traveling through the turning path with the second smallest radius. In the background, another participant on a nonmotorized kick scooter is approaching the turning path with the fourth smallest radius. They are riding on a black topped parking lot where lines have been placed to indicate the arc of the curve in which participants should travel.

Station 4-Acceleration

The acceleration rate is defined as the time that it takes for a user to accelerate from a stopped position to a normal cruising speed. Practitioners use acceleration rates to calculate gap acceptance and the necessary intersection sight distance. This is especially important at intersections of shared use paths and roadways where path users are stopped and waiting to cross the roadway. Path users must correctly judge whether gaps in oncoming traffic provide sufficient time to cross the roadway safely, based on the speed of oncoming motor vehicles, their own acceleration capabilities, and the width of the roadway to be crossed.

Figure 34: Photo. Participants accelerated along a 60-meter (200-foot) section of the course. A participant on a recumbent bicycle is accelerating to his normal riding speed. This section of the course is marked with transverse lines that are 12.2 meters (40 feet) apart.
Figure 34. Participants accelerated along a 60-m (200-ft) section of the course.

Acceleration capabilities were measured for active participants. The acceleration data were collected using time-stamped video to determine the elapsed time for the participants accelerating along a 61-m (200-ft) section of the course (figure 34). This section was further subdivided into lines at 12.2-m (40-ft) spacings. Participants were asked to accelerate to their normal running speed (figures 35 and 36). The time when each participant crossed each transverse line was recorded.

Figure 35: Photo. Participants were asked to accelerate to their normal speed. An event staff person is instructing two participants - one on a bicycle and one on a hand cycle - at the acceleration station.
Figure 35. Participants were asked to accelerate to their normal speed.
Figure 36: Photo. A skateboarder starting to accelerate. A participant is stepping onto his skateboard and preparing to leave the deceleration station.
Figure 36. A skateboarder starting to accelerate.

Station 5-Lateral Operating Space (Sweep Width)

Space requirements of transportation users are one of the essential inputs in facility design, particularly in determining cross-sectional dimension needs of facilities. The Highway Capacity Manual(26) outlines the levels of service for shared use paths from the perspective of bicyclists, keying on the calculation of passing hindrance,(27) an operational condition affected by relative speed differentials, acceleration rates, and physical space requirements among bicyclists and pedestrians. The proportion of inline skating and other emerging transportation and recreational modes is rapidly increasing on our Nation's shared path facilities. Thus, over time, if the trend continues, the approach of using only bicyclist and pedestrian user groups, as outlined in chapter 11 and 19 of the 2000 Highway Capacity Manual (HCM), to determine a shared use path's level of service (hence design width) may result in under-designed or undersized transportation facilities.

User densities within a transportation facility can often influence the space occupied by the various emerging users (Fruin, as referenced in the HCM 2000). For example, for inline skaters and perhaps scooter operators, as the operating conditions become congested, people's freedom to maneuver becomes constrained and speeds decrease, and the operational space occupied by the user may decrease. Accordingly, researchers focused the survey design, hence data collection, of space dimensions to actual occupied horizontal and vertical dimensions of users operating within uncrowded pathway operating sections of the shared use paths.

Lateral operating space (or "sweep width") is the width needed by the user to operate in a safe manner under normal conditions. In general, this width is much greater than the measured width of the user in a stopped position. This is especially the case for inline skaters. A person who swerves left and right (such as an inline skater) will occupy more lateral space, and have a wider sweep width, than a person whose movements are parallel to the edges of the trail (such as a bicyclist). Both the tread and max values of sweep width were recorded. The tread is the width of the contact(s) with the ground. For example, the tread of a bicycle is the width of its tires. The tread of a wheelchair is the width from the outer edge of the left tire to the outer edge of the right tire. The max includes the width of the user. For example, a young child bicyclist will have a narrower max than an overweight adult bicyclist. The tread and max values also vary with the path that the participants follow while traveling through this station. A person has wider tread and max values if he/she travels diagonally from the left edge to the right edge of the trail than if he/she travels straight down the middle, parallel to the edges of the trail. Determining the lateral operating space of each user group at varying speeds is important for determining appropriate shared use path widths, given knowledge of trail user volumes and application of the level of service methodologies in the Highway Capacity Manual as calibrated in FHWA's recent "Operation of Shared Use Paths" study.

At each event, a section of trail was marked with longitudinal lines (figures 37 and 38). Both active and in situ participants were videotaped as they traveled through this section. The video was subsequently reviewed to determine the tread and max values for each participant.

Figure 37: Photo. Sweep width station. A participant using inline skates has skated through the sweep width station. This section of trail is marked with longitudinal lines spaced 1 meter apart.
Figure 37. Sweep widths station.
Figure 38: Graphic. Sweep width and speed. This drawing shows an overhead view of a section of trail marked with longitudinal lines that are 8 meters long and spaced 1 meter apart. Transverse lines mark the beginning and end of the sweep width and speed station. An overhead video camera is films participants as they travel through this station. An observer is stands alongside the trail.
Figure 38. Sweep width and speed.

Station 6-Speed

Speed is defined as the normal cruising speed of users on a flat, smooth section of a shared use path. The speed characteristics of emerging road and trail users are generally influenced by age, gender, experience, weather and pavement conditions, operating conditions, and facility geometrics.(8) Practitioners can use typical cruising speeds to develop design speeds for each user group. Design speed is critical in determining horizontal and vertical alignments. Speed is also used in calculating necessary sight distances.

Time-stamped video was obtained of both active and in situ participants as they traversed the section of trail marked with lateral lines within Station 5 (figure 39). The video was subsequently reviewed to determine the times that participants crossed each of the two lines. The data entry spreadsheet was set up to calculate the average speeds based on these recorded times.

Figure 39: Photo. Speed (and sweep width) station. This is a photo of what actually took place as represented by the drawing in figure 38. We see a section of trail is marked with longitudinal lines spaced 1 meter apart. A participant on a hand cycle is travels through this station. Transverse lines mark the beginning and end of the sweep width and speed station. An overhead video camera is films him. An event staff person is sits at a table and observes the participant.
Figure 39. Speed (and sweep width) station.

Station 7-Stopping Sight Distance (Deceleration)

Stopping sight distance is the total distance traversed by a user between the point where he/she recognizes the existence of an object or situation that requires a stop and the point where he/she has come to a safe stop. This is perhaps one of the most widely used user characteristics in the design of transportation facilities. Stopping distance is based on two components: the distance traveled by the user during his/her perception and reaction time plus the distance required to physically brake to a stop. Accordingly, the stopping distance station was designed to capture both characteristics. The first, the distance traveled during the users' perception and reaction time, was captured with a digital video log similar to the physical setup of the speed studies. Subjects were videoed (from multiple camera positions, see figure 40) within a segment of the shared path. The duration (using a synchronized time display on the video frames) and distance traveled from the "stop" signaling for our downstream-positioned staff to the users' physical commencement of braking was captured on synchronized videos and later reduced by analysis of the video logs. This approach was different from that used by Birriel et al.(8) and Brown,(28) who documented only the braking component of the stopping distance action.

Figure 40: Graphic. Stopping sight distance. This drawing shows an overhead view of a section of trail marked with longitudinal and transverse lines to form a 1-meter reference grid. The total length is 40 meters. An event staff person holds a STOP sign is standing alongside the trail, waiting for a participant to enter the stopping sight distance station. Five video cameras are mounted alongside the trail, spaced 8 meters apart.
Figure 40: Graphic. Stopping sight distance.

The research team surveyed the second component of stopping sight distance, the actual braking distance, in the following manner. As shown in figure 41, several video cameras were positioned at strategic points around the braking test area. This portion of the camera setup was similar to the methods pioneered by Birriel et al.(8) Data reduction and calculations were done in a similar fashion to that for the perception-reaction component.

Figure 41: Photo. This is a photo of what actually took place as represented by the drawing in figure 40. Several video cameras were positioned at strategic points around the braking area. This section of trail is marked with longitudinal and transverse lines to form a 1-meter reference grid. An event staff person is sitting alongside the trail and is getting ready to raise a STOP sign. Another event staff person is sitting at a table alongside the trail and is watching the two video monitors. A video camera is mounted nearby.
Figure 41. Several video cameras were positioned at strategic points around the braking area.

AASHTO defines stopping sight distance as:

Equation 1: d equals 0.278Vt plus 0.039 times the result of V squared over a.      (1)

where: d = stopping sight distance

t = brake reaction time, seconds

V = design speed, km/h

a = deceleration rate, m/sec2 (29)

The first term in the above equation is the distance traveled during the user's brake reaction time.

AASHTO uses a brake reaction time of 2.5 seconds for bicyclists.(2) It is entirely possible that other user groups have different brake reaction times. Of course some variation in brake reaction times is likely among the individuals within each user group. The second term in the equation is the braking distance, defined as the distance traveled once the user applies the brakes and before he/she comes to a stop.

Figure 42: Photo. STOP sign controller signaling a bicyclist to stop. A participant is riding her bicycle through the stopping sight distance section. An event staff person is holding up a STOP sign to signal the participant to stop 'as quickly as is comfortable.'
Figure 42: Photo. STOP sign controller signaling a bicyclist to stop.

Only active participants were used for stopping sight distance. During the registration briefing, participants were told that at some point along the course they may be presented with a STOP sign, and if so, they were to stop as "quickly as is comfortable." There were several points along the shared use path where the pavement was marked with a 1 m reference grid on the approach to a "dummy" STOP sign controller. This was done to minimize the participants' anticipation of where the stopping maneuver was to occur. The layout of the actual stopping station is shown in figure 40. An orange cone was placed 30 m (100 ft) in advance of the STOP sign controller to mark the AASHTO stopping sight distance for a bicyclist traveling at 30 km/h (20 mi/h). At various points before the participant reached the cone, the STOP sign controller signaled for the participants to initiate their stop (figure 42).

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