2.4 Nonmotorized Facilities Analysis

Introduction to Nonmotorized Facilities

In modern transportation engineering, facility design and evaluation have shifted from purely vehicle-centric metrics to multimodal analysis. The Highway Capacity Manual (HCM) provides guidelines for evaluating the performance of nonmotorized facilities, specifically focusing on pedestrian and bicycle operations. Analyzing these facilities is essential for creating safe, complete streets, and is a key topic on the NCEES PE Civil Transportation exam.

Pedestrian Walkway and Sidewalk Analysis

The operational analysis of pedestrian walkways evaluates sidewalks, paths, and plazas. The performance is assessed using pedestrian speed, flow rate, and density. The primary service measure for walkways is pedestrian space ($M$), measured in square feet per pedestrian ($ft^2/ped$).

Effective Sidewalk Width ($W_E$)

Pedestrians do not use the entire physical width of a sidewalk. Part of the sidewalk is occupied by physical obstructions (benches, trees, light poles, parking meters), and pedestrians naturally maintain a "shy distance" from building walls and roadway curbs. The effective sidewalk width ($W_E$) is calculated as:

W_E = W_T − W_O

Where:

• W_T = Total physical width of the sidewalk (ft).
• W_O = Width of obstructions plus shy distances (ft). Standard shy distance offsets include 1.5 ft from building faces and 1.0 to 1.5 ft from curbs.

Pedestrian Unit Flow Rate (v_p)

The pedestrian flow rate represents the number of pedestrians passing a point per unit of width per minute. It is calculated as:

v_p = V_p / W_E

Where:

• v_p = Pedestrian unit flow rate (ped/min/ft).
• V_p = Pedestrian volume (ped/min).
• W_E = Effective sidewalk width (ft).

Pedestrian Speed (S_p) and Space (M)

• Walking Speed (S_p): The average walking speed under unimpeded conditions is typically taken as 4.0 ft/s (240 ft/min). For design purposes, particularly signal timing, a speed of 3.5 ft/s is used to accommodate slower pedestrians, such as children and older adults.

• Pedestrian Space (M): The average area available to each pedestrian, calculated as the inverse of density. It is computed from walking speed and flow rate:

  M = (S_p × 60) / v_p

  Where S_p is in ft/s and v_p is in ped/min/ft. (For example, if S_p = 4.0 ft/s and v_p = 20 ped/min/ft, then M = 240 / 20 = 12.0 sq ft/ped).

Pedestrian Level of Service (PLOS) for Walkways

The PLOS for sidewalks is determined directly by the average pedestrian space (M):

Pedestrian Platoon Flow

In urban environments, pedestrians do not arrive uniformly. They frequently travel in platoons (groups) due to traffic signal releases or transit arrivals. Platoon flow analysis evaluates the localized peak density within the group. The platoon flow rate is higher than the average hourly flow rate, resulting in a significantly smaller pedestrian space. HCM guidelines suggest using platoon flow rates for high-density transit corridors and CBD areas to ensure adequate sidewalk sizing.

Crosswalk Design and Signal Requirements

At intersections, crosswalks must accommodate pedestrians waiting to cross and those crossing during the green phase.

Pedestrian Clearance Time (t_p)

The traffic signal must provide sufficient green time (or flashing "Don't Walk" time, known as the Pedestrian Clearance Interval) to allow a pedestrian starting from the curb to cross the entire width of the street. The required clearance time is calculated as:

t_p = d_c / S_p

Where:

• d_c = Pedestrian crossing distance, measured from the curb to the center of the farthest travel lane (ft).
• S_p = Walking speed (typically 3.5 ft/s per the MUTCD standard).

Additionally, the MUTCD requires a minimum Walk Interval (t_w) of 7.0 seconds (which can be reduced to 4.0 seconds in rare cases) to allow pedestrians to step into the crosswalk before the clearance interval begins.

Corner Storage Area

Intersection corners serve as storage reservoirs for pedestrians waiting for a walk signal. The corner reservoir capacity is analyzed based on the available area and the peak number of waiting pedestrians, targeting a minimum of 5.0 to 10.0 sq ft per pedestrian to maintain acceptable operations.

Bicycle Level of Service (BLOS)

Unlike vehicular or pedestrian LOS, which are determined by physical service measures like delay or space, Bicycle Level of Service (BLOS) is a model-based index that represents the average bicyclist's perception of comfort and safety on a roadway segment.

Factors Influencing BLOS

The BLOS score is calculated using regression models based on empirical passenger studies. Key factors include:

• Bicycle Lane Width: Wider bike lanes, paved shoulders, and outside travel lanes significantly improve comfort.
• Motorized Vehicle Volume and Speed: High volumes and higher travel speeds of adjacent vehicles reduce comfort.
• Heavy Vehicles: A higher percentage of trucks/buses decreases bicyclist comfort due to wind turbulence and perceived risk.
• Pavement Condition: Roadway surface roughness (represented by the Pavement Condition Index, PCI) has a substantial impact; rough or cracked pavement reduces bicyclist comfort.