7.5 Multimodal Geometric Design: Pedestrian Facilities, Bikeways, & ADA

7.5 Multimodal Geometric Design: Pedestrian Facilities, Bikeways, & ADA

PTOE Exam Focus: Multimodal questions evaluate candidates on ADA / PROWAG accessibility controls (PAR width $\ge 4.0\text{ ft}$, cross-slope $\le 2.0%$, curb ramp running slope $\le 8.33%$ or $1:12$, landing dimensions $\ge 4.0\text{ ft} \times 4.0\text{ ft}$, detectable warning depth $24\text{ in.}$), pedestrian clearance interval calculations ($D / 3.5\text{ ft/s}$), refuge island dimensions ($W \ge 6.0\text{ ft}$), and protected bike lane intersection setbacks ($6.0\text{--}16.5\text{ ft}$).

1. PROWAG / ADA Geometric Standards for Pedestrian Facilities

The Public Rights-of-Way Accessibility Guidelines (PROWAG) establish binding geometric design standards for pedestrian facilities within the public right-of-way:

+-------------------------------------------------------------------------------------+
|                        PROWAG ACCESSIBILITY GEOMETRIC CONTROLS                      |
+---------------------+-----------------------+---------------------------------------+
| Geometric Element   | PROWAG Mandate        | Engineering Design Rationale          |
+---------------------+-----------------------+---------------------------------------+
| Pedestrian Access   | Min 4.0 ft clear      | Accommodates single wheelchair;       |
| Route (PAR) Width   | (5.0 ft standard)     | 5.0 ft allows two wheelchairs to pass |
+---------------------+-----------------------+---------------------------------------+
| PAR Passing Spaces  | 5.0 ft x 5.0 ft every | Required if continuous PAR width      |
|                     | 200 ft interval       | is less than 5.0 ft                   |
+---------------------+-----------------------+---------------------------------------+
| PAR Cross-Slope     | Max 2.0% (1:50)       | Prevents lateral wheelchair drift /   |
|                     | (nominally 1.5%)      | asymmetric upper-body exertion        |
+---------------------+-----------------------+---------------------------------------+
| PAR Running Grade   | Equal to roadway grade| On standalone paths, grade <= 5.0%    |
|                     | (or <= 5.0% off-road) | (1:20); if steeper, treat as ramp     |
+---------------------+-----------------------+---------------------------------------+
| Curb Ramp Running   | Max 8.33% (1:12)      | Maximum slope accessible for manual   |
| Slope               |                       | wheelchair ascent                     |
+---------------------+-----------------------+---------------------------------------+
| Curb Ramp Landing   | Min 4.0 ft x 4.0 ft   | Level turning / resting platform      |
| (Top / Intermediate)| (Max 2.0% cross-slope)| prior to entering travel way          |
+---------------------+-----------------------+---------------------------------------+
| Detectable Warnings | 24 in. depth (full    | Truncated domes alerting visually     |
| (Truncated Domes)   | width of opening)     | impaired users to vehicular boundary  |
+---------------------+-----------------------+---------------------------------------+

                         PROWAG CURB RAMP & LANDING GEOMETRY

                  Continuous Sidewalk (PAR: Cross-Slope <= 2.0%)
         =================================================================
                              |                      |
                              |   LANDING PLATFORM   | <-- Min 4.0 ft x 4.0 ft
                              | (Slope <= 2.0% all)  |     (5.0 ft x 5.0 ft pref)
                              +----------------------+
                             / |                    | \
                            /  |     RAMP RUN       |  \ <-- Flare Slope <= 10.0%
                           /   | (Running <= 8.33%) |   \    (1:10 for pedestrian
                          /    | (Cross-S <= 2.0%)  |    \    traverse)
                         /     |                    |     \
                        +======+====================+======+
                        |  ::: TRUNCATED DOMES (24" Depth):|
         ---------------+----------------------------------+---------------
                        Gutter / Traveled Way (Counter Slope <= 5.0%)

Critical Ramp & Flare Details:

• Curb Ramp Flares: When a curb ramp is located where pedestrians may walk across the ramp side (e.g., in a continuous concrete sidewalk), side flares must have a maximum slope of $10.0%$ ($1:10$) (or $8.33%$ if landing is constrained) to prevent tripping hazards. If the ramp is bordered by grass or a planting strip, vertical curbs may replace flares.
• Counter Slope (Gutter Slope): The algebraic difference between the curb ramp running slope ($8.33%$) and the gutter counter slope must not exceed $13.33%$ (maximum gutter slope $5.0%$) to prevent wheelchair footrests from catching on the transition point.

Pedestrian Crossing Safety Treatments & Physical Geometric Controls

2. Pedestrian Clearance Time & Crossing Calculations

In accordance with the MUTCD (Section 4I.06), total pedestrian crossing time ($T_{\text{ped}}$) is calculated using standardized kinematic walking speed parameters:

$T_{\text{ped}} = t_{\text{walk}} + t_{\text{clearance}} = t_{\text{walk}} + \frac{D}{S_{\text{walk}}}$

Where:

• $t_{\text{walk}}$ = Walk interval (minimum $7.0\text{ seconds}$; $4.0\text{ seconds}$ permitted under special engineering judgment)
• $t_{\text{clearance}}$ = Flashing Don't Walk (FDW) pedestrian change interval (seconds)
• $D$ = Pedestrian crossing distance (ft), measured from the curb ramp to the far curb or center of a pedestrian refuge island
• $S_{\text{walk}}$ = Standard pedestrian walking speed = $3.5\text{ ft/s}$ ($1.1\text{ m/s}$) (reduced to $3.0\text{ ft/s}$ in areas with significant elderly populations, school children, or persons with mobility impairments)

3. Bikeway Geometric Facility Selection & Protected Intersections

According to the FHWA Bikeway Selection Guide and AASHTO Guide for the Development of Bicycle Facilities, facility typology is selected based on motor vehicle operating speed and traffic volume (ADT):

                                FHWA BIKEWAY SELECTION MATRIX

   Speed (mph)
      ^
   50 |                                            SEPARATED / PROTECTED
   45 |                                            BIKE LANES
   40 |                      BUFFERED BIKE LANES   (Cycle Tracks / Sidepaths)
   35 |                      (5 ft lane + 3 ft buf)
   30 | --------------------------------------------------------------------
   25 | SHARED LANES
   20 | (Sharrows / Bike Blvd)
    0 +--------------------------------------------------------------------->
      0             1,500          3,000          6,000         10,000+   ADT

A. Bikeway Typologies:

1. Shared Lanes / Sharrows: Suitable only on low-speed ($V \le 25\text{ mph}$), low-volume ($\text{ADT} < 3,000\text{ vpd}$) residential streets or bicycle boulevards.
2. Conventional Bike Lanes: Minimum width $5.0\text{ ft}$ from curb face ($4.0\text{ ft}$ uncurbed).
3. Buffered Bike Lanes: Standard $5.0\text{ ft}$ lane plus a $2.0\text{ to }3.0\text{ ft}$ painted chevron buffer separating bikes from motor vehicles or on-street parking door zones.
4. Separated / Protected Bike Lanes (Cycle Tracks): Physical vertical separation (flex posts, concrete curb, bollards, on-street parking). Minimum one-way width is $6.5\text{ ft}$ (plus $3.0\text{ ft}$ buffer); two-way cycle tracks require $10.0\text{ to }12.0\text{ ft}$ width.

B. Protected Intersection ("Dutch Junction") Geometry:

At intersections, protected bike lanes maintain separation up to the crosswalk using four critical geometric elements:

• Corner Refuge Islands: Protect bicyclists from turning motor vehicles and slow turning vehicle speeds ($R_{\text{turn}} = 10\text{--}15\text{ ft}$).
• Setback Crossing ($6.0\text{ to }16.5\text{ ft}$): Bends the bike crossing away from the through street by $6.0\text{ to }16.5\text{ ft}$ ($2.0\text{ to }5.0\text{ m}$). This creates a $90^\circ$ driver visibility angle and provides space for a turning car to yield without blocking the through lane.
• Forward Bicycle Queue Box: Positions waiting cyclists ahead of queued motor vehicles.
• Pedestrian Cut-Throughs: Separates pedestrian crossings from bicycle paths.