11.3 Bicycle Accommodation & Detour Signing in TTC Zones

Bicycle Accommodation & Detour Signing in TTC Zones

Bicyclists have unique operational characteristics that make them particularly susceptible to work zone hazards. Unlike motor vehicles, bicycles rely on narrow rubber tires, balance, and human propulsion. Roadway surface irregularities, narrow lane widths, sudden lane shifts, loose gravel, and unannounced bikeway closures create severe safety risks. MUTCD Section 6N.04 establishes that bicyclists must be accommodated through TTC zones with the same care and planning as motor vehicle traffic and pedestrians.

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MUTCD & AASHTO Principles for Bicycle Accommodation

The 11th Edition Bicycle Typical Applications (TA-47 to TA-51)

The 11th Edition added five typical applications covering work that affects bicycle lanes and shared-use paths — none of which existed in the 2009 MUTCD. Table 6P-1 groups them under "Work in the Vicinity of Bicycle Lanes and Shared Use Paths (see Section 6N.04)":

TA-47 sets the speed thresholds that drive the accommodation decision: a shared lane is appropriate where the speed limit is 30 mph or less, and where a bicycle lane on a roadway posted 35 mph or higher is closed and conditions are not appropriate for a shared lane, a separate bicycle facility or detour route should be considered.

Under MUTCD Section 6N.04, bicyclists and pedestrians should not be exposed to unprotected excavations, open utility access, overhanging equipment, or other such conditions, nor should they be unexpectedly forced into hazardous mixing situations without advance warning. Work zone planners must evaluate the existing bicycle network and select an accommodation strategy based on a clear hierarchy of options.

Hierarchy of Bicycle Accommodation Strategies

+-----------------------------------------------------------------------+
|              BICYCLE ACCOMMODATION SELECTION HIERARCHY                 |
+-----------------------------------------------------------------------+
| 1. MAINTAIN EXISTING FACILITY: Keep bike lane open with full width    |
|    through the work zone using positive channelization.               |
|                                                                       |
| 2. PROVIDE TEMPORARY BYPASS: Construct temporary bike lane within     |
|    the right-of-way adjacent to motor vehicle travel lanes.           |
|                                                                       |
| 3. SHARED LANE OPERATION: Allow mixed traffic only if speeds are      |
|    low (<= 30 mph) and traffic volumes permit safe passing.            |
|                                                                       |
| 4. SIGNED BICYCLE DETOUR: Detour cyclists onto an alternate parallel  |
|    facility offering equal safety and minimal added distance.          |
+-----------------------------------------------------------------------+

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Temporary Bicycle Lane Design & Channelization

When a temporary bike lane is constructed through a work zone, geometric dimensions and device selections must accommodate bicyclist operating envelopes and prevent handlebar snags.

Width & Clearance Tolerances

• Minimum Lane Width: The standard clear width for a temporary bike lane is 5.0 feet (1.5 m). The absolute minimum width adjacent to a smooth curb or channelizing barrier is 4.0 feet (1.2 m) (excluding any gutter pan width).
• Handlebar Clearance Envelope: Bicyclists require a minimum operating width of 3.0 feet for balance, plus 1.0 foot of lateral clearance on each side to avoid striking barriers, sign posts, or channelizing drums with their handlebars.
• Lateral Buffer Space: Where motor vehicle travel speeds exceed 35 mph, a lateral buffer space of 2.0 to 3.0 feet separated by flexible delineator posts or low-profile barriers should separate the temporary bike lane from active traffic.
• Channelizing Devices: Longitudinal channelizing devices (LCDs) or low-profile barriers with smooth surfaces are preferred over standard traffic cones or tall drums, which can be knocked into the bike lane by vehicle wind shear or cause pedal strikes.

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Shared-Lane Accommodation & Advanced Warning Signing

In space-constrained urban corridors where right-of-way width cannot preserve a dedicated bike lane, bicyclists and motor vehicles must temporarily share a single travel lane.

Operating Conditions for Shared Lanes

Shared-lane accommodation is appropriate where the speed limit is 30 mph or less and traffic volumes allow drivers to safely follow or pass bicyclists. Where a bicycle lane on a roadway with a speed limit of 35 mph or higher is closed and conditions are not appropriate for a shared lane, a separate bicycle facility or detour route should be considered.

Required Warning Sign Assemblies

1. BICYCLISTS ALLOWED USE OF FULL LANE Sign (R9-20): Installed in advance of and throughout the shared section to inform drivers that bicyclists are legally permitted to occupy the center of the travel lane to avoid door zones or pinch points.
2. Bicycle Warning Sign (W11-1) with an IN ROAD / IN STREET plaque (W16-1P, W16-1aP): Placed in advance of the lane transition to alert motorists to expect bicyclists operating in the travel lane. The SHARE THE ROAD plaque was deleted in the 11th Edition because research showed road users did not understand it.
3. Temporary Sharrow Markings: Shared Lane Markings (sharrows) painted on the pavement outside the motor vehicle tire tracks to visually reinforce lane sharing.

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Bicycle Detour Route Design & Signing Standards

When a work zone completely closes a bike lane or shared-use path without room for an on-site bypass, a formal Bicycle Detour MUST be established.

Detour Route Selection Criteria

• Directness & Distance: Detours must minimize added travel distance (preferably adding no more than 0.25 to 0.5 miles to the trip).
• Facility Quality: The detour route should offer safety amenities comparable to the closed facility (e.g., detouring a protected bike path onto a high-speed multi-lane arterial without bike lanes is non-compliant).
• Intersection Controls: Intersections along the detour route must provide safe crossing controls, including bicycle-sensitive signal actuation (loops or pushbuttons) and clear sight lines.
• Topography: Avoid directing bicyclists up steep grades or across unpaved surfaces.

Bicycle Detour Signing Assemblies (MUTCD M4-9 Series)

   +-----------------------+
   |  PED/BIKE DETOUR      |  <-- M4-9a (Black legend on orange background)
   |          [-->]        |  <-- Integrated Directional Arrow
   +-----------------------+

• M4-9a (Pedestrian/Bicyclist Detour), M4-9b (Pedestrian Detour), M4-9c (Bicyclist Detour): Black legend and border on an orange background. Use M4-9a where a combined pedestrian/bicyclist detour has been established and M4-9c where only a bicyclist detour has been established. If used, the sign shall have an arrow pointing in the appropriate direction, either on the sign face or on a supplemental plaque.
• Placement Frequency: Detour assemblies MUST be placed at the point of closure, at every turn along the detour route, at intermediate intersections on long straight stretches, and where the detour rejoins the primary bicycle facility (using the END DETOUR (M4-8a) sign or the END (M4-8bP) plaque).

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Mitigation of Physical Roadway Surface Hazards

Bicyclists are vulnerable to small physical roadway defects that motor vehicles roll over without disruption. TTC inspectors must inspect work zone pavements daily for the following hazards:

1. Steel Trench Plates

• Anti-Skid Coating: Steel plates installed within bike lanes or shared lanes MUST be coated with a high-friction anti-skid surface material (such as epoxy aggregate) to prevent tire slipping under wet conditions.
• Beveled Edges: Plate edges parallel or perpendicular to bicycle travel must be tapered with asphalt cold-patch to a slope of 1:4 or flatter, ensuring the vertical lip does not exceed 0.25 inches (6.4 mm).
• Warning Signs: A STEEL PLATE AHEAD (W8-24) sign may be used in advance of trench plate locations to warn road users that the road surface might be uneven and might create slippery conditions during wet weather.

2. Longitudinal Slots, Joints, & Utility Trenches

• Pavement grooves, cold joints, or open utility trenches running parallel to bicycle travel can trap narrow bike tires, causing catastrophic forward-pitch falls. Any longitudinal gap or slot exceeding 0.5 inches (13 mm) in width MUST be filled flush with temporary asphalt or covered with anti-skid plates.

3. Bicycle-Safe Drain Grates

• Drainage grates with slots parallel to traffic flow trap bicycle front wheels. Non-compliant grates inside work zone detours must be replaced with bicycle-safe vane-grid grates or temporary steel mesh covers.

4. Debris & Loose Aggregate Control

• Asphalt milling operations leave loose stone chips and gravel on shoulders and bike lanes. Work zone maintenance plans must mandate daily mechanical sweeping along all bicycle travel paths.