Work Zone - 6.04 Detours & Alternate Routes

6.04 Detours & Alternate Routes

The project designer should ensure that sign placement will fit the locations shown along the detour or alternate route and that signing will not conflict with existing signs, bridges, driveways, trees, landscaping, or pedestrian movements. Detours and alternate routes should be reviewed for upgrades to existing signing, pavement marking and traffic signals. Considerations must be given to the adequacy of shoulders, lane widths, turning radius for commercial vehicles (Auto-turn or turning template(s)), and structural condition of pavement. Timing may need to be adjusted on signals along the detour route.

Project designers must coordinate and document approval of detours and alternate routes with local transportation agencies and affected parties to avoid conflicts with local projects and transportation needs (email may serve as official documentation). In addition, a field review of the detour should take place to assess route conditions. Traffic volumes should also be observed. Anticipated modifications to existing traffic patterns should be noted during the field review.

All existing restrictions (horizontal, vertical, weight) must be evaluated on the proposed detour or alternate routes to ensure that traffic is not further impeded or restricted. Emergency services should be provided access to the worksite at all times for any emergency related event within or adjacent to the work zone. Project engineers should evaluate and discuss detour and alternate routes with emergency service providers (fire, police, ambulances, etc.) so that response times may be reviewed and taken into account. Contractors are required to include emergency access plans as part of the WZTCP and coordinate with the emergency service providers.

Consideration must be given to detour routes that cross railroad crossings at grade. An increase in traffic volumes on the detour route may require the use of gates at the crossing. The WZMU should be contacted when a detour route includes an at-grade crossing to determine the necessary traffic control.

6.04.01 Full Road Closures

Full road closures are the most positive separation of road users and workers. They must be evaluated and considered for projects with underground utility work, bridge demo, deck replacements, and complete reconstruction activities. Consider expedited work schedules to complete the work and return the road to the user as quickly as possible. Road closures also impact travel time as there may not be reasonable detour routes around the project site.

Detour routes for a full closure must also be reviewed for capacity, existing crash patterns, and signal timing that could contribute to additional crashes and delay.

In advance of a closure, lighted Type III barricades must be placed on the shoulder or behind curb at the nearest cross road in advance of the closure. R11-3 signing must be placed above and behind the Type III barricades.

At a road closure point, lighted Type III barricades must be placed across the entire closed area. R11-2 or other R11 series signs must be placed on or above and behind the Type III barricade in the center of the closure. Refer to MMUTCD Part 6 (Sections 6F.08- 09 and Figure 6F-3).

Areas that warrant additional protection from a hazard, or if traffic is found to be moving signs, the special provision for Temporary Water Filled Base Sign System - 12RC812-A445 may be utilized.

6.04.02 Directional Detours

Directional detours provide additional work space for part width construction. It is recommended that these types of closures are evaluated in the same manner as complete roadway closures where a specific direction of travel may need to be detoured. Projects must be reviewed carefully to determine which direction of travel should be detoured. Impacts on road user travel and their ability to change their travel path must be Included in the review.

For non-freeway projects, it is recommended to detour traffic the same direction for the duration of the project. This provides motorists with consistent routes and travel paths as changing back and forth could lead to head-on traffic crashes. Consistency is critical for areas that have residential or business driveway access.

In business or residential areas, public feedback may be helpful in determining which direction to detour. Public input should be taken into consideration but engineering judgment should be utilized when making the final MOT selection.

Turning movements and existing capacity of the detour route, along with public input, should be a factor in the design. A detour route that has all right hand turns and free flow movements would be desirable over left hand turns.

Freeway projects have controlled access points so the need to maintain the same direction of traffic for the duration is not as critical for non-freeways. The traffic volumes and viable detour routes should be considered when determining which direction to maintain during the course of the project.

6.04.03 Ramp Closures

Ramp closures can provide separation of road users and workers and also reduce the amount of interaction between mainline traffic and entering traffic. Ramp closures should be evaluated when construction is occurring at or near the merge point and when merging locations will require a stop condition or visibility is impacted. These locations are known to contribute to congestion, backups, and rear end and side swipe crashes. Closing ramps may improve the safety and travel time of mainline traffic.

Design considerations should include requirements to prevent the closure of adjacent interchanges simultaneously. Consideration should be given to expedited work schedules to complete the work and return the ramp to the user as quickly as possible.

6.04.04 Detour Signing

The type and location of detour signing depends on the following factors:

• ADT
• Area traffic generators (i.e. commercial or institutional land uses nearby residential areas and transit stops).
• Time of year
• Project duration
• Other consideration: emergency operations, incidents, planned special events, etc.

Detour signing must be placed as described in the MMUTCD Part 6 (Sections 6F.19, 6F.20, 6F.28, and 6F.59). Guidance for freeway, ramps, non-freeway and local roads are summarized in Tables 6-8 and 6-9.

Cardinal directional signs (North, South, East, West) are required if both directions of the roadway are closed and detoured. If the detour route combines both directions, the cardinal direction sign may be eliminated. Detour signs posted on non-freeway routes at left turns should be posted at the near right and far left of the intersection. On freeways, one-way, and/or divided roadways, detour signs should be placed on both sides of the roadway in the same direction.

When signing for a detour ahead or road closure ahead, adding a supplemental plaque is required when the sign is not on the roadway to be closed or detoured. A route marker should be used or the road name can be spelled out if space allows as shown in Exhibits 6-29 and 6-30.

Exhibit 6-29: Detour with Road Name

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Exhibit 6-30: Detour with Route Marker

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A. Sign Color and Sizes

Detour sign color is based on the parent route marker sign. The local road name must not extend past the edges of the M4-9 sign by more than 3 inches on either side. The letter size of the sign may need to be reduced to fit within these dimensions. If the road name consists of two words, they may be placed on two separate lines. For detour signs designed with route marker signs, use the standard sizes and colors as described in the Work Zone SHS Manual (SHS 13-Work Zone) found on the MDOT Traffic Signing page.

The M4-8 “DETOUR” plaque must be used on top of all state route detours with the route marker designation. The M4-8 sign is always on an orange background with black letters. Additional information regarding route markers can be found in MMUTCD Part 2.

Exhibit 6-31: Detour Clusters

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The addition of special sign designs may be appropriate for some projects to enhance the standard detour signing. These signs have an orange background with a black border and should include the route marker signs and arrows. The word “DETOUR” is not required for these signs as they are recognized as a construction detour sign.

Exhibit 6-32: Sample Detour Signs

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B. End Detour

END DETOUR (M4-8a) signs are recommended to end a detour route. If the detour is for a local route, the road name plaque must be placed above the M4-8a sign. If the detour route is a numbered route, the cardinal direction and the route plaque (if appropriate) is required below the M4-8a sign as detailed in Exhibit 6-31.

C. Portable Changeable Message Signs (PCMS)

Example: PCMS may be used for detours less than 72 hours in lieu of detour signing as determined by the Engineer.

Phase 1: EXIT XXX CLOSED AHEAD
Phase 2: USE EXIT XXX
OR
Phase 1: EXIT XXX CLOSED AHEAD
Phase 2: FRIDAY 9 PM - 10AM AM SATURDAY

Additional information regarding PCMS placement and messaging is provided in Appendix F and in the MMUTCD Part 6 (Section 6F.60).

Table 6-5:Non-Trunkline Detour Signing Design Guidelines

*all road name signs to be paid for as Sign Type B Special

Detour Duration	Non-Trunkline Detour
	Signing	Example*
< 24 hours	M4-9 (R)(L) - Detour Sign with appropriate directional arrow at each decision point. Or portable changeable message boards (6.04.04 Section C).
24 - 72 hours	M4-9 (R)(L) - Detour Sign with Road Name Plaque and appropriate directional arrow at each decision point. Or portable changeable message boards (6.04.04 Section C).
> 72 hours	M4-9 (R)(L)(U) - Detour Sign with Road Name Plaque and appropriate directional arrow at each decision point near right and far left corners of the intersection. M4-9 (UL)(UR) - to be placed in advance of each turn. An "up" pull through arrow should be required after each major intersection, and should be considered after each turn decision point

Table 6-6: Trunkline Detour Design Signing Guidelines

Detour Duration	Trunkline Detour
	Signing	Example
< 72 hours	M4-8 Detour Plaque M3-1, M3-2, M3-3, M3-4 Cardinal Directional Sign M1-1, M1-2, M1-3, M1-4, M1-6 Route Marker Sign M6-1(R)(L), M6-2(R)(L) Directional arrow at each turn or exit A PCMS may be used for simple detours (6.04.04 Section C)	test
> 72 hours	M4-8 Detour Plaque M3-1, M3-2, M3-3, M3-4 Cardinal Directional Sign M1-1, M1-2, M1-3, M1-4, M1-6 Route Marker Sign with directional plaque must be placed in advance and at each turn M5-1, M5-2, M5-3, M6-1, M6-2, M6-3 Directional Arrow at each turn or exit An "up" pull through arrow is recommended after each major interchange and after each turn or exit

Table 6-7: Detour Signing Placement Guidelines

Detour Signing Placement Guidelines
Roadway	Turning Detour Signing	Advance Turn Detour Signing	Pull Thru Detour Arrow Signing
Non-Freeway	50 feet (min) before intersection spring point	500 feet (min) before intersection spring point	500 feet (max) after intersection
Freeway	100 feet (min) before exit lane taper	½ Mile (min) before exit lane taper	500 feet (max) after lane merge taper
Ramps	50 feet (min) before spring point	500 feet (min) before spring point	N/A

Categories

• Chapter 6: Traffic Control Devices and Implementation
• Work Zone Safety and Mobility Manual Index