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OCR for page 29
29 MUTCD guidance Work zone strategy Multilane Freeway Two-lane nonfreeway Alternating one-way operation NA NA At-grade intersections NA Detour Diversion Full road closure (1) (1) (1) Exhibit 4-3. Diversion typical section with normal Interchange ramp NA Intermittent closure crown. Lane closure Lane constriction (2) Median crossover NA Use of shoulder (3) 4.1.4 Roadside Design and Barrier Placement Explicitly addressed by MUTCD Part 6. For a discussion of the principles guiding roadside design NA Not applicable. 1 Full road closure requires a detour. and safety for construction work zones, see Chapter 5. For a 2 MUTCD typical application provided for one category of lane constriction specific discussion of barrier use for a temporary bridge that is (Shoulder Work with Minor Encroachment) pertains to minor roads with low speeds. part of a diversion on a two-lane, two-way highway, refer to 3 Covered in conjunction with Lane Shift. Section 5.5.4. Exhibit 4-1. Coverage of MUTCD Part 6 TTC guidance for various work zone strategies. 4.2 Lane Constriction General considerations are outlined in Section 3.1.7. It is desirable to maintain the approach road travel lane width 4.1.3 Cross Section and Surface through construction work zones. However, "lane constric- From a traffic operations and safety perspective, the diver- tion" implies a width reduction, and desirable dimensions are sion cross section should be the same as the approach road- generally not attainable. Therefore, this strategy inherently way. However, this expectation is often not reasonable or involves providing a design feature that is less than desirable. practical. The duration of service, traffic volume, vehicle mix, Research indicates that reducing lane widths though work construction cost, and impacts of the diversion are relevant zones may increase crash rates. Relationships between the considerations. Recommended two-lane diversion travel way magnitude of the reduction and the corresponding safety and roadway (i.e., combined traveled way and shoulder) effect were not reported. widths are shown in Exhibit 4-5. Values above those shown in It is common practice to reference "travel lane width" as the Exhibit 4-5, up to those used for permanent roads of the same key lane constriction decision variable. However, operations in functional class, provide desirable service, but the additional one travel lane are influenced by operations in adjacent lanes. cost is not necessarily justified. Additionally, adjoining travel lanes occasionally have different The Section 2.2.8 discussion on traveled way surface type is widths. Therefore, it may be more appropriate for design applicable to diversions. Shoulders are often unpaved. The guidance to address traveled way width. For example, a 3.0-m guidance in Section 2.2.8 applies to traveled way and shoulder [10-ft]-wide travel lane adjacent to a 3.6-m [12-ft] travel lane cross slopes. is generally more desirable than a 3.0-m [10-ft]-wide travel The pavement structure provided with higher-volume lane adjacent to a travel lane of the same width. diversions should reflect the difficulty of performing surface A number of factors should be considered in determining maintenance and repairs within a complex operational envi- the minimum acceptable traveled way width, including the ronment. For this condition, providing a highly durable pave- presence and proximity of roadside features. As indicated by ment structure should be considered. the Roadside Design Guide (see Section 5.6.1 of this report), Exhibit 4-2. Example plan of diversion.