Design and Access Management Guidelines for Truck Routes: Planning and Design Guide (2020) / Chapter Skim
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29 4.1 Introduction Chapter 4 addresses geometric design and access management to accommodate trucks. With the exception of some industrial and port locations, where the traffic stream may consist almost exclusively of trucks, very few roadway segments and intersections are designed solely to serve trucks.
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Design Vehicle Type Symbol Dimensions (ft) Overall Overhang WB1 WB2 S T WB3 WB4 Typical Kingpin to Center of Rear Tandem AxleHeight Width Length Front Rear Single-Unit Trucks Single-Unit Truck SU-30 11.0–13.5 8.0 30.0 4.0 6.0 20.0 -- -- -- -- -- -- Single-Unit Truck (three axle)
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Geometric Design and Access Management to Accommodate Trucks 31 summary of the characteristics of these truck design vehicles. The overall length of a truck is the distance from the front to the rear of the vehicle not including appurtenances, such as loading/ unloading devices, resilient bumpers, or aerodynamic devices.
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32 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide Truck count data, gathered as part of the transportation planning process, can assist agencies in the selection of appropriate design vehicles for particular projects or corridors. The FHWA Traffic Monitoring Guide (FHWA 2016)
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Geometric Design and Access Management to Accommodate Trucks 33 retail businesses throughout the United States get their deliveries from WB-67 trucks, although WB-62 trucks or WB-67 trucks with the rear axles pulled forward for a 40- or 41-ft KPRA distance may be used in some states. As for the smaller semitrailer design vehicles, WB-40 trucks are specialized vehicles used in transporting some freight containers, while WB-62 trucks with 48-ft trailers have largely been replaced by WB-67 trucks.
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34 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide known as the swept path width. Figure 9 illustrates offtracking and swept path width.
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Geometric Design and Access Management to Accommodate Trucks 35 reason, turning templates are said to illustrate low-speed offtracking. Turning templates are needed because offtracking and swept path width are not constant throughout a truck-turning maneuver.
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36 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide Figure 10. Dimensions and minimum turning path for the Interstate semitrailer (WB-67)
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Geometric Design and Access Management to Accommodate Trucks 37 Figure 11 shows that, where parking lanes or other features, such as curb extensions are present, there is an effective radius for right-turn maneuvers that is larger than the actual curb return radius. Turning templates for specific design vehicles, or the software equivalent of such templates, are also used to assess median opening designs.
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38 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide • Where the volume of turning movements by large trucks is so high that interference with traffic operations would be more than occasional, rerouting truck traffic may be appropriate. Rerouting of trucks needs to be considered in consultation with the local community.
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Geometric Design and Access Management to Accommodate Trucks 39 locations to minimize the potential for truck encroachment on the curbline. This may be effective in minimizing truck encroachment but, where pedestrians are present, it increases the pedestrian crossing distance by the width of the shoulder provided.
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40 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide Figure 13. Turning requirements for specific design vehicles (adapted from City of Portland, Oregon, 2008)
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Geometric Design and Access Management to Accommodate Trucks 41 4.3.2 Median End Treatments Median openings on divided highways at intersection and nonintersection locations are typically designed in accordance with guidance in Chapter 9 of the Green Book. The vehicle paths through the median opening for left-turning vehicles are typically laid out with turning template software, as discussed in Section 4.2.3 of this Guide.
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42 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide and median openings. Left-turn lanes provide both traffic operational and safety benefits.
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Geometric Design and Access Management to Accommodate Trucks 43 Deciding Where to Install a Left-Turn Lane The decision to install a left-turn lane at a particular location depends on a number of factors, including overall traffic volume, left-turn volume, and operating speed. Many transportation agencies have adopted their own left-turn lane recommendations and warrants based on one of the following references: • Harmelink warrants (Harmelink 1967)
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44 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide identify the additional need to consider the volume (or percentage) of large vehicles and their extra vehicle length in estimating the storage length for left-turn lanes.
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Geometric Design and Access Management to Accommodate Trucks 45 provides guidance concerning the appropriate offset distance for opposing left-turn lanes (Fitzpatrick et al.
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46 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide (a) Double Left-Turn Lanes (b)
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Geometric Design and Access Management to Accommodate Trucks 47 Figure 19. Trucks in staggered position preparing to turn left in a double left-turn lane.
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48 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide Safety Benefits of Right-Turn Lanes Removing right-turning vehicles from the through-traffic stream provides safety benefits as well, by reducing the potential for rear-end collisions in which through vehicles strike the rear of right-turning vehicles. Table 5 provides crash modification factors for right-turn lanes, as presented in the AASHTO Highway Safety Manual (HSM)
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Geometric Design and Access Management to Accommodate Trucks 49 Double and Triple Right-Turn Lanes Turning maneuvers are one of the key challenges faced by trucks on urban and suburban arterials, and some transportation agencies have indicated that right turns at intersections are most problematic for trucks. Double right-turn lanes not only increase the capacity of right-turn movements, but the outside (left)
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50 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide 4.3.5 Channelized Right-Turn Roadways Right-turn maneuvers at intersections are a key challenge faced by trucks on urban and suburban arterials because of the potential for trucks to either encroach into the adjacent lane or mount the curb to negotiate a right turn. Channelized right-turn roadways can provide a larger curb return radius to accommodate turning vehicles, including large trucks, without unnecessarily increasing the intersection pavement area and the pedestrian crossing distance.
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Geometric Design and Access Management to Accommodate Trucks 51 4.3.6 Indirect Left-Turn Movements Certain intersection designs remove direct left-turn paths and route left-turning traffic indirectly. Where medians are installed in the roadway to prevent direct left-turn movements, alternative routes should be provided to complete left-turn maneuvers.
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52 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide roadway followed by a U-turn (Path B in Figure 25)
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Geometric Design and Access Management to Accommodate Trucks 53 The following guidelines should be used when considering the design and placement of the loon: • At U-turn roadways where trucks are present, provide loons where needed to accommodate truck-turning paths in completing a U-turn maneuver. • Use turning templates in CADD software to ensure adequate design is provided for the design vehicle making a U-turn.
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54 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide Case Study: Selected Use of Loons at U-Turn Locations Along a Truck Route Michigan DOT (MDOT) makes extensive use of the MUT design in which all left turns are prohibited at the main intersections where two streets cross and left turns are accomplished indirectly by means of median U-turn roadways ("crossovers")
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Geometric Design and Access Management to Accommodate Trucks 55 The following guidelines should be used when considering jughandles for truck accommodation: • For left-turn movements with high truck demand, use of farside jughandles is recommended. • On corridors where left turns are prohibited, jughandles can work well for providing U-turns.
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56 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide Jughandles are not ideal on facilities that accommodate pedestrians, because they provide an additional roadway that pedestrians must cross. If possible, it is best to provide pedestrian and bicycle facilities on parallel streets to eliminate conflicts between jughandle traffic and nonmotorists.
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Geometric Design and Access Management to Accommodate Trucks 57 delay. Crosswalk lengths may also be shorter at quadrant intersections because there are no left-turn lanes at the main intersection.
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58 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide Case Study: Alternative Paths for Passenger Cars and Trucks MDOT uses some diamond interchanges with slip ramps to continuous frontage roads, similar to the interchange design that is also used commonly in Texas. At one location, MDOT found that the space between the crossroad ramp terminals was sufficient to store passenger cars making a direct left turn from one frontage road, but that large trucks turning left could not be stored in the space between the crossroad ramp terminals.
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Geometric Design and Access Management to Accommodate Trucks 59 Case Study: Replacement of Closely Spaced Signalized Intersections with Roundabouts on Arterial Corridor A heavily traveled arterial corridor in Louisiana, with high truck volumes, experienced traffic operational and safety issues because of a series of closely spaced signalized and unsignalized intersections and driveways in the vicinity of an Interstate interchange. The high volumes of trucks, midblock left-turn movements, and closely spaced driveways and intersections contributed to congestion along the corridor.
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60 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide Research has shown that roundabouts can provide a reduction of 48% in all crashes and 78% in injury crashes where a signalized intersection is converted to a roundabout, and a reduction of 44% for all crashes and 82% in injury crashes where an intersection with minor-road Stop-control is converted to a roundabout (AASHTO 2010)
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Geometric Design and Access Management to Accommodate Trucks 61 At single-lane and multilane roundabouts, transportation agencies often use a traversable apron around the perimeter of the central island to provide the additional width needed to accommodate the swept path width of large vehicles. Initially, truck drivers did not like using these raised aprons because of concerns with truck rollover and tire blowouts.
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62 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide Figure 32. Basic geometric elements of a roundabout (AASHTO 2018)
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Geometric Design and Access Management to Accommodate Trucks 63 Figure 33. Single-semitrailer truck using apron that surrounds the central island of a roundabout.
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64 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide In some cases, roundabouts have been designed with aprons or gated roadways through the central island to accommodate oversize trucks and emergency vehicles (see further discussion in Section 3.6 on OSOW permits for trucks)
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Geometric Design and Access Management to Accommodate Trucks 65 4.4.1 Conventional Diamond Interchanges and Closely Related Interchange Configurations A conventional diamond interchange consists of four diagonal ramps, two exit ramps and two entrance ramps on either side of a freeway, that connect the freeway to an arterial crossroad. Figure 36 illustrates a typical conventional diamond interchange.
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66 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide Key truck considerations in the design of conventional diamond interchanges include the following: • Design of the ramp terminals to accommodate left and right turns by trucks (see Section 4.2 on design vehicles)
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Geometric Design and Access Management to Accommodate Trucks 67 beyond the crossroad or both, thus minimizing the volume of left-turn movements that use the crossroad and the storage space needed between the ramp terminals on the crossroad. The same key design and truck considerations that apply to conventional diamond interchanges also apply to tight diamond interchanges and "folded diamond" interchanges (also known as partial cloverleaf interchanges)
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68 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide 4.4.2 Single-Point Diamond Interchanges SPDIs sometimes referred to as single-point urban interchanges (SPUIs) or just as singlepoint interchanges, are a modified form of a diamond interchange where opposing left turns from the ramps can flow simultaneously.
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Geometric Design and Access Management to Accommodate Trucks 69 4.4.3 Full Cloverleaf Interchanges A typical full cloverleaf interchange is illustrated in Figure 41. In this interchange configuration, all of the crossroad ramp terminals have free-flow operation, rather than Stop signs or traffic signals.
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70 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide of a conventional diamond ramp terminal. Figure 42 shows a basic plan view of the traffic flows at a DDI.
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Geometric Design and Access Management to Accommodate Trucks 71 a good resource for design alternatives to accommodate pedestrians and bicyclists as well as transit and heavy vehicles at a DDI. 4.4.5 Roundabout Interchanges Roundabout interchanges are interchanges with roundabouts, rather than with signalized or Stop-controlled intersections at the ramp terminals, as illustrated in Figure 44.
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72 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide Figure 44. Typical roundabout interchange.
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Geometric Design and Access Management to Accommodate Trucks 73 prevent wrong-way movements onto the freeway. Because U-turns at interchanges with teardrop-shaped roundabouts require navigating two roundabouts, these interchanges are preferable where minimal U-turns are expected.
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74 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide driveways within the development. Gattis et al.
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Geometric Design and Access Management to Accommodate Trucks 75 An abrupt end to a curb is undesirable because it is likely to snag a vehicle tire. The vertical face of a return curb provides entry-edge definition for an approaching motorist.
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76 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide may need to be provided within the island to deal with large trucks overrunning the island (Gattis et al.
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Geometric Design and Access Management to Accommodate Trucks 77 4.5.9 Combining Driveways A common access management solution is combining multiple driveways to reduce the number of driveways and the driveway density along a corridor and to minimize the conflicts between turning vehicles and through traffic. Combining driveways to a single commercial business establishment makes sense when three or more driveways or a continuous driveway frontage are provided.
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78 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide 4.5.12 Pedestrian and Bicycle Considerations Every driveway creates a potential for conflicts between motor vehicles, pedestrians, and bicyclists. Driveways are crossed by pedestrians on sidewalks, and bicyclists cross the paths of vehicles entering and leaving driveways.
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U.S. Customary Radius of Curve (ft)
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U.S. Customary Radius of Curve (ft)
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Geometric Design and Access Management to Accommodate Trucks 81 divided equally on either side of the centerline. In the latter method, extension of the outer edge tangent avoids a slight reverse curve on the outer edge.
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82 Design and Access Management Guidelines for Truck Routes: Planning and Design Guide to be retained, where permitted by local statute, although such reduced clearances are undesirable on truck routes. 4.6.6 Turnouts for Law Enforcement Activities Where paved shoulders wider than 8.5 ft are not provided on truck routes, it may be desirable for transportation agencies to provide paved turnouts, at intervals, so that trucks can stop outside the traveled way for law enforcement activities.
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Geometric Design and Access Management to Accommodate Trucks 83 4.10 Bicycle Facilities In the multimodal planning process, it may be desirable, where practical, to locate truck routes and bicycle facilities on different roads or streets within a corridor. Where bicycle facilities are provided along a truck route, the bicycle facilities should be designed to minimize conflicts between bicycles and trucks or other vehicles.
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