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From page 188... ... 188 This chapter provides guidance on the use and installation of traffic control devices at a diverging diamond interchange (DDI) to inform, guide, and control various traffic modes such as motorists, pedestrians, and bicycles. Read the entire page →
From page 189... ... Traffic Control Devices and Illumination Applications 189 4. Information about other aspects of the interchange and surrounding area is provided mostly through signage. Read the entire page →
From page 190... ... 190 Diverging Diamond Interchange Informational Guide The combination "No Left Turn" and "No Right Turn" sign assembly at the crossover is consistently used at DDIs, as shown in Exhibit 7-2. The use of "No Left Turn" and "No Right Turn" signs at ramps has increased since the first DDIs opened in Missouri. Read the entire page →
From page 191... ... Traffic Control Devices and Illumination Applications 191 Exhibit 7-3. Overhead application of "No Left Turn" and "No Right Turn" signs. Read the entire page →
From page 192... ... 192 Diverging Diamond Interchange Informational Guide is used to direct drivers to the left side of the DDI; at the second crossover, the "Keep Right" sign is used to direct drivers back to the right side. A "Keep Right" sign may also be appropriate if the approaching roadway to the DDI is undivided and an island is added to create the DDI geometry. Read the entire page →
From page 193... ... Traffic Control Devices and Illumination Applications 193 These signs are shown in Exhibit 7-6. Exhibit 7-6 assumes ramp terminals are yield-controlled, but if they are signalized Advance Signal Ahead signs could be placed on the off-ramp. Read the entire page →
From page 194... ... 194 Diverging Diamond Interchange Informational Guide Exhibit 7-7. Typical guide sign sequence. Read the entire page →
From page 195... ... Traffic Control Devices and Illumination Applications 195 overhead where the crossroad passes under the freeway. The signs remind drivers about the lane assignments for merging onto the freeway, and in some cases, signage is provided for through movements as well. Read the entire page →
From page 196... ... 196 Diverging Diamond Interchange Informational Guide at the approach can discourage drivers from cutting across multiple lanes to obtain a faster path through the reverse curves of the intersection crossover. Lane line extensions can be helpful for directing turning and crossover vehicles. Read the entire page →
From page 197... ... Traffic Control Devices and Illumination Applications 197 7.4.3 Lane Use Arrows Lane use arrows, along with intersection lane control signs, provide the best opportunity to guide motorists correctly through the interchange. Standard lane use arrows should be used on each lane approaching each component intersection of the interchange, as these also provide a visual cue against wrong-way movements. Read the entire page →
From page 198... ... 198 Diverging Diamond Interchange Informational Guide 7.4.5 Pedestrian Crosswalk Markings Pedestrian crosswalk markings should be installed at all pedestrian crossing locations. Crosswalk markings provide guidance to pedestrians who are navigating a DDI while also providing a visual cue to drivers of where pedestrians may be present in the street. Read the entire page →
From page 199... ... Traffic Control Devices and Illumination Applications 199 used to provide additional guidance through intersections for motorized vehicles, similar bicycle lane line extensions should be used to provide similar additional guidance for bicyclists. 7.5 Signal Equipment While traffic signal design tends to come relatively late in the process of designing an interchange, there are a few critical issues that should be considered before the geometric design is complete. Read the entire page →
From page 200... ... 200 Diverging Diamond Interchange Informational Guide together will significantly increase the importance of perfectly synced progression, lessen the impact of long detection cables, and increase the visibility of both crossovers from one location. Crossovers that are spaced farther apart will likely result in platoon dispersion that will make tight synchronization less critical. Read the entire page →
From page 201... ... Traffic Control Devices and Illumination Applications 201 on where vehicles are currently located. If one controller is used to operate both crossovers, it may be difficult or impossible to see all movements. Read the entire page →
From page 202... ... 202 Diverging Diamond Interchange Informational Guide 7.5.3 Signal Poles and Displays The location of signal poles is another important step in the traffic signal design process. All signal head and pole installations must be in compliance with the MUTCD (1) Read the entire page →
From page 203... ... Traffic Control Devices and Illumination Applications 203 movement. Type 2 signal heads may help convey and confirm to drivers that they are not supposed to turn at the intersection (as seen in Exhibit 7-17) Read the entire page →
From page 204... ... 204 Diverging Diamond Interchange Informational Guide visibility effects for an outbound DDI movement approaching the crossover is shown in Exhibit 7-20 where the presence of multiple overhead mast arms and signal heads creates visual clutter and makes it difficult to identify the appropriate signal. 7.5.3.3 Supplemental Vehicle Signals Supplemental signal heads are recommended when the visibility of overhead-mounted signal heads is limited because of the horizontal curvature of the crossover or vertical alignment of the bridge structure. Read the entire page →
From page 205... ... Exhibit 7-20. Mast arm assembly limiting approach visibility (2) Read the entire page →
From page 206... ... 206 Diverging Diamond Interchange Informational Guide For the inbound movement, the supplemental signal head is typically installed on the right- hand side of the street as illustrated in Exhibit 7-21. For the outbound movement, the supplemental signal head is typically installed on the left-hand side of the street as illustrated in Exhibit 7-22. Read the entire page →
From page 207... ... Traffic Control Devices and Illumination Applications 207 An APS consists of a push button with a push-button locator tone to assist pedestrians who are visually impaired to find the device, as well as a tactile arrow and an audible message. The audible message communicates to the visually impaired traveler when the walk interval phase is active. Read the entire page →
From page 208... ... 208 Diverging Diamond Interchange Informational Guide [i.e., the push-button information message (see MUTCD 4E.13) Read the entire page →
From page 209... ... Traffic Control Devices and Illumination Applications 209 Where pedestrians need to travel through a channelized island to complete their crossing, clear guidance (such as a raised curb) is needed to help pedestrians navigate through the island to the next crossing point. Read the entire page →
From page 210... ... 210 Diverging Diamond Interchange Informational Guide operate as fully-actuated signals if desired. One benefit of installing detection at a DDI, even if the intention is to operate it as pre-timed, is that it allows for free operations in off-peak or late-night conditions and allows for flexibility in future operations. Read the entire page →
From page 211... ... Traffic Control Devices and Illumination Applications 211 details such as NCHRP Report 812: Signal Timing Manual, Second Edition (5) Read the entire page →
From page 212... ... 212 Diverging Diamond Interchange Informational Guide generally desirable to provide at least partial interchange lighting systems at rural DDI locations, but consideration should be given to complete interchange lighting designs. Complete interchange lighting will be desirable on bridge designs in urban and suburban areas. Read the entire page →
From page 213... ... Traffic Control Devices and Illumination Applications 213 ramps shows key merge and diverge points at the entry and exit ramps. Post-top lighting is used along the bridge for aesthetics. Read the entire page →
From page 214... ... 214 Diverging Diamond Interchange Informational Guide Exhibit 7-33. Recessed lighting in DDI center walkway (4) Read the entire page →

From page 188...

... 188 This chapter provides guidance on the use and installation of traffic control devices at a diverging diamond interchange (DDI) to inform, guide, and control various traffic modes such as motorists, pedestrians, and bicycles.