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51 Case Examples This chapter presents case examples of alternative intersection design and selection for six states (Figure 44): Alabama, Georgia, Indiana, Minnesota, Missouri, and Texas. In consul- tation with the topic panel, the following criteria were considered as a basis for choosing the Departments of Transportation (DOTs) for the case examples: ⢠Successfully implemented various types of alternative intersections; ⢠Established policies or guidelines for evaluation and selection of intersection types; ⢠Performed studies to assess operational, safety, and/or cost benefits of alternative intersections; ⢠Developed customized tools for evaluating intersection types; ⢠Developed effective materials for public outreach; ⢠Particularly unique implementation of alternative intersections; ⢠Diverse candidates for being the first type of alternative intersection in the region or nation versus implementation of an alternative intersection already known in the region or nation; ⢠Different methods for alternative intersection evaluation and selection (e.g., ICE policy versus less formal analysis methods); ⢠Level of detail provided in the survey comments; ⢠Some preference given for states with topic panel members; and ⢠Willingness to participate in a case example (18 DOTs). Geographic diversity was not prioritized as a selection criterion for the case examples. Table 20 lists the states selected for the case examples along with their method for selection of alternative intersections, basis for selection as a case example, and type of project highlighted in the case example. The case examples were developed based on phone interviews with personnel from the six states. Some of the alternative intersection topics covered during the interviews include the following: ⢠General approach and experience; ⢠Policies and standards; ⢠Performance; ⢠Unique forms of alternative intersections (e.g., hybrids); ⢠Considerations such as operations, safety, bicyclists and pedestrians, and constructability; ⢠Challenges to implementation and strategies to overcome those challenges; and ⢠Project examples. The case examples are described in the following sections of this chapter. C H A P T E R 4
52 Alternative Intersection Design and Selection State Method Used for Selection of Alternative Intersections Basis for Selection as Case Example Project Highlight Alabama Project by project Emerging use of alternative intersections In process of developing ICE policy Superstreet (signalized) Georgia ICE Customized ICE tool Agency team for alternative intersections Panel member state Roundabout Indiana ICE Intersection Decision Guide (IDG) Hybrid forms of alternative intersections Panel member state DDI Minnesota ICE Many existing roundabouts, superstreets, and DDIs Evaluation studies and design guidance for alternative intersections Superstreet (unsignalized) Missouri Project by project First state to implement DDI Unique forms of alternative intersections Evaluation studies and design guidance for alternative intersections Displaced left-turn interchange Texas Project by project Wide range of alternative intersection types open and operational Several existing CFIs Panel member state CFI Table 20. Overview of case examples. (Map created with mapchart.net ©) Figure 44. Map showing states selected for case examples.
Case Examples 53 Alabama General Approach to Alternative Intersections Alabama began implementing alternative intersections after seeing them successfully implemented in other states such as Georgia. In addition, stakeholders also gained experi- ence from using alternative intersections in other states, which helped Alabama overcome initial public resistance. Alabama found that alternative intersections were the best solutions in some cases and thus began proceeding with alternative intersection projects. Alabama is currently in the process of developing an Intersection Control Evaluation (ICE) policy and an evaluation tool to support implementation of the ICE policy. The tool is being tested on a pilot project to analyze several different intersections. The anticipated release date of the ICE policy and the tool is late 2020. Alabama was encouraged to develop an ICE policy after seeing a presentation from Georgia and meeting with the FHWA. Alabama developed its own roundabout guide (Jones and Majeed 2015) and has used different tools such as Capacity Analysis for Planning of Junctions (CAP-X) (Jenior, Haas, Butsick, and Ray 2018b) and the Georgia ICE tool (Georgia DOT 2018b) in its analysis of alternative intersections. Alabama is working toward expanding its use of alternative intersections in the future. Experiences with Alternative Intersections Alabama currently has superstreet intersections, median U-turn (MUT) intersections, and continuous green-T (CGT) intersections in operation. Alabama has found alternative inter sections to be a cost-effective solution to increasing capacity and improving safety and believes that its existing alternative intersections are performing well. The superstreet and MUT intersections have been effective at reducing various types of crashes, especially right- angle crashes. Alabama has the following alternative intersection types currently in the design or planning stages: CGT, diverging diamond interchange (DDI), MUT, single point diamond interchange (SPDI), and superstreet. Construction of Alabamaâs first roundabout on the state system, located at SR 5 and Bibb County Road 58 in Brent, Alabama, was completed in 2019. Alabamaâs first DDI, located at I-10 and SR-181 in Spanish Fort, Alabama, is currently under construction, with an anticipated completion date of spring 2020. A DDI was found to be the best fit for the turning movements at this location. Pedestrian accommodations at the DDI are being provided in the median. Challenges to Implementation Alabama has encountered some public opposition to alternative intersections. Specific concerns include additional travel time for re-routing of left-turn movements and access to businesses. Alabama has found that proactively meeting with businesses, local municipalities, and Emergency Medical Services helps to address concerns from stakeholders. For public outreach, Alabama developed websites for alternative intersection projects such as the DDI at I-10 and SR-181 (Alabama DOT n.d.a) and superstreets on SR-182 in Orange Beach (Alabama DOT n.d.b) and on US-280 in Birmingham (Alabama DOT 2013, Alabama n.d.c). The website for the DDI at I-10 and SR-181 includes a video on how to navigate a DDI. A conceptual drawing from Alabamaâs DDI brochure is shown in Figure 45. Alabama has also encountered challenges with signage for MUTs and superstreets and would like to see additional guidance developed for signage on these types of intersections.
54 Alternative Intersection Design and Selection Project Highlight: SR-182 Superstreet in Orange Beach, Alabama A 2-mile section of SR-182 in Orange Beach, Alabama, was converted from a five-lane section to a superstreet, and construction for the project was completed in 2018. The pre- vious five-lane section experienced 224 crashes between 2012 and 2014, and the corridor includes frequent driveways and side streets (Alabama DOT n.d.b). The project goals included increasing safety, reducing congestion, and improving the corridor aesthetics. The super- street with signalized U-turns was determined to be the best solution to balance mobility, safety, and access with limited right-of-way. Figure 46 shows a rendering of the intersection of the U-turn located east of the SR-182 and SR-161 intersection. Construction of the project was phased to accommodate peak traffic from tourism in the spring and summer. Modifica- tions to the signing, such as the addition of no-left-turn signs at driveways, were required because of the heavy presence of tourists who were unfamiliar with the area. Alabama also numbered the signals on SR-182 in an effort to improve wayfinding. Since completion of the project, Alabama believes that public perception has improved because of the reductions in congestion and traffic. (Alabama DOT n.d.a) Figure 45. Conceptual drawing of DDI from Alabamaâs public outreach brochure. (Alabama DOT n.d.b) Figure 46. Rendering of the U-turn east of the intersection of SR-182 and SR-161 in Orange Beach, Alabama.
Case Examples 55 Georgia General Approach to Alternative Intersections Georgia developed an ICE policy (Georgia DOT 2017), which took effect on July 1, 2017. Georgia developed the ICE policy in collaboration with FHWA after attending a peer exchange. Georgiaâs ICE policy includes a two-stage process with initial screening followed by alternative selection. An ICE is required for any intersection improvements that either (1) include roadways on the state system or National Highway System or (2) utilize state or fed- eral funds. Georgia has found that ICE allows the infusion of safety improvements into its entire construction work program and helps to encourage consideration of alternative intersections, as it requires practitioners to justify their decision. To implement its ICE policy, Georgia developed its own ICE spreadsheet tool (Georgia DOT 2018b). The tool analyzes operational and safety impacts and also provides benefit/cost analyses. In addition, the tool helps document other considerations such as environmental and public involvement concerns. The safety analysis is primarily based on the Crash Modification Factors (CMFs) in the CMF clearinghouse (FHWA 2019a). If a CMF is not available in the CMF clearinghouse, Georgia will sometimes use CMFs from FHWA tech briefs or other studies. In Georgiaâs experience, its ICE tool is effective at simplifying the ICE process, standardizing documentation, and reducing the amount of time required for the analysis. Georgiaâs design manual (Georgia DOT 2018a) includes a chapter on roundabouts, and Georgia also developed its own roundabout analysis tool (Georgia DOT 2019). Georgia also pro- vides guidance for signings and markings for roundabouts and superstreets (Georgia DOT 2018c). Georgia uses the term reduced conflict U-turn for its superstreets. Georgia is developing its own roundabout guide and is considering creating its own alternative intersection guide in the future. Georgia provides support for alternative intersections through its Roundabout and Alterna- tive Intersection Design team (RAID), which is housed in its office of traffic operations. The RAID performs reviews of designs and analyses for alternative intersections. In addition, the RAID sometimes undertakes the analysis or design of roundabouts for district traffic offices. Georgia also utilizes an on-call consultant contract to perform reviews, analyses, and design of roundabouts. Experiences with Alternative Intersections Georgia has a variety of alternative intersection types that are open and operational and is generally satisfied with their operational and safety performance. The first roundabout in Georgia was constructed in 1999. As of 2019, there are approximately 231 roundabouts in Georgia (including 10 mini roundabouts) with 46 of these roundabouts located on state routes. Georgia has found good crash reductions at roundabouts and is currently conduct- ing in-service reviews of several of its roundabouts. Georgia has six or seven DDIs open and operational and had pursued the DDI after staff toured the first DDI in Springfield, Missouri. Georgia also has approximately 38 superstreet intersections open and operational on the state route system. Georgia has pulled some before-and-after crash data for its superstreets, but a formal analysis has not yet been undertaken. One continuous flow intersection (CFI) is opera- tional in Georgia, which opened to traffic in 2017 (Figure 47), and a hybrid of a CFI and quad- rant roadway intersection (QRI) was under construction in Snellville, Georgia, in 2019. Georgia also has seven CGTs (four signalized, three unsignalized) and some SPDIs that are open and operational. In addition, several intersection types are in the planning or project development stages, especially roundabouts, with more than 50 roundabout projects in development. A concept for a displaced left-turn interchange is under development in Augusta, Georgia.
56 Alternative Intersection Design and Selection Challenges to Implementation Much of the public resistance encountered in Georgia centers around unfamiliarity, the re-routing of traffic, and changes in traffic behavior. DDI projects were often initiated from local agencies, and thus they garnered more initial public support. Georgia often holds open houses for roundabout projects. In Georgiaâs experience, public acceptance of roundabouts increases dramatically after the project is constructed. Other challenges encountered by Georgia in implementing roundabouts include the following: ⢠Pedestrian path is not well defined, ⢠Pouring the truck apron under traffic often requires a detour or asphalt widening, ⢠Providing lighting, and ⢠Grading the circle to drain away from the center island in all scenarios may adversely affect project cost (specifically, grading and staging), especially at locations where the roundabout intersection is located on a vertical grade. In the future, Georgia would like to see continued growth for the use and support of alter- native intersections along with greater proficiency by designers and contractors. Georgia has identified study needs related to alternative intersections that include a need for greater public education on alternative intersections, ways to make design and construction more efficient and cost-effective, comparisons of different roundabout types (e.g., mini, single-lane, multi-lane), more information on less-common intersection types, and information on alternative inter- section locations in the United States. Project Highlight: SR 41 at SR 18 in Meriwether County, Georgia (Roundabout) Georgia used quick response/maintenance funds to convert the two-way stop-controlled (TWSC) intersection at SR 41 and SR 18 in Meriwether County to a roundabout (Figure 48). The roundabout, which was opened to traffic in 2015 at an approximate cost of $240,000, was chosen over a multiway stop-controlled intersection, because it provided operational efficiencies while allowing for speed reduction and thus mitigating high-speed crashes. The intersection (Aerial drone footage, Courtesy Georgia DOT) Figure 47. Screenshot from drone video footage of CFI at SR 400 and SR 53 in Dawsonville, Georgia.
Case Examples 57 did not meet signal warrants because of low traffic volumes on all approaches. A draft in- service review of the roundabout by Georgia found that all legs are performing at level of service A (LOS A), along with the following crash reductions: 84% (total crashes), 77% (injury crashes), and 100% (fatal crashes). Project Highlight: SR 154 at Cedar Grove Road in South Fulton, Georgia (Roundabout) The five-leg TWSC intersection at SR 154 and Cedar Grove Road in South Fulton, Georgia, was converted to a four-leg roundabout (Figure 49) as part of Georgiaâs safety program. The roundabout was opened to traffic in 2014 with a total project cost of approximately $4.2 million. (Aerial drone footage, Courtesy Georgia DOT) Figure 48. Roundabout at SR 41 and SR 18 in Meriwether County, Georgia. (Aerial drone footage, Courtesy Georgia DOT) Figure 49. Roundabout at SR 154 and Cedar Grove Road in South Fulton, Georgia.
58 Alternative Intersection Design and Selection The scope of the project included relocation of the intersection, installation of a cul-de-sac, culvert extension, and concrete side barrier wall. Two other alternatives were considered: widening SR 154 and moving the intersection to the north as a TWSC intersection while removing the fifth leg. Signal warrants for the intersection were not met. The roundabout was selected as the preferred alternative because the widening alternative did not improve sight distance and the relocated TWSC alternative resulted in a lower benefit/cost ratio than the roundabout. Georgiaâs draft roundabout in-service review found that all legs are operating at LOS A with the following crash reductions: 83% (total crashes), 82% (injury crashes), and 100% (fatal crashes). Indiana General Approach to Alternative Intersections In determining the appropriate intersection type, Indiana believes that it is important to consider the suitability of the various alternative intersection types for each project. Indiana developed the Intersection Decision Guide (IDG) (Bowen et al. 2014) in 2014 in an effort to promote the use of alternative intersections in Indiana, to provide guidance for the process of selecting an intersection type, and to encourage documentation of decision-making for inter- sections. The IDG incorporates concepts from the FHWA Alternative Intersection Guides (Steyn et al. 2014; Schroeder et al. 2014; Hummer et al. 2014a; Hummer et al. 2014b). Although the IDG accommodates any intersection type, it explicitly covers the following nine intersection types: conventional intersection, MUT, roundabout, CFI, jughandle, offset T, CGT, QRI, and grade separation. A technical brief for each intersection type is provided in the IDG Appendix. The IDG outlines a two-stage process in which candidate intersection types undergo an initial feasibility screening in Stage 1 and feasible alternatives are further scrutinized based on relative performance in Stage 2. Considerations for Stage 1 include site and geometric characteristics, project purpose, general performance expectations, environmental impacts, and time required for project development. Stage 2 includes a performance evaluation with respect to safety, opera- tions, cost-effectiveness, and other factors such as environmental and right-of-way effects. The IDG includes decision trees to guide the user through the decision-making process. To help standardize traffic analysis procedures, notably simulation, Indiana developed an Intersection Traffic Analysis Procedures document (Indiana DOT 2018). The Indiana Design Manual (Indiana DOT 2013) chapter on interchanges includes some information on DDIs, SPDIs, and roundabout diamond interchanges. The current chapter on intersections does not specifically address alternative intersections, but includes guidance for design features related to alternative intersections such as median openings and acceleration lanes. A ready-to-be published update to the design manualâs intersection chapter does prescribe select design features for alternative intersections, such as the proper offset distance of U-turns from the central intersection for superstreets and MUTs. Experiences with Alternative Intersections In addition to roundabouts, Indiana currently has the following alternative intersection types in operation: three DDIs, six SPDIs, and four superstreet intersections (unsignalized J-turns). Indiana also has numerous alternative intersections in the design phase or under serious consideration, including CGTs, MUTs, CFIs, and DDIs. Indiana recently initiated a project, the first of its type in the state, to implement alternative intersections comprehensively across a road corridor, as opposed to the prior practice of introducing them in isolation. In addition, Indiana is designing hybrid forms of alternative interchanges and intersections, including hybrid CFI/MUT intersections and an interchange that incorporates CGT concepts. These
Case Examples 59 hybrids are currently either programmed or in the design stage. The CFI/MUT hybrids were created to address the constraint of close proximity to interchanges that precludes the use of a U-turn opening on both sides of the intersection. A conceptual drawing for the CFI/MUT hybrid at SR-66 and Epworth Road in Evansville, Indiana, is shown in Figure 50. Indiana has performed some informal before/after evaluations of superstreets that have shown positive results for safety, including reductions in severe crashes of 60% to 80%. Indiana has also generally found alternative intersections to be effective at alleviating congestion. Some of Indianaâs takeaways from its experiences with alternative intersections include the following (Steckler 2018): ⢠Keep analysis of choices simple to the extent practicable; ⢠Actively seek assistance and guidance from FHWA and other DOTs; ⢠Allow the use of engineering judgment; ⢠Increase awareness of alternative intersections within the agency to increase their consider- ation and selection; and ⢠Anticipate internal and external resistance to non-traditional intersection and interchange forms, although it will fade over time as safety and operational benefits become evident. Challenges to Implementation Some of the challenges Indiana has faced regarding alternative intersections include devel- oping design details with limited available guidance, providing accommodations for bicyclists and pedestrians, and overcoming public resistance. Indiana would like to see additional design guidance developed for elements such as U-turn spacing on superstreets and MUTs and lighting. (Courtesy Indiana DOT) (Imagery ©2019 Google, Imagery ©2019 IndianaMap Framework Data, Maxar Technologies, USDA Farm Service Agency, Map data ©2019 Google) Figure 50. Layout drawing of CFI/MUT hybrid at SR-66 and Epworth Road in Evansville, Indiana.
60 Alternative Intersection Design and Selection In addition, Indiana would like to enhance its processes to incorporate considerations for bicyclists and pedestrians at alternative intersections. Other opportunities for growth in Indiana with respect to its alternative intersection practices include greater incorporation of corridor considerations and creating a more responsive and interactive decision guide (Steckler 2018). Indiana has met some public resistance to alternative intersections, especially because of the novelty of the designs. Some of the concerns have related to the additional travel times incurred to select movements when left-turn movements are re-routed at superstreets. To help address the publicâs concerns regarding alternative intersections, Indiana has placed greater emphasis on having thorough conversations with local communities on each project. In addition, Indiana has developed public outreach websites for superstreets and MUTs (Indiana DOT 2019b, Indiana DOT 2019c) that include overviews, information on benefits, and videos. Indiana also creates project-specific flyers and pamphlets, especially when the intersection type is new to the region. Project Highlight: I-69 and SR-1 DDI near Fort Wayne, Indiana Indianaâs first DDI at I-69 and SR-1 (Dupont Road) (Figure 51) was opened in 2014, costing $3.5 million (Indiana DOT 2019a). The previous conventional diamond interchange (CDI) was experiencing high levels of congestion, with several approaches projected at LOS F in 2030 (USI Consultants 2010). The other alternatives considered were additional ramp widening and auxiliary lane modifications, SPDI, and a roundabout interchange. It was determined that a two-lane roundabout interchange did not meet the project purpose and need because it would reach LOS F in 2030. The DDI was selected as it had the lowest projected cost of the remaining feasible alternatives. An SPDI was estimated to cost $6.1 million. The project received the Civil Engineering Project of the Year award from the American Society of Civil Engineers (ASCE), Indiana section, and an Honor Award for Engineering Excellence from the American Council of Engineering Companies of Indiana (Indiana DOT 2019a). (Imagery © 2019 Google, Imagery ©2019 IndianaMapFrameworkData, Maxar Technologies, U.S. Geological Survey, USDA Farm Service Agency, Map data ©2019 Google) Figure 51. DDI at I-69 and SR-1 (Dupont Road) near Fort Wayne, Indiana.
Case Examples 61 Minnesota General Approach to Alternative Intersections Minnesota implemented its first ICE Policy in 2007 and revised its ICE Policy Manual in 2017 (Minnesota DOT 2017a). Minnesota developed an ICE Policy because it believed that a signal justification report did not provide sufficient flexibility to explore other options. The Minnesota ICE Policy includes two phases: scoping and alternative selection. Minnesota has found that the ICE policy helps to promote the use of alternative intersections in Minnesota. Regarding analysis tools, roundabout analyses are usually performed with Rodel software (Rodel Interactive North America, LLC 2019) and VISSIM (PTV Group n.d.) is typi- cally used for operational analyses of other alternative intersections. The CMFs from the CMF Clearinghouse (FHWA 2019a) are used to evaluate the safety effects. Minnesota developed design guidance for roundabouts as part of its design manual (Minnesota DOT 2018) and design and implementation guidelines for superstreets and DDIs (Minnesota DOT 2016a, Minnesota DOT 2017c). The superstreet and DDI guidelines include information on design, operations, signing, marking, lighting, and other considerations such as pedestrian and bicycle facilities. Experiences with Alternative Intersections Minnesota currently has the following alternative intersection facilities open and opera- tional: roundabouts, superstreets, MUTs, SPDIs, DDIs, and CGTs. Minnesota uses the term reduced conflict intersections (RCIs) for its superstreets. With the exception of the SPDI, many of these intersection types are also in the design or planning stages of project development. Minnesota is satisfied with the performance of its alternative intersections. Minnesota believes that the DDIs are working well, and there have been no intersection-related fatal or serious injury crashes at any of the approximately 30 superstreet intersections. Minnesota performed studies to document the safety benefits of roundabouts and superstreets (Leuer 2014, Leuer 2017, Leuer and Fleming 2017, Leuer 2018). Various considerations led to the implementation of DDIs in Minnesota. For example, a significant factor that led to the I-494 and 34th Avenue interchange becoming a DDI was the ability to keep the light rail line to Minneapolis-St. Paul International Airport open during construction. Minnesota does not have any plans for future SPDIs, because of concerns about pedestrian and bicyclist accommodations, the need for large bridge structures, and the inability for future expansion. Minnesota has not implemented any CFIs, because project conditions such as traffic volumes and right-of-way availability have not been suitable for a CFI. Challenges to Implementation Minnesota has encountered public resistance on many alternative intersection projects, especially roundabouts and superstreets. The public has become more accepting of round- abouts in urban areas such as Minneapolis/Saint Paul after gaining exposure to roundabout designs. Concerns expressed by the public regarding superstreets include additional travel time and the perceived counterintuitive nature of the design. Minnesota developed public out- reach videos for superstreets (Figure 52) and sponsored two studies to address concerns about trucks and large farm vehicles using superstreets (Hallmark et al. 2016, Hawkins et al. 2015). In Minnesotaâs experience, advanced planning for public outreach efforts on superstreets is benefi- cial. Minnesota would like to learn more about other statesâ public outreach efforts for alterna- tive intersections.
62 Alternative Intersection Design and Selection Other challenges as described by Minnesota in its implementation of alternative inter- sections include high cost for some alternative intersection projects, finding ways to accom- modate bicyclists and pedestrians (especially at roundabouts), and the potential for sideswipe crashes at multilane roundabouts. Minnesota would like to see continued growth for alterna- tive intersections. Minnesota has found that intersection types can sometimes fall in and out of favor depending on priorities and perceptions. For example, SPDIs were once popular in Minnesota, but further implementation of SPDIs in the state is unlikely. Project Highlight: US 212 at MN 284 in Cologne, Minnesota (Superstreet) A superstreet was constructed at the existing intersection of US 212 and MN 284 in Cologne, Minnesota, in 2012 as shown in Figure 53. Before the superstreet conversion, the intersection was experiencing approximately one fatal right-angle crash each year. The current approximate annual average daily traffic is 13,000 vehicles per day on US 212 and 3,000 vehicles per day on the minor approaches. A superstreet was chosen because a signal was not deemed a good solution, and an interchange would have been costly. No severe crashes have occurred at the intersection since the superstreet was built. The design included accommodations for fire trucks to cross the median directly instead of turning right and making a U-turn. After the project opened to traffic, the fire trucks decided to turn right and make the U-turn because Emergency Medical Services found that the amount of additional travel time was insignificant. A future planned expansion of the four-lane section of the US 212 corridor calls for the intersections to either be closed or implemented as superstreets or MUTs. (Minnesota DOT 2017b) Figure 52. Screenshot from Minnesota public outreach video for superstreets. (Imagery © 2019 Google, Imagery ©2019 Maxar Technologies, U.S. Geological Survey, USDA Farm Service Agency, Map data ©2019 Google) Figure 53. Superstreet at US 212 and MN 284 in Cologne, Minnesota.
Case Examples 63 Missouri General Approach to Alternative Intersections Although Missouri does not currently have an ICE policy, it frequently considers alternative intersections as cost-effective ways to improve safety and operations. Missouri often identi- fies alternative intersection configurations as solutions to problems that cannot be addressed by conventional intersections. To allow for flexibility with configurations and measures of effectiveness, Missouri typically uses micro-simulation for operational analyses of alterna- tive intersections. Missouri provides some guidance for DDIs and superstreets (Missouri uses the term J-Turns for superstreets) in its Engineering Policy Guide (EPG) (Missouri DOT 2017, Missouri DOT 2018a, Missouri DOT 2019). The DDI section of the EPG covers many topics such as design elements, modeling, spacing of adjacent intersections, operation, maintenance, and public involvement. The superstreet (J-turn) guidance in the EPG includes signing details. Missouri also sponsored studies (Sun et al. 2016; Claros et al. 2017; Sun et al. 2017) that developed design guidance for U-turn spacing and acceleration and deceleration lanes for superstreets (J-turns). Experiences with Alternative Intersections The first DDI in the United States opened in Springfield, Missouri, in 2009. Missouri learned about the DDI concept from a presentation by FHWA. Missouri developed a lessons learned report (Missouri DOT 2010) based on its experiences with its first DDI at I-44 and SR-13 (Kansas Expressway) in Springfield, Missouri. The agency had 23 DDIs in operation in 2019. Other DDI installations are currently in the design phase or under consideration. Missouri has found the DDI to be effective at eliminating the congestion problems that previously existed at the interchange locations. In addition, Missouri sponsored a study (Claros et al. 2015) that documented the safety benefits of a DDI. Based on site characteristics, pedestrians are accom- modated in the median or on the outside of the bridge. Missouri also has approximately 20 superstreet intersections open and operational, mostly on rural divided expressways. Several superstreet intersections are also in the design stage or under consideration. The need for superstreet intersections was driven by Missouriâs Strategic Highway Safety Plan and 2009 Intersection Safety Plan. Missouri has obtained significant crash reductions from implementing superstreets and sponsored studies (Edara et al. 2015; Claros et al. 2017) that documented their benefits and investigated their operational and safety effects. Missouri has also developed some hybrid forms of alternative intersections. Two DDIs with roundabouts at one end of the interchange were completed in 2017 and 2018 (Hale 2016, Hale 2019). One location (I-49 at 155th St.) includes a single-lane roundabout (Figure 54) while (Missouri DOT 2018b) Figure 54. DDI/roundabout interchange at I-49 and 155th Street in Grandview, Missouri.
64 Alternative Intersection Design and Selection a multilane roundabout is used at the other site (US-51 at SR-291S). The concepts for these designs were developed because of the close proximity of an outer road to the interchange. Missouri believes that these intersections are performing well, although some issues with speed and drivers failing to yield at the multilane roundabout remain. Missouri also has approximately 200 roundabouts open and operational on the state system with some additional roundabouts in the design or planning stages. Missouri built one CFI near St. Louis after learning about the CFI concept from Louisiana. Although the CFI has performed well, Missouri does not have any plans for future CFIs because of the high right-of-way require- ments and access management needs. Missouri also has several open and operational SPDIs, but believes future SPDIs are unlikely because of concerns about high cost, visibility, lane assign- ment, and applicability being limited to cases with balanced left turns. Missouri described some general takeaways from its experiences with alternative inter sections, summarized as follows: ⢠Human factors need to be considered (e.g., overhead signs can imply higher speed). ⢠Driver expectancy needs to be considered. ⢠The design (especially signing and pavement markings) should guide drivers through the intersection. ⢠Lane assignments are critical, and overhead signing may be required. ⢠Solving the problem needs to be the focus. ⢠More than one solution might exist. Challenges to Implementation In Missouriâs experience, the public has been more accepting of DDIs than superstreets or roundabouts. Stakeholder concerns related to superstreets include additional travel time caused by the re-routing of traffic movements and potential adverse affects to businesses. For a project that involved several superstreet intersections along US-54, Missouri formed an advisory committee that helped to prioritize locations and garner greater public support. The public has generally been supportive of DDIs to the point where some communities expect a DDI. On one interchange project, the public actually preferred a DDI over a conventional diamond even though the conventional diamond was determined to be the best solution. Mis- souri has developed a variety of public outreach materials and has found three-dimensional visualizations to be more effective than overhead drawings to help the public understand alter- native intersections. Other challenges Missouri experienced with respect to alternative intersections include the following: ⢠Phasing can be difficult especially when new movements are re-routed in the same location (e.g., DDI, roundabout); ⢠Contractors frequently make changes to traffic plans that can affect long-term maintenance; ⢠Left-turn-on-red is prohibited in Missouri; ⢠Off-tracking by large trucks turning at DDIs may require additional pavement; and ⢠Vehicle speeds through a DDI need to be controlled. Moving forward, Missouri is seeking greater uniformity in its alternative design practices and is beginning to look at corridors instead of individual locations. Some study needs iden- tified by Missouriâs staff include more guidance for accommodating turning movements for large trucks and information regarding the suitability of superstreet intersections based on traffic volumes.
Case Examples 65 Project Highlight: I-35 at SR-152 in Kansas City, Missouri (Displaced Left-Turn Interchange) A displaced left-turn interchange was under construction at I-35 and SR-152 in Kansas City in 2019 (Figure 55) (Hale 2019). This interchange was part of a project that includes interchange improvements and corridor improvements such as additional travel lanes. The project was pro- grammed to address operational and safety concerns and to accommodate projected future growth in the area. The displaced left-turn interchange was chosen as the preferred alternative because a CDI would not provide enough left-turn capacity, a DDI would not provide sufficient capacity for through movements, and an SPDI would not be efficient because of unbalanced left-turn volumes. Operational analyses using micro-simulation found that the proposed configuration would result in 30% less travel time and 45% less delay than a CDI. Texas General Approach to Alternative Intersections Texas does not have an ICE policy, but considers alternative intersections for many projects. To select an intersection type at a given location, Texas typically first performs a high-level capacity analysis using CAP-X (Jenior, Haas, Butsick, and Ray 2018b). In addition, other fac- tors such as right-of-way footprint are considered in determining the feasibility of different inter section types. Feasible alternatives are evaluated in more depth using micro-simulation or Synchro (Trafficware n.d.) to select the intersection type deemed most appropriate at a given location. In some instances, the Interactive Highway Safety Design Model (FHWA 2019b) has been used by Texas for safety analysis of intersection types. Texas is in the process of developing some guidelines for alternative intersections for its roadway design manual. Experiences with Alternative Intersections Texas has many different intersection types that are open and operational or under develop- ment. Texas has 11 to 25 roundabouts open and operational along with 6 to 10 superstreets, CFIs, and SPDIs, respectively. Texas also has MUTs and DDIs on its highway system. Texas incorporates alternative intersections into corridor projects. For example, a project under devel- opment for operational improvements on I-35 in Comal County includes a partial CFI and the roundabout interchange shown in Figure 56. Texas has generally been satisfied with the opera- tional and safety performance of the alternative intersections under its jurisdiction. (Hale 2019) Figure 55. Rendering of displaced left-turn inter- change at I-35 and SR-152 in Kansas City, Missouri.
66 Alternative Intersection Design and Selection Challenges to Implementation In Texasâ experience, public reaction to alternative intersections has mostly been positive. The public is generally supportive of projects that address big problems. In some instances, changes to access caused by alternative intersections bring some resistance from the public. Texas finds that meeting with stakeholders individually, holding open house meetings, and providing project visualizations are effective ways to address stakeholder concerns regarding alternative intersections. Another challenge Texas identified is the need for more guidance on how to design signal cabinet hardware as specially designed cabinets are sometimes required for alternative inter- sections. Texas is also interested in learning about the results for measures of effectiveness such as crash reductions found by other DOTs. Project Highlight: SH 16 (Bandera Road) at Loop 1604 in San Antonio, Texas (CFI) To address growing congestion problems, Texas constructed a CFI at SH 16 (Bandera Road) and Loop 1604 in San Antonio, Texas (Ripps 2019). A screenshot from a visualization of the intersection is shown in Figure 57. The CFI opened to traffic in the spring of 2019. Texas found that the geometry at this location was ideal for a CFI. The project only affected one driveway that was converted to an entrance-only driveway to accommodate trucks. Additional right- of-way was not required for the project, and the existing Loop 1604 bridges were not affected. The alternatives considered were a DDI, an SPDI, and adding lanes to the existing diamond interchange. The CFI provided better operational performance at a lower cost than the other alternatives and was chosen as the preferred alternatives based on several evaluation factors such as meeting the project purpose and need, improving LOS and safety, cost, constructa- bility, right-of-way requirements, visual and noise effects, and impact on adjacent roadways. (Texas DOT 2017) (Imagery ©2019 Google, Imagery ©2019 CAPCOG, Maxar Technologies, USDA Farm Service Agency, Map data ©2019 Google) Figure 56. Conceptual drawing of proposed roundabout interchange at I-35 and Business 35/ Schmidt Avenue in Comal County, Texas.
Case Examples 67 Texas plans to perform some evaluations of this CFI in the future, but has been pleased with its performance in the short time it has been open to traffic. Texas encountered several challenges during the design and implementation of this CFI. One challenge was the need for a specially designed traffic signal cabinet, because the number of phases for the CFI was greater than the number of phases for a typical cabinet. The special order for the signal cabinet took several months to process. Based on guidance that the San Antonio District received from other Texas districts, large overhead signs and directional lane signing for each signal head were provided. The signals were switched over to the CFI configuration during a weekend closure. There were some traffic backups during the evening and weekend closures, and the project was near several retail establishments. Case Examples Summarized The six DOTs described in this chapter have diverse experiences with respect to alternative intersections. Some of the key findings from the DOT interviews can be summarized as follows: ⢠The suitability of the various alternative intersection types for each project is an important consideration used by DOTs in the selection process. ⢠DOTs have benefited from learning about the experiences of other states through direct peer contact, published research, and FHWA assistance. ⢠DOTs use a variety of approaches and tools (e.g., ICE policies, micro-simulation, CAP-X, and custom agency tools) for alternative intersection evaluation and selection. ⢠Some of the DOTs are trying new alternative intersection forms such as hybrids (e.g., CFI/ MUT or DDI/roundabout). ⢠SPDIs appear to be falling out of favor with some DOTs. ⢠Some of the DOTs are moving toward looking more at corridors instead of individual intersections. ⢠The level of public opposition often varies among projects and alternative intersection types, but increasing familiarity can help to reduce both public and internal resistance. ⢠Research needs identified by the DOTs include the development of additional design guid- ance for alternative intersections, especially related to signing, pavement markings, and signal cabinets, and improvements in public education efforts. Figure 57. Screenshot from visualization video of CFI at SH 16 (Bandera Road) and Loop 1604 in San Antonio, Texas. (Texas DOT 2016) (Imagery ©2019 Google, Imagery ©2019 CAPCOG, Maxar Technologies, USDA Farm Service Agency, Map data ©2019 Google)
