Double Crossover Versus Conventional Diamond Interchanges Both with Frontage Roads

Journal of TransporTaTion A Journal of TransporTaTion of the institute of Transportation Engineers advancing transportation knowledge and practices for the benefit of society VolumE 4, issuE i Senior Editor Dr. Lester A. Hoel, P.E., FITE l.a. lacy Distinguished professor of Engineering Emeritus University of Virginia Assistant Senior Editor Dr. Dennis L. Christiansen, P.E., FITE Director Texas Transportation Institute TX A&M University System Dr. Max Donath professor of mechanical Engineering and Director, intelligent Transportation systems institute University of Minnesota Dr. Adib Kanafani professor of the Graduate school University of California, Berkeley Dr. John M. Mason, Jr., P.E., FITE associate provost & Vice president for research Auburn University Dr. Kumares C. Sinha, P.E., FITE olson Distinguished professor school of Civil Engineering Purdue University Dr. Joseph M. 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InSTITuTE oF TrAnSPorTATIon EngInEErS 1627 Eye Street, NW, Suite 600, Washington, DC 20006 USA P: 202.785.0060 F: 202.785.0609 www.ite.org VoLuME 4 | NuMBER I | NoVEMBER 2012 Journal of TransporTaTion of the institute of Transportation Engineers Double Crossover Versus Conventional Diamond 1 interchanges Both with frontage roads By Jorge A. Martinez, E.I.T., M.I.T.E. and Ruey Long Cheu, Ph.D., P.E., M.I.T.E. predicting Trip Generation Characteristics 19 of power Centers By Daniel J. Findley, Ph.D., P.E., Christopher M. Cunningham, M.C.E., P.E., William Letchworth, M.C.E., P.E., and Michael A. Corwin The unique Characteristics of urban 29 Container Trucks By Garreth Rempel, Ph.D., P.Eng. and Jeannette Montufar, Ph.D., P.Eng., PToE CoNTENTS Journal of TransporTaTion 1 The double crossover diamond interchange (DCDI) is a relatively new interchange design that may be able to replace the conventional diamond interchange (CDI). The few DCDIs in operation in the united States were constructed in locations without a frontage road, and only limited research has similarly focused on interchanges without a frontage road. This research proposed a three-phase signal sequence and tested the operational performance of a DCDI, at a freeway interchange with frontage roads, under a variety of traffic demand scenarios. The operational performance of the DCDI was compared with that of a CDI. SYNCHRo was used to optimize the signal timing plans and calculate the intersection delay, intersection level of service, and delay of through movements on the frontage roads. VISSIM was then used to evaluate the total network travel time, total network delay, total number of stops, and average travel times of selected movements across the interchange (two intersections). Double Crossover Versus Conventional Diamond interchanges Both with frontage roads By Jorge A. Martinez, E.I.T., M.I.T.E. and Ruey Long Cheu, Ph.D., P.E., M.I.T.E. Introduction The diamond interchange has been one of the most common interchange designs that connect a freeway with a major arterial crossing. a diamond interchange consists of two closely spaced intersections. Compared with other interchange designs, the diamond interchange entails a minimal right of way but requires priority or signalized control.1 for the rest of this article, this type of diamond interchange is referred to as the conventional diamond interchange (CDi). The double crossover diamond interchange (DCDi), also known as the diverging diamond interchange, is a relatively new interchange design. The DCDi requires similar right of way as the CDi; it also has two intersections. in a DCDi, the through traffic along the arterial approaches the in- 2 ThE insTiTuTE of TransporTaTion EnGinEErs terchange on the right-hand side of the divided roadway, crosses over to the left-hand side of the divided roadway at the first intersection, passes under or over the freeway on the left-hand side of the divided roadway, and then crosses back to the right-hand side of the divided roadway at the second intersection. Traffic signals at the two intersections require only two phases to cater to the opposing (crossover) through movements. Vehicles making left turns at an intersection may thus bypass the traffic signals.2 The first-known DCDi, at Versailles, france, has been in operation for more than 25 years.2 The concept of DCDi was introduced into the united states in 2000. as of february 2012, there are 12 operational DCDis in missouri, utah, Tennessee, and Kentucky, and several more are under construction or being planned.3 research conducted over the past decade has indicated that DCDi offers many advantages over CDi primarily because of its efficient two-phase signal operation, fewer conflict points, and reduced vehicular delay (especially for the left-turn movements).2 however, the few operational DCDis and most of the experimental models are based on sites where freeway frontage roads do not exist, or there is no need to facilitate vehicular travel between the freeway offand on-ramps. The objectives of this paper are (1) to propose and test a signal phase sequence that permits the implementation of DCDis at freeways with parallel frontage roads; (2) to comparatively evaluate the operational performance of a DCDi with frontage roads (DCDi-fr) against a CDi with frontage roads (CDi-fr). an existing CDi-fr site in El paso, TX, usa, is selected to design, code, calibrate, optimize, and simulate the DCDi-fr and CDi-fr models in sYnChro and Vissim for the comparative evaluation. The measures of effectiveness (moEs) are the average intersection delay, intersection level of service (los), total network (interchange) travel time, total network delay, total number of stops, average delay for the through movements along the frontage roads, and average section delay for the through and left-turn movements that traverse the interchange (two intersections). This research contributes to the feasibility of implementing DCDi-fr at freeway interchanges with frontage roads, and a better understanding of the advantages and disadvantages of the DCDi-fr relative to the CDi-fr. This research should be of interest to highway agencies that manage freeways with frontage roads. Review of Past Research Chlewicki has summarized the concept and history of DCDi in the united states.3 The federal highway administration (fhWa), having performed some tests on DCDi, also maintains a website with its findings.2 in perhaps the earliest study of DCDi in the united states, sYnChro was used to optimize the signal timing plans and to compare the operational performance of a DCDi and a CDi with a fixed set of traffic demands.4 results indicated that the DCDi had lower delays for the left-turn and through movements compared with the CDi. Bared et al. and Edara et al. performed simulation tests on a four-lane and a six-lane DCDi, each with five different levels of traffic demand.5, 6 They used TransYT-7f to optimize the signal timing plan, followed by using Vissim to simulate the traffic operations. The results were compared with those obtained for the CDi, but the CDi’s signal timing plans were optimized by passEr-3. The DCDi showed a clear advantage over the CDi for all high-demand traffic scenarios, in terms of lower delays, fewer stops, and shorter queue lengths. in low-and medium-demand scenarios, both interchange designs have similar performance measures or outcomes. sharma and Chatterjee7 followed a similar methodology as in Bared et al. and Edara et al.,5,6 and tested both interchange designs with different volume scenarios. in sharma and Chatterjee, the signal timing plans were optimized by sYnChro.7 The output provided by the Vissim simulation models showed that the DCDi had higher capacity and lower delay for the left-turn movements. Journal of TransporTaTion 3 another study performed by stanek compared the advantages and disadvantages of several diamond interchange designs, including the DCDi.8 The study used sYnChro to optimize signal timing plans and Vissim to simulate the traffic operations. stanek reported that the DCDi has high interchange capacity, and also noted that signal coordination in a DCDi is less critical than other interchange designs. afshar et al. used Vissim to compare the performance of a DCDi with a single point urban interchange (spui).9 The signal timing plans of the DCDi and spui were optimized by sYnChro and entered into Vissim for simulation. for balanced flow conditions, the capacity of the spui was found to be higher than that of the DCDi. for unbalanced flow conditions, the DCDi had lower delays than the spui. Because of the crossover movements at the DCDi, one of the frequently mentioned concerns was the unfamiliarity of the drivers with the interchange design. The fhWa, in collaboration with missouri Department of Transportation, evaluated human factor aspects of the DCDi design in an in-laboratory driving simulator.10 none of the 74 participants who took part in the experiment were observed crossing into an oncoming traffic lane in the DCDi model. This study also found that, because of the curvature at the approach of the DCDi, the speed at the crossing points was about 8 mph slower than that of the CDi. more recently, Chlewicki presented several options for designing and coordinating the signal splits at DCDis to maximize the progression of traffic along the arterial.11 Because of the DCDi’s potential popularity and benefits, the fhWa has included it in the Alternative Intersections/Interchanges: Informational Report.12 The above studies have led to the general conclusions that DCDi is a safe and relatively more efficient intersection than CDi. however, the findings are based on sites where there is no freeway frontage road. in u.s. states such as Texas, michigan, minnesota, and Washington, many urban areas have parallel one-way frontage roads on both sides of the freeways. at these sites, the interchange designs need to cater for the through movements along the frontage roads. it appears that, at each intersection of a DCDi, an additional signal phase is necessary to cater for the through movement on the frontage road. Then, each individual intersection will be operating with a threephase signal timing plan, which is the same as in a CDi. it remains to be seen how the signal phases at the two intersections of a DCDi-fr may be coordinated, and how efficient the timing plan design would be compared with the CDi-fr, especially on left-turn movements. Experimental Plan The following steps were taken to evaluate the operational performance of a DCDi-fr and compare it with a CDi-fr: 1. an existing CDi-fr site was selected to model both interchange designs. 2. The selected interchange’s signal timing plan, traffic volume, vehicle composition, and section travel times were collected at the peak hour of a typical weekday. 3. The CDi-fr model was developed in Vissim. The average section travel times for the selected interchange movements produced by the Vissim model were compared with the corresponding average section travel times collected in the field in step 2. The Vissim model parameters were adjusted until the average section travel times between the Vissim output and the field data did not have a statistically significant difference. 4. The traffic demand scenarios to be tested were identified. 5. The DCDi-fr and CDi-fr models, based on the selected site, were developed in sYnChro. The calibrated Vissim parameters determined in step 3 were translated and entered into the equivalent parameters in the sYnChro models. a three-phase signal timing plan was proposed 4 ThE insTiTuTE of TransporTaTion EnGinEErs Figure 1. Aerial photograph of the site (Pellicano Dr. and Joe Battle Blvd. interchange). Figure 2. Geometric layout of CDI-FR (Pellicano Dr. and Joe Battle Blvd interchange). Source: Photo courtesy of Geospatial Information Service Center, The University of Texas at El Paso. Journal of TransporTaTion 5 for the DCDi-fr. for each interchange design and traffic demand scenario, the signal cycle length, splits, and offset were optimized by sYnChro. The moEs extracted from the sYnChro models for comparisons were average intersection delay, intersection los, and average delay for the through movement along frontage road. 6. The Vissim model for the DCDi-fr was then developed, with the calibrated parameters described in step 3. The optimized signal timing plans obtained from sYnChro were coded into the Vissim’s DCDi-fr and CDi-fr models. six travel time sections were identified in the Vissim models to capture the through and left-turn movements that traverse the interchange. Vissim simulations were made for the same set of traffic demand scenarios identified in step 4. The moEs extracted from the Vissim models for comparisons were total network (interchange) travel time, total network delay, total number of stops, and average section travel time. Site Selection and Data Collection The El paso site selected for this study was the interchange of pellicano Dr. (the arterial running in the east-west direction) and Joe Battle Blvd. (the frontage roads that parallel the loop 375 freeway, running in the north-south direction). an aerial view of the site is shown in figure 1. This interchange was selected because it is the only CDi-fr in El paso that could be recorded with the traffic surveillance cameras owned and operated by the Texas Department of Transportation (TxDoT). figure 2 shows the geometric layout of the interchange, which consists of the east intersection (labeled as E) and west intersection (labeled as W). The center-to-center distance between the two intersections is 320 ft. Travel time markers (lamp posts or signs) were identified at approaches upstream and downstream of the interchange. They are represented by markers 1 to 8 in figure 2. The interchange currently operates with the “Texas four-phase” strategy.13 The phase sequence is shown in figure 3(a). field data were collected on December 10, 2009 (Thursday), from 7:00 to 8:00 a.m. During this am peak hour, video recordings were made by TxDoT surveillance cameras, from which traffic volume and vehicle composition were later counted in the laboratory. The floating car survey method was used to measure the travel times of four through movements (from markers 1 to 2, 3 to 4, 5 to 6, and 7 to 8, respectively). signal timing data were measured in the field and counterchecked with the data provided by the City of El paso.                         (a) CDI-FR (b) DCDI-FR Figure 3: Signal phase sequences for CDI-FR and DCDI-FR.  4 6 4 5 2 5 2 8 1 6 1 8 4 8 1 5 2 6 The numbers represent the National Electronic Manufacturers Association (NEMA) phases.  West Intersection East Intersection West Intersection East Intersection Figure 3: CDI-FR and DCDI-FR signal phase sequences. 12 ThE insTiTuTE of TransporTaTion EnGinEErs in Vissim, users are able to record the travel times of vehicles between two fixed markers, similar to a license plate survey. This feature was used to gather section travel time data for analysis. six travel time sections were defined in the Vissim’s DCDi-fr and CDi-fr models: (1) markers 5 to 6 (eastbound through movement), (2) 7 to 8 (westbound through movement), (3) 5 to 2 (eastbound turning left), (4) 7 to 4 (westbound turning left), (5) 1 to 8 (northbound turning left), and (6) 3 to 6 (southbound turning left). These six sections consisted of multiple links in the Vissim model, and passed two intersections. for each combination of v1 and v2 values and a specific section, the average section travel times and average section delays between the two interchange designs were compared. although the two interchange models have the same marker locations, the section travel time still depends on the distance between the upstream and downstream markers. average section delay can better convey the disutility encountered by drivers owing to the interchange designs and signal control strategies. in Vissim, the section delay includes the delay from signal control but excludes the delay from lower speed limits while passing the interchange (the lower speed limits were implemented in the model using the “speed reduction area” feature during the model calibration). figure 7 plots the average section delay of the eastbound through movement (from markers 5 to 6) that passed the two intersections. Each line in the graph represents a particular interchange design with a fixed v1 value (through volume from the frontage road); v2, the left-turn volume, is plotted along the horizontal axis. a similar chart for the westbound movement (markers 7 to 8) exhibits the same patterns. from this figure, it can be inferred that when v2 ≤ 500 vph, the through vehicles along the arterial have lower average delays with the CDifr. however, when v2 ≤ 700 vph, the average section delays with the CDi-fr become much longer than those with the DCDi-fr. increased delays occur because, in the CDi-fr, at high v2, the left-turn vehicle queue may spill over to the through lane and thus obstructs the through vehicles. This has been verified by observing the Vissim animation during the simulation runs. The DCDi-fr prevents this problem because it has a higher capacity for the left-turning vehicles. figure 8 presents the average section delay plots for eastbound vehicles that traveled past the west intersection and then turned left at the east intersection. The travel times and hence delays were  0 50 100 150 200 250 300 400 500 600 700 800 Average Section Delay (s) v 2 (vph) CDI-FR v1=500vph CDI-FR v1=600vph CDI-FR v1=700vph CDI-FR v1=800vph DCDI-FR v1=500vph DCDI-FR v1=600vph DCDI-FR v1=700vph DCDI-FR v1=800vph Figure 7. Average section delay for eastbound through vehicles along the arterial. Journal of TransporTaTion 13  0 50 100 150 200 250 300 400 500 600 700 800 Average Section Delay (s) v 2 (vph) CDI-FR v1=500vph CDI-FR v1=600vph CDI-FR v1=700vph CDI-FR v1=800vph DCDI-FR v1=500vph DCDI-FR v1=600vph DCDI-FR v1=700vph DCDI-FR v1=800vph Figure 8. Average section delay for eastbound vehicles turning left at the east intersection.  0 50 100 150 200 250 300 300 400 500 600 700 800 Average Section Delay (s) v 2 (vph) CDI-FR v1=500vph CDI-FR v1=600vph CDI-FR v1=700vph CDI-FR v1=800vph DCDI-FR v1=500vph DCDI-FR v1=600vph DCDI-FR v1=700vph DCDI-FR v1=800vph Figure 9. Average section delay for southbound vehicles turning left at the west intersection. 14 ThE insTiTuTE of TransporTaTion EnGinEErs measured from markers 5 to 2. The chart for westbound vehicles turning left at the west intersection (markers 7 to 4) has similar patterns and therefore is not shown here. at low traffic volume, v2 = 300 vph, both the DCDi-fr and CDi-fr experienced similar magnitude of average delay to the leftturn vehicles from the arterial. however, when v2 > 500 vph, the DCDi-fr clearly has lower average delays compared with the CDi-fr. The longer average delay experienced by the left-turn vehicles in the CDi-fr is due to near-capacity demand in the left-turn lane. The difference in average delays increases exponentially with v2 value. figure 9 plots the average section delay for the southbound vehicles (from the frontage road) that turned left at the west intersection and proceeded eastbound past the east intersection. The travel time section was from markers 3 to 6. The chart for the average section delays for the northbound vehicles (from the frontage road) that turned left at the east intersection and passed the west intersection (from markers 1 to 8) has similar patterns. figure 9 clearly shows that when the leftturn volume is v2 > 400 vph, the DCDi-fr is more advantageous than the CDi-fr because its average section delay is lower. The reduced average section delay in the CDi-fr is due to signal-controlled left-turn movements. in addition, at high v2 values, vehicles queuing to make left turns in the links between the two intersections may prevent other vehicles from making left turns from the frontage roads. in contrast, left turns in the DCDi-fr were managed through “yield-on-entry” strategies, thereby mitigating the abovementioned problems. Conclusions This research has proposed and tested a three-phase sequence for the efficient implementation of signal timing plans at a DCDi-fr. at each intersection, two of the signal phases followed that of a DCDi (for the two crossover movements), but a third phase is added to accommodate the through movements on the frontage roads. after optimizing the cycle lengths, splits, and offsets of the DCDifr and CDi-fr models in sYnChro, the optimized cycle length of the DCDi-fr was found to be shorter than or equal to that of the DCi-fr, with the same traffic demand. With the same traffic demand, sYnChro also estimated that the intersections in the DCDi-fr have lower average delays and equal or better los than the intersections in the CDi-fr. however, the through movements at the frontage roads experienced longer delays in the DCDi-fr than the CDi-fr when the left-turn volume is low. The evaluation conducted by Vissim simulations showed that, at the same traffic demand levels, the DCDi-fr always resulted in lower total network (interchange) travel time, lower total network delays, and fewer stops. The improved operational performance of the DCDi-fr is due to the design that favors left-turn movements. Vehicles making left turns from the frontage roads and from the arterial do not need to be delayed by the traffic signals. most of the moEs at the section, intersection, and network levels have shown that the DCDi-fr provides a better operational performance than the CDi-fr. Table 5 summarizes the findings. Journal of TransporTaTion 15 Table 5. Differences between CDI-FR and DCDI-FR. CDI-Fr DCDI-Fr Interchange features ■Vehicles travel on the right-hand side of the divided roadway along the arterial on top or below the freeway. ■Left-turn movements are controlled by signals. ■Up to six signal phases. ■Vehicles travel on the left-hand side of the divided roadway along the arterial on top or below the freeway. ■Left-turn movements are “yield-on-entry.” ■Three signal phases. SYNCHRO modeling results ■Lower delay for through movements on frontage roads. ■Equal or shorter cycle length. ■Lower average intersection delay. ■Equal or better intersection level of service. VISSIM modeling results ■Lower delay for through movement along arterial when the left-turn volume is low. ■Lower total network travel time and delay. ■Fewer stops. ■Lower delay for through movement when the left-turn volume is high. ■Lower delay for left-turn movements. This research is believed to be the first to investigate DCDi implementation at freeway interchanges with frontage roads. it not only has proposed a signal phase sequence for the DCDi-fr, but also has proven that the DCDi-fr operates better than the CDi-fr. The findings may contribute to the eventual implementation of DCDi-frs at actual sites with freeway frontage roads. The above results are obtained from a simulation experiment based on a site with fixed intersection spacing (320 ft. center to center), a fixed number of lanes in each approach, symmetrical traffic demand, and fixed through traffic volume along the arterial (700 vph per direction). many factors that may affect DCDi-fr performance are yet to be fully understood. Examples of these factors are (1) through traffic volume along the arterial, (2) rightturn volume, (3) distance between two intersections, and (4) type of control for left turn from the frontage road into the arterial. The factors are the directions for continuing research. nevertheless, this research has demonstrated the feasibility and advantages of implementing DCDi-fr at freeway interchanges with frontage roads, and opens many possible directions for future DCDi-fr research. Acknowledgments The authors thank the Texas Department of Transportation, El paso District for assistance in field data collection, and the City of El paso Department of Transportation for providing signal timing data. References 1. american association of state highway and Transportation officials. A Policy on Geometric Designs of Highway and Streets, 5th Edition. Washington, DC: aashTo, 2004. 2. federal highway administration (fhWa). Double Crossover Diamond Interchange. office of research, Development, and Technology, office of safety. fhWa, 2010. accessed January 4, 2011. http://www.fhwa.dot.gov/publications/research/safety/09054/index.cfm. 3. Chlewicki, G. The Diverging Diamond Interchange. 2010. accessed february 4, 2012. http://www.divergingdiamond.com. 4. Chlewicki, G. “new interchange and intersection Designs: The synchronized split-phasing intersection and the Diverging Diamond interchange.” Proceedings of the 2nd Urban Street 16 ThE insTiTuTE of TransporTaTion EnGinEErs Symposium, July 28–30, 2003, anaheim, California. Washington, DC: Transportation research Board, 2003. 5. Bared, J. G., p. K. Edara, and r. Jagannathan. “Design and operational performance of Double Crossover intersection and Diverging Diamond interchange.” Transportation Research Record: Journal of the Transportation Research Board, Vol. 1912 (2005): 31–38. 6. Edara, p. K., J. G. Bared, and r. Jagannathan. “Diverging Diamond interchange and Double Crossover intersection—Vehicle and pedestrian performance.” Proceedings of the 3rd International Symposium on Highway Geometric Design, June 29–July 1, 2005, Chicago, illinois. Washington, DC: Transportation research Board, 2005. 7. sharma, s. and i. Chatterjee. “performance Evaluation of the Diverging Diamond interchange in Comparison with the Conventional Diamond interchange.” Proceedings of the 2007 Transportation Scholar Conference, november 9, iowa state university. midwest Transportation Consortium, 2007. 8. stanek, D. “innovative Diamond interchange Designs: how to increase Capacity and minimize Cost.” Proceedings of the Institute of Transportation Engineers 2007 Annual Meeting. pittsburgh, pennsylvania: institute of Transportation Engineers, 2007. 9. afshar, a. m., J. G. Bared, and s. Wolf. “Traffic operational Comparison of a single point and Diverging Diamond interchanges.” The 88th Annual Meeting of the Transportation Research Board, Compendium of Papers DVD. Washington, DC: Transportation research Board, 2009. 10. fhWa. Driver’s Evaluation of the Diverging Diamond interchange. pub. no. fhWahrT-07-048. Washington, DC: fhWa, 2009. 11. Chlewicki, G. “operational Effects of the Diverging Diamond interchange.” The 89th Annual Meeting of the Transportation Research Board Compendium of Papers DVD, Washington, DC: Transportation research Board, 2010. 12. hughes, W., r. Jagannathan, D. sengupta, and J. hummer. Alternative Intersections/Interchanges: Informational Report (AIIR). pub. no. fhWa-hrT-09-060. Washington, DC: federal highway administration, 2010. 13. Chaudhary, n. a. and C.-l. Chu. Guidelines for Timing and Coordinating Diamond Interchanges with Adjacent Traffic Signals. report TX-00/4913-2. Texas Transportation institute, 2000. 14. Trafficware. sYnChro 7. sugar land, Texas: Trafficware ltd., 2009. 15. Transportation research Board. Highway Capacity Manual. Washington, DC: TrB, 2000. 16. pTV. VISSIM 5.00 User Manual. Karlsruhe, Germany: pTV aG, 2007. Journal of TransporTaTion 17 Jorge A. Martinez, E.I.T., M.I.T.E., is a graduate engineer with Walter P. Moore in the El Paso, Texas office. He received his B.S.C.E. and M.S.C.E. in civil engineering from the university of Texas at El Paso (uTEP), in 2008 and 2010, respectively. Jorge was the vice president of the ITE uTEP Student Chapter. He was a recipient of the Dwight D. Eisenhower Transportation Fellowship. He is a member of ITE. Ruey Long Cheu, Ph.D., P.E., M.I.T.E., is an associate professor with the Department of Civil Engineering at the university of Texas at El Paso (uTEP). He has served as the faculty advisor of the ITE uTEP Student Chapter. His research interests include intelligent transportation systems, traffic operations, and public transportation. He is a member of ITE.