Understanding the Contributions of Operations, Technology, and Design to Meeting Highway Capacity Needs (2012) / Chapter Skim
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Pages 52-78
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52 C h a p t e r 4 This chapter presents the results of applying the enhanced DTA model features described in Chapter 2 to test the effectiveness of the selected operational improvement strategies shown in Table 3.2 and to confirm the applicability and usefulness of the developed model. The model was applied in two real-world test networks.
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53 decision makers who must make difficult decisions about when and where to add new lanes of capacity to the existing transportation infrastructure. • Important insights are gained from the enhanced DTA model on the travel time reliability effects of operational improvement strategies.
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54 • Node control type (number of intersections including on- and off-ramps) 44 No control (on- and off-ramps)
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55 over the full analysis period, vehicles were generated 30 minutes before the analysis time period (4:00 to 4:30 p.m.) as well as 30 minutes after the completion of the analysis period (6:30 to 7:00 p.m.)
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56 The day-to-day learning procedure described in Chapter 2 was implemented within DYNASMART-P to model the ways in which drivers choose routes on a daily basis, as well as how they learn from previous travel experiences. The method establishes a minimum travel time improvement threshold, and drivers compare their default paths (originally based on minimum travel time)
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57 corridor can be created by aggregating one or more linkbased MOEs. Network-Level Performance Measures At the network level, DSP generates average travel time (minutes/veh)
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58 Regime II: Strategy Stabilization Period To test the effects of any type of network modification, the user must (a) allow drivers a sufficient number of learning days to adjust to the modified network and learn new paths as necessary before collecting statistics and (b)
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59 reversible-lane strategy was selected to demonstrate how to implement strategies in a DYNASMART-P network and what kind of results can be extracted from the simulation outputs. In order to measure the effects of the strategy, results from the baseline and strategy are compared.
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60 Network Performance: • Travel time * • Breakdown count *
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61 Table 4.6. Reversible-Lane Peak Daily Bottleneck Information (Freeway Corridor: Southbound)
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62 Thus, for this particular network, directional peaking along the freeway was not significant enough to warrant the removal of a lane from the off-peak direction to provide additional capacity to the peak direction. It should be noted, however, that the strategy did provided significant benefits to the peak direction, and for cases with lighter flow in the off-peak direction, or where the peak direction is highly critical for network performance, the strategy could have proved to be successful.
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63 and tested in DYNASMART-P. As depicted in the map in Figure 4.9, lanes were added on I-35 Southbound, the primary path for O-D pair 1-2.
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64 simulated for a total of 50 days. The results depicted in the following exhibits represent average values from Days 31 to 50 to take into account supply stochasticity.
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65 than lane mile addition Scenario A Error bars indicate that each of the strategies decreased the travel time variability for the primary O-D, indicating an overall increase in reliability.
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66 Limitations and Cautions The enhanced DTA model developed through this effort and described in the preceding chapters for a test network provides a practical methodology for assessing the ability of various operational strategies, either singly or in combination with one another, to forestall or eliminate the need to construct additional lane miles of capacity within a transportation network. The methodology provides effectiveness assessments about both travel time and reliability at the link, corridor, and network levels.
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67 stabilizes flow, lowers the probability of breakdown during demand surges, and reduces the potential for crashes. In this case, the benefit of ramp metering will be underestimated unless nonrecurring congestion effects are also considered.
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68 separate analyses of individual links, of separate corridors, and of the subarea network as a whole. The area is characterized by significant congestion on both freeway and arterial segments during typical weekday evening peak hours.
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69 subarea with more than 200 traffic analysis zones (TAZs) and more than 200,000 originating vehicle trips during the 4-hour weekday time period (3 p.m.
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70 demonstrate the new methods and model capabilities. Thus, for example, the number of through lanes on some arterials was modified, as was the length of some left and right turn pockets.
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71 switch. For this application, the percentage of drivers who could make a change in any given day was set to 15%, reflecting the reality that many people are creatures of habit and unlikely to make route changes right away, if ever.
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72 Measures of Effectiveness For the purposes of this demonstration project, a number of performance measures were monitored. Summary results for each performance measure were aggregated on a link, corridor, O-D-pair, and/or network basis, depending on the nature of the performance measure.
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73 Boulevard, resulting in four through lanes in each direction of travel; 3. Conversion of TV Highway west of Murray Boulevard from the existing five-lane cross section to a new sevenlane cross section through use of narrower lanes and shoulders; 4.
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74 27.5 28 28.5 29 29.5 30 30.5 31 1 Tr a ve lT im e (m inu tes ) Scenarios TV Hwy Travel Times (WB - 217 to Hillsboro)
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75 Cong. Pricing + imp.
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76 0 5 10 15 20 25 30 Baseline Rd Travel Time 1 Tr a ve lT im e (m inu tes ) Scenarios 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 Baseline Rd VMT 1 VM T Scenarios 0 2 4 6 8 10 12 14 16 18 20 Baseline Rd Density D en si ty (ve h/m i/ln )
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77 Imp Signal + cong Pricing New const Narrow lanes Imp Signal Imp sign + new lanes Pretrip Baseline (Rd) Imp Exist cond Exist (2 in TV)
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78 of course, but these by themselves do not provide a complete or even adequate assessment of an operational improvement strategy, particularly in situations where a range of improvement strategies is being tested.
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