What are the ‘Auto-Calculate’ and ‘Force Calculations’ icons used for?
Auto-Calculate is the default behavior for all HCS modules, including Streets. When Auto-Calculate is enabled, output values in the report are updated dynamically with each change to the input data. Streets is the only HCS module that allows Auto-Calculate to be turned off by the user, because the Streets calculations are complex and sometimes time-consuming on the computer. When the dataset has a large number of intersections and/or time periods, or when a slow computer is being used, the program sometimes needs several seconds to re-calculate. Turning off the Auto-Calculate feature allows the user to perform data entry more quickly, because the program will never pause to perform calculations. Once the data entry process is complete, the user can select either Auto-Calculate or Force Calculations. Both of these options will refresh output data in the reports, but only Force Calculations will allow the dynamic calculations to remain disabled. The analyst can use Auto-Calculate and Force Calculations in whatever way is most efficient for the size of their dataset and/or speed of their computer.
Why do the reports look disabled or grayed out? Why does ‘Phasing View’ look disabled or grayed out?
When the Auto-Calculate feature is turned off, output data are no longer updated in response to input data changes. This leads to situations in which output data will no longer be consistent with input data. The ‘stale feature’ (disabling or graying out) is used to notify the analyst that the output data are no longer up-to-date. This output data may include any of the formatted reports and text reports, and may include signal timings displayed by Phasing View. As soon as the user clicks on Auto-Calculate or Force Calculations, all outputs will be refreshed and the stale appearance will go away.
How do I code phasing?
The signal phasing sequence is specified by clicking on the Quick Phases dual-ring (NEMA) phasing diagram (phases 1 through 8). Only left-turn phasing needs to be specified, because thru movements and right-turn movements are automatically added to the phasing sequence as a function of laneage. Left-turn movements in odd-numbered phases are used to reflect protected left-turns (i.e., ‘green arrow’), whereas left-turn movements in even-numbered phases are used to reflect permitted left-turns (i.e., ‘green ball’). When exclusive right-turn lanes exist, shielded right-turns may be added by clicking twice on the corresponding odd-numbered phase. After the signal phasing and timing are entered a sequential phasing diagram (labeled ‘Phasing View’) will display the overall timing plan in an equivalent ‘single-ring’ format equivalent to how phasing was coded in previous versions.
What do the green times in Phasing View represent?
After the signal phasing and timing are entered, the Phasing View diagram displays the overall timing plan in an equivalent “single-ring” format. The HCM2010 procedure to calculate the average duration of an actuated phase generates the green times in the Phasing View. This procedure is used for estimating the average phase duration for an intersection that is operating with actuated control. Where appropriate, the description is extended to include techniques for estimating the duration of non-coordinated and coordinated phases. For pre-timed signals (Recall Mode set to Max for each phase), phase durations will usually reflect user-specified maximum green times. Alternatively, phase durations may be taken directly from user-entered data, by turning on the checkbox called Field-Measured Phase Times.
What is the difference between Demand used instead of Volume in Signals?
Demand is the arrival rate and Volume is usually taken to mean stop bar counts. Stop bar counts do not represent demand for congested conditions. In Signals, this plays a significant role in the determination of residual queues that are used to compute diod is essen delay. Counting the remaining queue at the end of each period is essential for determining total demand for every movement and period. For oversaturated situations, this can make a very significant difference in the computation of overall delays and level of service.
Why is there only one Peak Hour Factor field?
The Peak Hour Factor (PHF) specifies the proportion of peak-hour volume occurring in the peak 15 minutes for the entire intersection as prescribed by the HCM2010 for planning purposes. Peak 15-minute volume is computed as the hourly volume divided by four times the PHF. For operational applications, a multiple-period analysis using 15-minute Demands directly should be used which precludes the need for the PHF entirely.
What is the advantage in running a Multiple-Period analysis in Signals?
The HCM2010 states that for operational analyses, demand flow rates for each analysis period be provided. This is usually multiple periods to span the time normally needed for analyzing the peak hour(s). A multiple-period analysis can model the unmet demand that may exist from one 15-minute period to the next in oversaturated conditions. This analysis will estimate the residual queues for each period and use them as the initial queues for the subsequent period for each lane group. This will allow for a more accurate computation of additional delays (d3) attributable to these queues for the overall analysis period. This type of analysis should include under-saturated conditions for at least the first and last periods. Running a multiple-period analysis for any situation (including under-saturated conditions) also overcomes the dilemma in using the appropriate 15-minute period versus a peak-hour factor (PHF) that could vary among movements and periods.
What other requirements are there when collecting data for a Signals analysis?
There are several types of information required for a Signal analysis that can be obtained while performing turning movement counts: Residual queues (see above) for each period for all approaches; parking maneuvers per hour within 250 ft. of the stop bar; heavy vehicle percentages by movement; buses stopping per hour within 250 ft. (near side or far side); unequal lane distribution for a multiple lane movement; and right turns on red, pedestrians, and bicycles per hour on each approach.
What is the I-Factor in Signals and how is it computed?
The Upstream Filtering Adjustment Factor (I) accounts for the filtering effects of upstream signals within a mile of the analysis signal on each approach. It is based on the weighted average of the v/c ratios of the contributing movements from the upstream signal (automated in Signals) and can make a significant difference in the d approachin delay, especially where the subject approach has v/c ratios approaching or exceeding 1.0.
How are Arrival Type values in Signals determined?
Arrival type is used to describe the quality of signal progression for the corresponding movement group. Values of arrival type range from 1 to 6, with 1 representing poor progression, 6 representing exceptional progression, and 3 representing random vehicle arrivals. Typically, arrival type 3 is used for all uncoordinated, including actuated, movements and arrival type 4 is used for most coordinated movements.
What is the Queue Storage Ratio in Streets and is it important?
The Queue Storage Ratio (QSR) is the Maximum Back of Queue (HCM Chapter 16 Appendix G) divided by the Available Queue Storage Length. If the QSR is equal to or greater than 1.0, blockage will occur. The HCM procedures do not account for this blockage in the computation of delay and these situations must be simulated (with CORSIM) to get reasonable results.