HCS Watch...

This page identifies specific issues we are aware of regarding the HCS and HCS2000 software published by the McTrans Center. For the most part this will deal only with the Signalized Intersection module of HCS. Please be aware that this information is the best available at the time it is published, and may not be accurate for recently released versions, which has subsequently been updated since HCS2000. You might also check our User Discussion Forum for questions and discussions which may also be helpful.

This page is relevant to TEAPAC software users because the SIGNAL function of TEAPAC which optimizes signal timings and phasings for HCM capacity analyses performs the same capacity analyses as the Signalized Intersection module of HCS, and thus should produce the same capacity analysis results. In addition, the HCM saturation flows computed by the SIGNAL function (as well as the optimized timings and phasings) can be used directly by other TEAPAC functions, such as PRETRANSYT which creates data files for the TRANSYT program, PRENETSIM which prepares input files for CORSIM, PREPASSR which prepares input files for PASSER-II, PRETSPPD which prepares input files for TS/PP-DRAFT, and PRESYNCHRO which prepares input files for SYNCHRO/SIMTRAFFIC.

4/27/06 - Unopposed Left Turn Does Not Properly Reflect Pedestrian Interference (Ver 4.1f)

When a left turn has no opposing through volume, it should use a left turn adjustment factor of 0.95, but the pedestrian interference factor used should reflect the effect that the opposing ped volume has on the left turn movement.  HCS2000 does not take this effect into account and always uses a ped interference factor of 1.00.

6/14/05 - Leaving All-Red Input Blank Causes Erroneous Results (Ver 4.1e)

When entering a new problem into HCS2000, it has been observed that if an actual entry is not made for the all-red time of a phase, calculated delay values may not be correct.  That is to say, if the all-red time is left blank, a different delay value may be calculated vs. entering 0 for the all-red time.

5/26/05 - Protected-Permitted Left Turn Delay Overestimated (Ver 4.1e)

When calculating the delay for a protected-permitted left turn, under certain circumstances HCS2000 will mis-calculate the delay, as follows. In cases where the protected and permitted phases are immediately adjacent to each other in the phasing, the HCM dictates that only the first phase should have lost time applied when determining the effective green time, and the second phase should not have any lost time applied. It has been observed that in some cases, some indeterminate amount of lost time will be applied to the second phase by HCS2000, thereby invalidating the results.

8/1/04 - Permitted Left Turn Worksheet Selection Corrected in Ver 4.1e

Release 4.1e is primarily to respond to an issue with the permitted left-turn worksheet selection process in Signals. The update will ensure the correct permitted left-turn worksheet is selected in all lane configuration cases and identify whether the HCM 2000 Supplemental Worksheet for Permitted Left Turns Opposed by a Single- or Multilane- Approach as "S" or "M" in the Text Report for each approach. This update also corrects the calculation of minimum pedestrian green times (Signals) in some Metric files.

4/11/02 - Protected-Permitted Left Turn Queues Underestimated (Ver 4.1b)

When calculating the queue length for a protected-permitted left turn, HCS2000 will underestimate the queue length, as follows. The green time used in the calculations is the entire green time for both the protected and permitted phases, as it should be, but the saturation flow rate used is the rate determined for the protected phase only. This causes the queue model to release vehicles during the permitted phase at a rate usually much higher than the saturation flow determined for the permitted phase, thus reducing the maximum extent of the back of queue. Since the queue model is founded on a single period of green display, a more appropriate result would be achieved by calculating the average saturation flow rate during the combined protected-permitted green time and using this in the calculations (this is equivalent in concept to the averaging method for saturation flow determination for the various green portions of a permitted phase in Appendix C). This is the method followed by the SIGNAL2000 program.

3/22/00 - Heavy Vehicle Factor Computed Wrong (Ver 3.1c)

For a lane group with volumes from more than one movement, HCS will allow you to enter heavy vehicle percentages for all of the movements (as it should), but only the percentage for the 'primary' movement of the lane group will be used to compute the heavy vehicle adjustment factor. For example, if right turns are included in a through lane group, HCS will allow you to enter a percentage of heavy vehicles for the right turns, but this percentage is ignored, regardless of its value. A proper analysis calculates the weighted average heavy vehicle percentage for all movements in the lane group and uses this percentage to calculate the heavy vehicle adjustment factor. For example, a through lane group with 50 through vehclees and 50 right turns has a total of 100 vehicles. If the through movement has 50% trucks (25 trucks) and the right turns have 0% trucks, there are 25 trucks in the lane group. This is 25% heavy vehicles which should result in an adjustment factor of 0.800. HCS will use only the 50% trucks for the through movement, resulting in an adjustment factor of 0.667. This problem was apparently corrected in Ver 3.2, but not confirmed by this reviewer.

3/22/00 - Defacto Left Turn Analysis Wrong for Shared-Lane, Protected-Permitted Analysis (Ver 3.1c)

A shared-lane, protected-permitted left-turn condition is Case 6 in Table 9-12 of the HCM. Case 6 uses a single formula to estimate the effect of left turns on the shared lane group. This formula does not include an estimate of the proportion of left turns in the left lane, and as a result does not include a defacto left turn check based on that proportion. Thus, Case 6 cannot generate a defacto left turn analysis. HCS will conduct such an erroneous defacto left turn check for a Case 6 condition, and as a result may produce a defacto left turn analysis which is not appropriate. This problem was apparently corrected in Ver 3.2, but not confirmed by this reviewer.

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this page last updated April 15, 2019