TEAPAC by Strong Concepts, HCM Watch

HCM Watch...

This page identifies specific issues we are aware of regarding the Highway Capacity Manual (HCM) published by the Transportation Research Board (TRB). For the most part information in this page will deal only with the Signalized Intersection methods of the HCM found in Chapters 10 and 16 of the HCM2000. Please be aware that this information is the best available at the time it is published, and the 2000 HCM has subsequently been updated in 2010 and 2016. The HCM Committee web page may also be another viable source for additional information related to the topics on this page, especially for pending and official 'interpretations' of the HCM procedures. An additional resource could be the TRB WebBoard discussion page for the HCM where HCM users discuss their experiences and questions about the Highway Capacity Manual. The address of these resource pages may change over time, so an internet search may be required to find their current location. 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 which optimizes signal timings and phasings for HCM capacity analyses explicitly follows the methods dictated by the HCM. 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.

Dennis Strong, President of Strong Concepts and author of TEAPAC, is a past Chairman of the Signals Subcommittee of the TRB Committee A3A10 which is responsible for the development and maintenance of the HCM.

2/12/02 - Queue Model Enhancement

At their January meeting, the HCM Capacity Committee approved several changes to the HCM signalized intersection queue model. Most notably, the method for handling unbalanced lane utilization has been improved from an approximation to a more precise calculation. Further, the original method allowed the calculation of an average lane queue, even when the saturation flow rate and delay calculations were based on unbalanced lane utilization -- this inconsistency has been removed. Lastly, the formula for the second term queue (Q2) was updated to include the effect that an initial queue has on this term. Check the HCM Committee web page for details about the changes made.

SIGNAL2000 has been updated to include these new changes in Version 1.11 which is downloadable as a free update for licensed SIGNAL2000 Ver 1.1x users. Ver 1.0x licenses must be updated for a fee of $69 (plus processing) which will include the new Ver 5 TEAPAC interface as part of the update.

2/22/01 - Queue Model Problems

It has been discovered that in the transcription of the underlying research which led to the new queue model in the HCM2000, the HCM2000 contractor omitted a number of critical constraints which must be applied when making the computations of that model. Not using these constraints can lead to irrational results, including extremely large queue values and even negatvie queues. In SIGNAL2000, these missing contraints can also lead to program crashes. The changes primarily affect computations when the arrival type is not 3 and/or when conditions are oversaturated, although other conditions may be affected as well. The Signals Subcommittee has approved the addition of these constraints to the HCM procedures and the HCM Committee is in the process of executing their official approval process. In the meantime, SIGNAL2000 has been updated to include these new constraints in Version 1.01 which is downloadable as a free update for licensed SIGNAL2000 users.

this page last updated April 15, 2019