An enhanced version of CAL3QHC, this model can process up to a year of hourly meteorological data and vehicular emissions, traffic volume, and signalization (ETS) data for each hour of a week.

vehicular emissionstraffic volumesignalization



Initial contribute: 2019-10-14


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Application-focused categoriesNatural-perspectiveAtmospheric regions

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The first CALINE line model was initially developed in 1972, with a focus on predicting CO concentrations near roadways (Benson, 1992). CALINE2 was developed in 1975, porting CALINE to FORTRAN and adding formulations for depressed roadways (Benson, 1992). CALINE3, which was developed in 1979 (Benson, 1979), updated the vertical and horizontal dispersion curves, reducing, but not eliminating, the overpredictions occasionally seen in CALINE2 (Benson, 1992). CALINE3 also updated the available averaging time, parameterized vehicle-induced turbulence, replaced the virtual point source with a finite line source, and increased the number of links capable in the model. CALINE3 was replaced by CALINE4 in 1984 (Benson, 1984), with further modifications to the lateral plume spread and vehicle induced turbulence, the addition of intersections, and limited chemistry for NO2 and PM. Unlike CALINE3, CALINE4 is not open source, such that the model code is not publically available, and thus does not meet the requirements in Appendix W for consideration as a preferred model. The CALINE models are Gaussian plume models, and though changes were made to the dispersion curves with each version, the dispersion curves are based on the Pasquill-Gifford (P-G) stability classes. The P-G stability classes do not reflect state of the science: the ISC dispersion model was also based on the P-G stability classes, and EPA replaced the ISC model with AERMOD in EPA’s 2005 revision to Appendix W. Section 2.2 includes additional detail about how stability is defined in AERMOD. 


In the late 1980s, CALINE3 was modified to automate estimates of vehicle queue lengths at intersections, resulting in the CAL3QHC screening model (U. S. EPA, 1995). In the early 1990s, further modifications were made to CAL3QHC to update traffic queuing and signaling based on the 1985 Highway Capacity Manual, increasing the number of links and receptors, and to add multiple wind directions to facilitate screening analyses (U. S. EPA, 1995). CAL3QHC was developed primarily for CO hot-spot analyses, computing hourly concentrations using “worse case” meteorology, which can then be scaled to an 8-hour average to estimate compliance with the CO National Ambient Air Quality Standard (NAAQS)


Shortly after the development of CAL3QHC, additional work was done with the model to allow more refined estimates (rather than screening estimates) of emissions from roadways. The CAL3QHCR model is based on CAL3QHC, but has several modifications, including the ability to run 1-year of hourly meteorology, additional capabilities related to queuing and signalization, the addition of PM to the hardcoded pollutant options, incorporation of the mixing height algorithms from ISCST2, the ability to vary emissions by hour of the week, and the ability to calculate averages longer than 1-hour (Eckhoff & Braverman, 1995). The model was developed for situations when the screening, worst-case estimates from CAL3QHC indicated potential exceedances of the standard and more refined estimates were required. It should be noted that with the incorporation of the ISCST2 mixing height algorithms, CAL3QHCR has undergone modifications from the dispersion in CALINE3 and CAL3QHCR that have not been reviewed with the same rigor and detail that was conducted for the other two models (Eckhoff & Braverman, 1995). As a result, there is some question as to the equivalency of CAL3QHCR to CALINE3 and CAL3QHC for identical model scenarios. Even so, CAL3QHCR has been listed in text of Appendix W, but not as a preferred model in Appendix A. CALINE3 was originally developed jointly by the Federal Highway Administration (FHWA) and the CA Department of Transportation (Caltrans). EPA sponsored much of the work to develop CAL3QHC and CAL3QHCR in the 1990s. The model codes are hosted on EPA’s dispersion model website



U.S. Environmental Protection Agency (2019). CAL3QHCR, Model Item, OpenGMS,


Initial contribute : 2019-10-14



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