Model Change Bulletin

                                    MCB#1                        06/01/93

                            CAL3QHC (dated 93157)


     This Model Change Bulletin initiates the use of the CAL3QHC (dated 93157)
model.  The principal difference between the original CAL3QHC model, released
in August 1990, and this revised CAL3QHC (dated 93157) pertains to the
calculation of intersection capacity, vehicle delay, and queue length.  This
update includes three new traffic parameters that can be optionally specified
by the user:  Saturation Flow Rate, Signal Type, and Arrival Type.  These
parameters permit more precise specification of the operational characteristics
of an intersection than in the original CAL3QHC model.  If these parameters are
not specified by the user, the model defaults to a saturation flow rate of 1600
vph/lane, pretimed signal type, and a progression that assumes random arrivals
(these values are representative of typical urban intersections).  The
"stopped" delay (used in the queue calculation) was replaced  with "approach"
delay following recommendations from the 1985 Highway Capacity Manual.

     CAL3QHC (dated 93157) has been expanded to accomodate up to 120 roadway
links, 60 receptor locations, and 360 wind angles, an increase from the
original version which could accommodate 55 links and 20 receptors.  This
allows the modeling of adjacent intersections that interact with each other
within a short distance.

     This revised CAL3QHC model contains the same input format as the original
version, with the only exception that the idle emission factor must be input
in "grams per hour" instead of the original "grams per minute".  The ouput
format has been expanded to provide all the input queue and emission
parameters for verification purpose, and the option to be printed in either
Metric or English units has been added.

     The User's Guide to CAL3QHC has been revised to provide all the
information necessary to run CAL3QHC (dated 93157).