Page 2267 - trc_centennial_deir201705

12.0 Glossary

Particulate Matter, Respirable (PM10): PM10 is any particulate matter with an
aerodynamic diameter equal to or less than 10 microns (about /7 the diameter of a single
1
human hair). PM10 consists of particles directly emitted into the air and particulates formed
in the air from the chemical transformation of gaseous pollutants. PM10 particulates are
emitted from activities such as industrial and residential combustion, and from vehicle
exhaust. PM10 causes adverse health effects, atmospheric visibility reduction. It is a criteria
pollutant.

Parts Per Million (ppm): The number of weight or volume units of a minor constituent
present within each one million units of the major constituent of a solution or mixture, such
as salts in water.

PC: Passenger cars.

PC/H: Passenger cars per hour.

PC/H/LN: Passenger cars per hour per lane.

Passenger Trips: Relate to the volume of passenger service provided by public
transportation–such as buses, trains, and aircraft.

Passive Solar System: system that distributes collected heat via direct transfer from a
thermal mass rather than mechanical power. Passive systems rely on building design and
materials to collect and store heat and to create natural ventilation for cooling.

Peak Hour or Peak Period: The one hour period during which the roadway carries the
greatest number of vehicles. Traffic volumes are not constant throughout the day. Peak hours
are the times during which volumes are significantly higher than others. Most areas have two
peak hours–morning while people travel to work and late afternoon or evening as they leave
work and return home. In some cases as third, though usually smaller, peak occurs during
the middle of the day. As development intensifies and traffic volumes increase, the durations
of the peaks are extended until eventually the peak hour becomes a peak period which may
last for two or three hours. Peak period volumes are important as these are the times of day
when the most severe congestion occurs, and intersections must be designed to
accommodate these volumes if smooth traffic flow is to be maintained. The peak hour refers
to the one-hour period during the a.m. peak period (typically 7 AM to 9 AM) and the one-
hour period during the PM peak period (typically 3 PM to 6 PM) in which the greatest
number of vehicle trips are generated by a given land use or are traveling on a given roadway.

Percent Slope: A common way of expressing the steepness of the slope of terrain, which is
derived by dividing the change in elevation by the horizontal distance traversed. An increase
of 20 feet elevation over a 100 foot distance is a 20 percent slope.

Percent Variation in Travel Time: The RTP defines this as the day-to-day change in travel
times experienced by travelers. Variability results from accidents, weather, road closures,
system problems, and other non-recurrent conditions.

R:\Projects\PAS\CEN\000306\Draft EIR\12.0_Glossary-051017.docx 12-59 Centennial Project
Draft EIR