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5 m/s intervals) and incorporates calibration parameters that reflect operating conditions, vehicle
[34]
specifications, and local environmental factors .
The MOBILE model, developed by the U.S. Environmental Protection Agency (EPA), follows a similar logic
[35]
to EMFAC but has not been updated since 2004 and does not include CO emission estimates .
2
Traffic situation models
Traffic situation models associate emission factors with specific driving conditions by analyzing real-world
vehicle operation patterns . These models typically classify traffic situations based on factors such as
[36]
region, road type, speed limit, and level of service, each corresponding to distinct emission factors . A
[37]
representative model is Handbook Emission Factors for Road Transport (HBEFA).

HBEFA is the standard model for road pollutant analysis in Germany, Switzerland, and Austria, and is
supported by the European Commission. It classifies emissions across multiple dimensions, including
[38]
emission types, vehicle categories, years, pollutants, traffic conditions, and road gradients . HBEFA also
provides part of the emission factor data used in the COPERT model .
[33]
To further clarify the similarities and differences among commonly used traditional emission models,
Table 2 presents a comparative summary of COPERT, EMFAC, MOBILE, and HBEFA in terms of their
input requirements, spatial and temporal resolution, supported vehicle and energy types, road categories,
and model versions.

Modal models
Modal models estimate vehicle emissions by segmenting vehicle operation into discrete modes defined by
parameters such as speed, acceleration, and engine revolutions per minute (RPM). Each mode corresponds
to an emission rate function that accounts for vehicle type, technology, and fuel characteristics. These
models operate at a high temporal resolution (1 Hz), enabling per-second estimation of vehicle modes and
their associated emission factors, which is why they are also referred to as instantaneous speed models .
[29]
Widely used modal models include Motor Vehicle Emission Simulator (MOVES), Comprehensive Modal
Emission Model (CMEM), and International Vehicle Emissions (IVE), along with various microscopic
emission models such as Passenger Car and Heavy-Duty Emission Model (PHEM) and Virginia Tech
microscopic energy and emission model (VT-Micro).

The MOVES model, developed by the U.S. EPA, is a comprehensive emission model that operates at macro,
meso, and micro levels. It characterizes emission rates from vehicles under different operating modes based
on Vehicle Specific Power (VSP) and vehicle speed bins. VSP represents the power demand imposed on the
engine to overcome all driving resistances, including grade resistance, aerodynamic drag, tire resistance, and
[39]
acceleration resistance . The MOVES model captures the emission performance of traffic flow on a given
road segment through the distribution of vehicle operating modes.

The IVE model, developed by the University of California, Riverside, aims to simulate motor vehicle
emissions in developing countries. It quantifies emissions based on VSP and engine load (ES) bins.

The CMEM model was sponsored by the National Cooperative Highway Research Program (NCHRP) and
the EPA. This model takes inputs such as acceleration, air/fuel equivalence ratio, fuel rate, speed, road
gradient, and auxiliary load. Data for modeling were collected by researchers using dynamometers, testing
[8]
300 real-world vehicles . The CMEM model consists of six main modules responsible for predicting engine