## Appendix C

Proposed Method to Improve Temporal Distribution

Of Gridded On-road Motor Vehicle Emissions

Background

This document discusses a proposed method to improv e the temporal resolution of gridded on-road motor vehicle emission inventori es. The Integrated Transportation Network (ITN) and the Direct Travel Impact Model (DTIM) are currently used to develop the hourly, spatial distr ibution of on-road emissions. The ITN is a seamless on-road transportation networ k for California that contains about 250,000 roadway segments (or ‘links’). A rev ision to the ITN, called ITNv2, has recently been completed. The ITNv2, like the o riginal ITN, is developed from the transportation networks of several regional tra nsportation planning agencies (RTPAs) as well as the California Department of Tra nsportation’s (Caltrans) statewide model. The hourly emission maps produced from the ITNv2 and DTIM are used as spatial surrogates to map the county em ission estimates produced from ARB’s on-road motor vehicle emission model, EM FAC.

Travel activity data used in the ITNv2 represent tr avel during the core weekdays, Tuesday, Wednesday and Thursday. We do not propose to make adjustments to the hourly emissions of light or medium duty vehicl es produced by ITNv2/DTIM/EMFAC for these core days. However, (ex cept for southern California) hourly distributions of heavy-duty vehi cles are made by ratios of light duty travel. Therefore, we propose to use count dat a, which is distinguished by the vehicle type and number of axles, to temporally redistribute heavy-duty vehicle activity for all days, and light and medium duty vehicles for all non-core days. We place a special emphasis on weekend days since many pollutant episodes contain one or more weekend days.

In previous modeling work for CCOS using the first version of the ITN, adjustment factors were applied to approximate trav el on weekend days by lowering the volume on weekend days. This adjustme nt was based on a traffic study conducted by UC Davis for CCOS. See the desc ription of the previous methodology at the end of this document. Heavy dut y NOx emissions were

further reduced to reflect lowered weekend truck tr avel. However, all vehicle types were assigned the same diurnal patterns. Thi s is of concern because

trucks are known to have different diurnal distribu tions than cars and they have high NOx emissions.

Due to this concern, the Weekend Truck Subcommittee of the northern California SIP Gridded Inventory Coordination Group (GICG) was formed to investigate a way to improve day-of-week adjustments, for vehicle types as needed, but particularly for heavy-duty trucks. Participants i n the subcommittee are membersof the GICG with particular knowledge and/or intere st in improving the

adjustment factors and include representatives from Caltrans, ARB, Bay Area AQMD, San Joaquin Valley Unified APCD and Alpine Ge ophysics (the developer of the ITN). Since Caltrans count data are availab le to improve the temporal distribution of emissions by vehicle type, the UC D avis adjustments will not be

used in the ITNv2.

As a note of interest, while we are proposing ways of improving the temporal distribution of emissions, the spatial distribution is only altered at the county level. One way to correct the spatial distribution of on-r oad motor vehicle emissions on weekend days is through the development of a weeken d travel demand model. Some states have begun to investigate the developme nt of a weekend travel demand model; we are unaware of any such pursuit in California largely due to high cost of developing a weekend model.

Description of Current Work

Leonard Seitz of Caltrans acquired Automatic Vehicl e Classifier (AVC) count data from Joe Avis in Caltrans Traffic Ops from man y (~139) sites in the state for calendar year 2004 (see Figure 1). Caltrans staff prepared hourly day of week factors for (1) passenger cars (LD), (2) light and medium duty trucks (LM), and (3) heavy-heavy duty trucks (HHDT). Caltrans count data are separated using the Federal Highway Administration (FHWA) vehicle c lassification scheme (see Table 1). Passenger cars are defined as FHWA class es 1 through 3. Light and medium heavy duty trucks are defined as FHWA classe s 7 and 8. Heavy-heavy duty trucks are defined as FHWA classes 9 through 1 4. Separate factors were prepared for each Caltrans District. One or more c ounties may fall into a single

District. All counties within each Caltrans distri ct will receive the same adjustment. Figure 2 shows a map of county and Cal trans district. Only counts during the summer of 2004 were used, specifically t he months of June, July and August excluding data from July 2-5 to remove unusu al traffic patterns around the July 4 th holiday.

Proposed Method

Temporal on-road activity adjustments by county wil l be made for:

1. Heavy duty vehicles – all days 2. Light duty vehicles – Friday, Saturday, Sunday, Monday

Daily total activity (daily VMT) adjustments will b e made for all vehicle types for Friday, Saturday, Sunday, and Monday. Tuesday, Wed nesday and Thursday are considered as one day. Adjustments applied to heav y-duty vehicles on Tuesdays, Wednesdays and Thursdays will be the same for each of the three days.Since it is EMFAC emission estimates that are being adjusted to derive the final

on-road inventory, the relation between EMFAC vehic le classes and Caltrans’ adjustment factors is shown here.

EMFAC Class Description Caltrans’ Factor

1 LDA LD

2 LDT1 LD

3 LDT2 LD

4 MDV LD

5 LHDT1 LM

6 LHDT2 LM

7 MHDT LM

8 HHDT HHDT

9 Other Bus No data in ITNv2 10 School Bus Unadjusted on weekdays, zero on weekend days

11 Urban Bus LD

12 Motorhomes LD 13 Motorcycles LD

where LD based on count data for FhwA classes 1 thr ough 3

LM based on count data for FhwA classes 7 and 8

HHDT based on count data for FhwA classes 9 throu gh 14

Here are the proposed steps for the adjustments:

1) Sum the hourly volumes by vehicle type and county o n the ITNv2 network.

2) For heavy-duty core days there will be an hourly redistribution but no daily VMT adjustment. Light duty vehicle emissions from EMFAC will not be adjusted at all for core days.

3) For Friday, Saturday, Sunday, and Monday, develo p a set of ratios of Caltrans daily VMT to core days. That is, for Satur day to Tues-Thurs (etc), by Caltrans 3 factor types LD, LM and HHDT.

4) Apply Caltrans daily factors by county, and seco ndly, apply Caltrans’ new hourly distributions by county to ITNv2 link activi ty.

5) Run DTIM with revised ITNv2 activity.

6) Run EMFAC with day specific temperatures.

7) Adjust DTIM output emissions to EMFAC weekday by county.8) For Friday, Saturday, Sunday, and Monday, apply daily ratios from step 3 to hourly DTIM emissions by county.

To summarize, for core days light- and medium-duty vehicle emissions will equal EMFAC emissions by county and hour. For core days, heavy-duty emissions will equal EMFAC but have Caltrans hourly distribution.

For Friday through Monday, EMFAC weekday emissions will be scaled to reflect Caltrans day of week factors.

Previous Method for Making Weekend Adjustments

EMFAC does not make weekend day estimates, so EMFAC daily emissions were scaled to represent weekend estimates based upon av ailable traffic count data. The ITN version 1 network has activity estimates fo r a weekend day. In order to approximate an EMFAC weekend day inventory, ARB sta ff scaled each county’s EMFAC pollutants, except NOx, by the ratio of ITN V MT for a weekend day divided by the ITN VMT for a weekday for each count y. The VMT for a weekend day was determined based on vehicle counts gathered and analyzed by Dr. Deb Neimeier of UC Davis. The county-specific ratio was applied to all vehicle classes and pollutants, except for NOx emissions from heavy -duty diesel trucks. Since heavy-duty diesel VMT is drastically reduced on wee kends and NOx emissions from heavy-duty trucks are large, ARB staff multipl ied the weekday NOx emissions by a factor of 0.536 (reduction of 46.4%) to estimate the NOx emissions on a weekend day. The factor of 0.536 re presents the average reduction in NOx for a weekend day in the South Coa st Air Basin. This NOx reduction was derived from Caltrans Weigh-in-Motion traffic counts that can differentiate between vehicle types by weight.Figure 1 Caltrans Weigh-In-Motion Data SitesTable 1 Federal Highway Administration (FHwA) Vehi cle Classification

Graphic Depiction FHWA

Class Description

1 Motorcycles

2 Passenger Cars (With 1- or 2-Axle Trailers)

3 2 Axles, 4-Tire Single Units, Pickup or Van (With 1- or 2-Axle Trailers)

4 Buses

5 2D - 2 Axles, 6- Tire Single Units (Includes Handicappe-Equipped Bus and Mini School Bus)

6 3 Axles, Single Unit

7 4 or More Axles, Single

Unit

8 3 to 4 Axles, Single TrailerGraphic Depiction FHWA

Class Description

9 5 Axles, Single Trailer

10 6 or More Axles, Single

Trailer

11 5 or Less Axles, MultiTrailers

12 6 Axles, Multi-Trailers

13 7 Axles, Multi-Trailers

No graphic available 14 5 Axles: 3 axle tractor pulling a 2 axle trailer (FHWA considers this type
of truck a class 9;Caltrans

counts these trucks separately for operational purposes.)Figure 2 Caltrans District and County Boundaries