Matthew Rodriquez 

Secretary for 

Environmental Protection 

December 3, 2014 

Matthew Spears 

Center Director 

Air Resources Board 

Mary D. Nichols, Chairman 

9480 Telstar Avenue, Suite 4 

El Monte, California 91731 • www.arb.ca.gov 

U.S. Environmental Protection Agency 

2000 Traverwood Drive 

Ann Arbor, Michigan 48105 

Dear Mr. Spears: 

Edmund G. Brown Jr. 

Governor 

Thank you for the opportunity to assist with the development of the Phase 2 greenhouse 

gas regulations for heavy-duty vehicles. Air Resources Board staff has prepared the 

enclosed assessment of the potential use of credits for solar reflective paint and solar 

control glazing for these vehicle classes. To summarize, staff recommends that no 

credit be offered for solar reflective paint because such paint would not result in 

significant benefits for heavy-duty vehicles, and recommends a methodology to 

determine credits for solar control glazing. 

If you have any comments or questions, please contact Ms. Kim Heroy-Rogalski, 

Manager, Strategic Planning and Development Section, at (916) 327-2200 or by email 

at kheroyro@arb.ca.gov. 

Sincerely, 

Michael Carter, Chief 

Mobile Source Regulatory Development Branch 

Enclosure 

cc: James Tamm, Chief 

Fuel Economy Division 

National Highway Traffic Safety Administration 

1200 New Jersey Avenue, SE 

Washington, DC 20590 

Kim Heroy-Rogalski, Manager 

Strategic Planning and Development Section 

\ 

The energy challenge facing California is real. Every Californian needs to take immediate action to reduce energy consumption. 

For a list of simple ways you can reduce demand and cut your energy costs, see our website: http://www.arb.ca.gov. 

California Environmental Protection Agency 

Printed on Recycled Paper 
Executive Summary 

Solar Control: Heavy-Duty Vehicles 

A White Paper 

October 30, 2014 

Solar reflective paint and solar control glazing can reduce the interior temperature in a 

vehicle, thereby reducing the air conditioning requirements, and thus reducing fuel 

consumption. The Low Emission Vehicle Ill Regulations (LEVIII) include a greenhouse 

gas (GHG) credit for this benefit, which is generally not reflected in emissions tests. 

The credit is based on the premise that the air conditioner can be downsized due to 

reduced energy demands. This paper presents a brief discussion of the potential use of 

such credits for heavy-duty vehicles. Credits have been suggested by the Enhanced 

Protective Glass Automotive Association (EPGAA) for solar control glazing to credit 

emission reductions for both the portion of time these vehicles are driven and the 

portion of time they are idled. Air Resources Board (ARB) staff believe a credit for the 

brief idle time portion of the duty cycle is appropriate. This credit must be adjusted for a 

variety of factors such as insolation rate, daytime idling, and other technological factors. 

Staff does not believe it is appropriate to include a credit for drive time. Staff also does 

not believe credits for solar reflective paint are appropriate. Section I of this paper 

addresses the thermal control credits available in ARB's LEVIII regulation. Section II 

notes potential benefits from solar control paint and glazing. Finally, Section Ill provides 

suggestions and recommendations. 

I. Thermal Control Credits in Light-Duty Vehicles 

In its LEV Ill regulations, ARB included credits for thermal comfort systems for \ 

passenger cars as well as light duty trucks (LOT) and medium duty passenger vehicles 

(MDPV). These have been adopted by the United States Environmental Protection 

Agency (EPA) as well. The passenger car credits are accrued through th~~use of solar / 

control glazing (no more than 2.9 gram per mile carbon dioxide (g/mi C02)), various 

ventilation approaches (credit of 1.0 - 2.1 g/mi C02), and solar reflective paint (0.4 g/mi 

C02). Similar though slightly higher credits are available for the other affected vehicles. 

A total thermal comfort credit of 3.0 g/mi C02 is available for passenger cars, and 4.3 

g/mi for LOTs and MDPVs. These thermal credits account for up to 2.1 percent of 

assumed GHG for advanced vehicles. The credits are based on the fact that the use of 

these approaches reduces the solar load while the vehicle is parked, which results in 

reduced cooling demand on the air conditioner, which enables the air conditioner to be 

downsized, thus reducing fuel use while driving. (Air conditioners for the passenger 

market are sized to allow the rapid cool-down of a car that has been parked in the sun, 

1 
so a less hot internal temperature means less cooling needs be accomplished to 

achieve desired interior temperatures.) 

II. Solar Reflective Paint and Solar Control Glazing for Heavy-Duty Trucks 

A. Solar Reflective Paint 

Sunlight that strikes a vehicle is composed of a mix primarily of visible and infrared 

(heat) wavelengths. Solar reflective paints reflect the infrared portion of the solar 

spectrum, which contains about half of the total energy, while minimally affecting the 

visible light portion, so that perceived color remains unchanged. In 2008, the National 

Renewable Energy Laboratory (NREL) noted that for sleeper cabs, solar reflective paint 

resulted in a greater thermal benefit than for light-duty vehicles due to the greater 

proportion of paint to glass in the heavy-duty sector (Rugh, 2008). Lustbader (2014) 

concluded that electric air conditioner loads in sleeper cabs can be reduced by nearly 

21 percent with a switch from black to white paint, corresponding to a 16.7 percent 

reduction in air conditioner battery capacity and a 48 pound weight reduction from the 

standard battery size. Lesser, though still significant reductions can be had while 

maintaining existing paint colors through the use of paints formulated to reflect the 

infrared ·wavelengths while maintaining the original visible color .. 

There are no current efforts to use solar reflective paints in the heavy-duty market, 

although a relatively large percentage of trucks are white, which typically reflect around 

70 percent of the total solar spectrum. As a point of reference, most black paint reflects 

around 5 percent, while a color-matched solar reflective black paint might reflect 30 

percent of the sun's energy, since the visible light must still be absorbed. 

B. Solar Control Glazing \ 

When sunlight impacts the glazing of a vehicle, some of the energy reflects off the 

glazing, some is absorbed by the glazing, and some penetrates through the ~lazing. 

The energy that ultimately makes it through the glazing, including that rera9iated from 

the absorbed portion, is called the total solar transmittance (known as TTS). That 

energy is then retained in the vehicle, much like occurs in a greenhouse. Currently, the 

windshields of most heavy-duty trucks use solar absorbing glass. This glass absorbs 

~he infrared heat energy. Ultimately, that heat energy is reradiated either into the cab or 

lost to the environment. The proportions depend primarily on the relative temperatures 

and wind flow. 

The use of optimized solar control glazing for heavy-duty vehicles was found to reduce 

the interior temperature of a parked truck by up to 5 degrees Celsius (Rugh, 2008). 

This reduction in the thermal load could make it feasible under certain conditions to shut 

down a truck that is being idled for cooling purposes. 

2 
C. Potential Benefit of Solar Reflective Paint and Solar Control Glazing 

Just as solar reflective paint and solar control glazing can reduce cooling demand in 

passenger cars, they can also reduce cooling demand in heavy-duty trucks. However, 

thermal comfort credits for heavy-duty vehicles need to be specific to the different 

characteristics of these vehicle classes. Heavy duty vehicles are operated in a different 

manner than passenger vehicles, and in fact, each class of heavy-duty vehicles may 

operate in a unique way. For example, class 8 line haul trucks may be legally driven up 

to 11 continuous hours in a 14 hour workday before a ten hour rest break is mandated. 

Much of the driving may occur during night-time hours when there is less congestion. 

Vocational trucks are more likely operated in urban situations, with many short stops 

throughout the work-day. These vehicles likely operate predominantly during daylight 

hours. Because the load from air conditioning is a small fraction of the available 

horsepower, use of the air conditioner has a minimal effect on fuel economy while 

driving under most duty cycles. 

However, heavy duty vehicles spend over 1,8001 hours per year idling while the 

vehicles are being loaded or unloaded, while queuing, and during mandated rest 

breaks. Often, the engine is idled simply to provide for driver comfort. 2 Since up to a 

gallon of fuel can be burned while idling per hour, rest period idling alone results in well 

over 800 million gallons per year of wasted fuel and associated emissions in the 

nationwide fleet. In some daytime situations, thermal comfort options such as solar 

control paint and glazing should enable the driver to shut off the engine during short 

driving breaks (30 min or less), such as for loading and unloading, during moderate 

ambient daytime conditions without the cab becoming uncomfortably warm. However, 

longer breaks will result in uncomfortably warm cabins during even moderately 

temperate days regardless of the thermal controls employed. 3 

\ 

It is difficult to assess the potential emission reductions if all heavy-duty trucks used the /,- highest level of solar control paint and glazing. This is due to a number of factors. 

Solar control promotes thermal comfort while driving and during rest breaks and other 

engine idle times. To the extent that the load on the engine is reduced during driving 

operation by the lower cooling demand and that load reduction corresponds to reduced 

emissions, there will be an emissions reduction benefit. However, the additional load on 

the engine from the air conditioner compressor in a large engine is less substantial than 

1 This com-mon estimate of idle time seems based on 6 hours idling per day, 300 days per year. It appears consistent 

with the findings from Lutsey et al's 2004 nationwide truck survey, who also noted that while approximately 75 

percent of survey respondents idled to provide heating or cooling, 35 percent also indicated they idle to power 

-accessories, 13 percent idled to avoid start-up problems, and 9 percent idled merely to drown out other noise. 

However, idling restrictions are becoming increasingly common. 2 Although anti-idling measures are in effect in California, vehicles meeting the clean idle standard are allowed to idle 

more than the 5 minutes otherwise allowed. Similar exemptions are in place nationwide for states that at least 

nominally prohibit idling. SeeATR12013. · 3 Consider how quickly the interior of a car parked in the sun will exceed 1 00 degrees Fahrenheit. 

3 
the load on a small engine. Further, technology continues to be developed to lessen 

the impact on emissions from air conditioner use, especially in this sector. When 

parked, newer trucks can use battery-powered thermal comfort systems, auxiliary power 

units, or electric hoteling where available. However, during loading/unloading 

operations and queuing, the idling engine will likely be providing the power for thermal 

comfort, and these technologies could result in emission reductions. 

1. Benefits of Solar Reflective Paint 

The potential emission benefit from a switch to solar reflective paint is difficult to 

quantify. First, one must account for the baseline color mix, which is biased towards 

white vehicles. Second, one must account for the fact that color-matched solar 

reflective paints remain much less reflective than white paint, as they must still absorb 

the visible light rays needed to produce the desired color. Third, solar reflective paints 

offer little or no benefit while the vehicle is in motion, since any heat buildup is lost 

external to the vehicle. Lustbader's reduction in the size of an electric system remains 

real, but the fuel economy benefit would seem to be derived from the small reduction in 

the needed battery pack weight, and even this is only achieved if the units are sized 

specific to the color of the vehicle. A black solar reflective chassis would still need 

substantially morl3 cooling capacity than a white chassis, and unless manufacturers size 

the unit to the color of the chassis, both colors will end up with the larger unit. 

2. Benefits of Solar Control Glazing 

According to EPGAA, most medium- and heavy-duty trucks are delivered with 

windshields having a TTS of around 58 percent. These windshields are frequently 

replaced; replacement windshields are typically also solar absorbing, but usually allow 

slightly more solar energy into the cab, with a TTS of around 62 percent, similar t~ that 

of automobile windshields. Solar control glazing is commercially available that transmits 

far less solar energy into the vehicle. A TTS somewhat above 40 percent is currently 

achievable, while still maintaining the 70 percent visible light transmittance that is 

required for vision glazing. Such glazing typically reflects most of the infra~ed rays 

(solar reflective4

), and can be ceramic- or metal-based. NREL's testing of a class 6 truck 

showed solar reflective glazing can reduce the interior temperatures after a hot soak by 

4. 7 C, resulting in a 0.2 mile per gallon(mpg) increase over a baseline of 11.3 mpg on 

the SC03 cycle, but no change in fuel economy over a constant 65 mph cycle. Again, 

the primary benefit is obtained when a vehicle is parked (off or idling). 

Gaines et al (2006) used the 2002 Vehicle Inventory and Use Survey data and other 

assumptions to estimate truck fleet idling, which has two components- rest period 

4 The infrared rays, not the visible light rays, are reflected. The glazing does not have a mirror finish. It visually 

appears much like non-solar reflective glazing. 

4 
idling and workday idling.5 The analysis concluded that nearly 700 million gallons of 

fuel were used for rest period idling for long-haul sleeper trucks and another 2.5 billion 

gallons of fuel were used for workday idling for various classes of heavy-duty trucks. 

What fraction of the associated idle time would potentially be reduced by solar control 

measures? In other words, what portion of total idle time occurs in increments of 30 

minutes or less during the day during times of the year when ambient temperatures 

would allow engines to be shut down without interior temperatures becoming 

excessively warm? There appear to be no strong data to answer these questions, so a 

number of assumptions will need to be made. These assumptions should be refined as 

data are obtained: 

• Thermal comfort measures will not reduce rest period idling time or emissions (with 

a caveat about potential weight savings for electric systems) because even the best 

thermal control systems are insufficient over the long term, and because rest-period 

options to idling already exist. 

• ARB has some limited data for Class 5-7 truck idling, showing that these vehicles 

tended to idle about 50 percent of the time that they were running each day.6 Linehaul trucks are reported to idle around 6 hours per day, be off for four hours per day, 

and therefore be driven 14 hours per day on average. This implies that 30 percent 

of the time the truck is on, it is idling. 

• ARB assumes that 25 percent of workday idling is queuing. While thermal controls 

may increase driver comfort during these periods, the engine generally remains on 

while in creep mode so that the truck can move with the queue. · 

• ARB assumes that 75 percent of workday idling is loading/unloading and short 

breaks (such as for meals). This is the potentially affected portion of total idle time. 

• Temperatures during winter and summer are too extreme to allow thermal comfort 

without some technology such as idling, heaters, or electric air conditioners. 

• Temperatures during spring and fall are sometimes suitable to allow thermal cqmfort 

approaches to eliminate the need for idling during short stops (maximum of 150 

driving days/year). Early mornings throughout the summer may be sufficiently cool to 

avoid a need for comfort idling during short stops, but the insolation rate/angle is low 

during these times, so solar controls will be of minimal benefit. 

• Stops of greater than 30 minutes will require heating or cooling for driver comfort 

even during moderate ambient conditions. (Note how quickly a parked car warms, 

5 Note that this figure is based on the 2002 Vehicle Inventory and Use Survey. Diesel fuel was substantially less 

expensive in that time period, on the order of $1.30 per gallon. It is possible that at today's diesel fuel prices, 

discretionary idling may have been substantially reduced. However, ARB is aware of no evidence to support such a 

supposition. 

6 As part of an NREL project being completed for ARB, a number of trucks were datalogged. Draft data for 46 

beverage delivery trucks (class 7 day cabs) from operations in Fresno, San Diego, Buena Park and Hayward, totaling 

approximately 810 total vehicle days of operation, showed that 63 percent of logged time was spent idling. 53 

percent of the time was spent idling by 31 linen delivery vehicles (class 6 step vans) operating in Sacramento, 

Pittsburg, Hayward, Novato, San Jose, Concord, Paramount, Riverside, Santa Ana and Sylmar for about 575 total 

vehicle days of operation, and 40 parcel delivery vehicles (class 5-6 step vans) operating in Aliso Viejo, Costa Mesa 

and Sun Valley over about 690 total vehicle days of operation were idled about 44 percent of the time. 

5 
even in the fall or spring.) ARB assumes that 50 percent ofstops are 30 minutes or 

more. 

• Seventy five (75) percent of respondents in a survey performed by researchers at 

the University of California, Davis, noted that they idled for thermal comfort. Thirty 

five (35) percent noted they idle to power accessories. Idling also occurs for other 

reasons in lesser percentages. Therefore, at most 65 percent of idling is solely for 

thermal comfort (Lutsey et al, 2004). ARB assumes idling for heating and cooling is 

evenly split nationalll, and that only idling for cooling is applicable here. In fact, the 

solar control glazing could increase the heating needs in the early mornings and 

throughout winter as more of the warming solar rays are excluded. 

• Since EPGAA reports truck glass is replaced as frequently as every six months, 

ARB assumes vision glazing has a TTS of 62 percent. Alternately, a discounted 

credit for the originally improved glazing could be incorporated. 

All of these factors must be considered for an idle credit for solar control glazing. Using 

these assumptions, 50 percent (of the time vehicles are idled)* 50 percent (of the year 

when conditions are moderate)* 75 percent (of the idling time that is for loading, 

unloading/meals)* 50 percent (of these stops are <30 minutes)* 65 percent (of the time 

the idling is for thermal comfort)* 50 percent (of the thermal comfort that is cooling) 

gives an applicable idling factor of 3 percent of the current engine operation time that 

could be reduced by thermal comfort's contribution to potential idle reduction. (In 

addition, not all idling occurs during the day, so the day/night correction factor discussed 

below must also be applied.) 

Ill. Proposals, Adjustments, and Recommendations 

A. Solar Reflective Paint 

Solar reflective paint has little or no benefit when a vehicle is in motion. However) if a 

credit for solar reflective paint is incorporated in the Phase 2 standards, ARB 

recommends adjusting the credit allowed in the light-duty rule (0.5 g/mi for light-duty 

trucks and medium-duty passenger vehicles) by a baseline paint color adjustment to 

reflect current estimates of the color mix (An estimated 30 percent of Class 7 and 8 

trucks are other than white or cream. 8

) as well as applicable factors discussed above 

and the percent of the idle time that occurs during sunlight hours, discussed in the 

glazing section below. Because the expected COz benefits of solar reflective paint on 

heavy-duty vehicles are expected to be insignificant compared to overall vehicle 

7 California's Emission FACtors (EMFAC2011) model assumes California summer (cooling) months are March 

through September and winter (heating) months are October through February, for a 58/42 percent split. 

respectively. 

8 Staffs nonscientific survey completed in 2009 in the Los Angeles area found that approximately 70 percent of class 

7 and 8 trucks operating on the freeways during rush hour are white. The non-white trucks were often part of a fleet, 

such as UPS, which specifies a particular paint color. 

6 
emissions, 9 ARB recommends that no credit for such paint be included in the Phase 2 

GHG regulation. 

B. Solar Control Glazing 

1. EPGAA Proposal for Driving and Idling Credits 

Two credits were proposed by EPGAA for solar reflective glazing. First, they suggest a 

credit to apply to the driving portion of the duty cycle, using the same formula as for the 

LOT segment, with units adjusted as appropriate for the heavy-duty fleet. Second, 

EPGAA suggests a separate idling credit. This would be a function of idle time, 

geographic location, TTS, and glazing area. It would use the base formula from the 

driving calculation which includes TTS and glazing area, possibly with an increased Zvalue 10 of 0.55 (vs. 0.4 for LOT), but with an adjustment for insolation rates (Much of the 

solar benefits work is completed at NREL's Golden, Colorado facility which may not 

have insolation rates typical of the national average.) and a multiplicand 10 , the fraction 

of the fleet that daytime idles, which they assumed equal to 0.7. It was acknowledged 

that this term needs refinement. 

2. Recommendations for Driving Credits 

EPGAA's recommendations were based on the light-duty vehicle thermal comfort 

credits included in LEVI! I. The gram per mile credits were extrapolated based on the 

amount of downsizing that would be made to an air conditioner due to reduced solar 

load while a vehicle was parked. Since emission tests obviously do not measure 

tailpipe emissions for cars that are not running, the benefit was manipulated into a form 

suitable to be applied as a credit to the driving cycle. For the LDV sector, air conditioner 

use results in a significant load on the engine, substantially reducing fuel economy. 

However, as the engine gets more powerful, the impact of this additional load beComes 

smaller, and a lesser effect is seen on fuel economy. Thus, the potential benefit to 

downsizing is reduced in engines of the sizes used in the heavy-duty fleet. In addition, 

the thermal benefit to solar control paint or glazing tends to be less substantial when 

driving, where more of the heat energy will desorb to the outside than to the inside due 

to air flow. Therefore, ARB believes that it is not appropriate to include a separate 

driving credit for solar control glazing in the Phase 2 GHG regulations. 

9 0.5 g/mi * 0.3 = 0.15 g/mile credit, ignoring all factors needed to limit benefits calculations to short-term daytime 

idling. ARB staff believe this is negligible (less than 0.01%) compared to the Phase 1 standard, which . 

translates to 2016 g/mi C02• 10 The Z-value represents the relationship between glazing performance and interior temperatures of a parked 

vehicle. 

7 
3. Recommendations for Idling Credits 

ARB believes a credit relating to the time the engine would have been idling to provide 

thermal comfort, but instead can be shut down, is appropriate. Note that due to the 

limited applicability times, as discussed above, this credit will be small. Any credits 

must be crafted to ensure that manufacturers are not taking credit for existing actions. 

For example, EPGAA proposed a baseline TTS for glazing of 62 percent, based on the 

TTS of typical replacement glass. However, EPGAA also noted that the glazing 

installed by manufacturers is often closer to 58 or 59 percent TTS. If a credit were to be 

granted based on the higher replacement TTS, the manufacturers would receive a de 

facto credit. An overly generous credit could actually result in an overall emissions 

disbenefit; hence, EPA needs to ensure that the credits result in further reductions than 

those required by the emission standards, rather than in lieu of other reductions. 

The fo.rmula that EPGAA has suggested for idling credit is based on the light-duty credit 

calculation. A number of adjustments must be made to the formula to reflect the heavyduty fleet application. 

• Solar insolation rate: EPGAA suggested including an adjustment factor to account 

for the fact that the published benefits were assessed at one geographic location, 

Golden, Colorado, which does not reflect the average solar insolation rate in the 

country. This is fine, although ARB staff believes this adjustment would be 

insignificantly small compared to other needed adjustments. 

• Daytime idling percentage (lo): As EPGAA. mentions, the formula must be adjusted 

to compensate for the portion of idling time that occurs during daytime hours, 

preferably the hours when the solar radiation is substantial. Unfortunately, these 

data do not seem to be readily available. EPA offered some educated 

guess/anecdotal-based estimates as a starting point. Assuming that truckload 

carriers might drive .significant hours at night to avoid traffic congestion, EPA \ 

suggested a 50/50 split between daytime and nighttime idling. For the less-thantruckload and vocational freight, there is potentially more loading and unloading 

time, presumably during business hours, but likely less hoteling. EPA suggested a 

70/30 split for this category. For vocational vehicles, EPA has idling weighting 

factors by speed bin. EPA suggests an 80/20 split, with most idling occurring during 

daytime hours. ARB does not have these data in-house; however, ARB does have 

some limited data on Class 5-7 trucks previously discussed, which suggests that 

these vocational truck types idle about 50 percent of the time, presumably during 

"normal working hours". A Texas study (AACOG, 2011) suggested that trucks 

stopped at rest areas are most likely to be idling at night, which might be contrary to 

the presumption of night-time driving for the truckload carriers. 

• Thermal comfort adjustment: As previously discussed, thermal benefits would only 

accrue when the otherwise-idling engine is shut off. This could happen during 

periods when it is only being idled to provide cooling, the ambient conditions are 

moderate, and the idling period is short. Long idle times will still result in an 

8 
- 

------- -~~- -- ----------

excessively warm cab regardless of the efficacy of solar control glazing. This one 

adjustment would likely significantly reduce the size of any available credit. 

• Future impact from increased hoteling electrification and other technologies: Truck 

stop electrification is increasingly available. This technology allows the truck to hook 

into the power grid for thermal comfort and accessories. The engine is then shut 

down. Other methods to reduce engine idling for thermal comfort include batterypowered systems, and thermal energy storage systems. To the extent that these 

idling alternatives are utilized, the benefit of solar control paint and glazing to reduce 

idling use is minimized. Use of these approaches simultaneous with idle credits 

would result in inappropriate credit use. With the current nationwide trend in idling 

restrictions, the trend in idling time ought to be in a significant decline. Nonetheless, 

approaches such as solar control glazing and solar reflective paint will allow a 

battery-powered system to be downsized, thus somewhat reducing its weight and 

power needs. Other types of thermal energy storage systems could also be 

downsized, with similar benefits. The electricity draw at an electrified truck stop 

would also be slightly reduced, reducing grid energy demand and possibly, peak 

energy usage. 

Thus, while the proposed Z value of 0.5 suggested by EPGAA seems reasonable, 

additional adjustment factors are required. The lo term proposed by EPGAA appears to 

only address the portion of the time that idling occurs during the day, which ought to be 

specific to truck class. Since staff believes that the benefit would only accrue during the 

day during those periods of the year with moderate ambient conditions, and for stops of 

30 minutes or less, and utilizing the assumptions included in Section II.C, corrected as 

appropriate, a more detailed correction factor should be applied to 10 beyond the 

percent of idle time that occurs during the day. The correction factor should include the 

percent of the year when conditions are moderate (50 percent), the percent of the idling 

time that is for loading, unloading/meals (75 percent), corrected for the portion of these 

stops that are 30 minutes or less (50 percent), and the percent of the time that the 

vehicle is idling for thermal comfort, since idling for other purposes would presumably 

not be affected (65 percent), corrected for the portion of the thermal comfort idling that 

is for cooling (50 percent). This gives an overall correction factor of around 6 percent of 

the current engine operation time that could be reduced by thermal comfort's 

contribution to potential idle reduction. The calculation, shown below, would also need 

to be converted into the metric used for the Phase 2 GHG standards. 

'[,.X G· 

[ Credit= Z x 6 n 1 

G 1 l x 10 x L x 0.0611 

11 Z is a fraction representing the relationship between glazing performance and interior temperatures of a parked 

vehicle. T; is the thermal performance of the T' piece of glazing. G; is the area of that piece of glazing, while G is 

9 
It is also important that the credit include in some way a mechanism to ensure that 

replacement glazing maintains at least the same level of solar control as that assumed 

in the credit calculation for manufacturers utilizing the credit. If not, actual idle time 

reductions will last only as long as the original glazing. 

IV. Conclusions and Overall Recommendations 

In sum, ARB supports an idling reduction credit based on the use of solar control 

glazing but believes the approach must be refined beyond that proposed by EPGAA to 

incorporate better idling data. Further, the credit should be based on the reduced fuel 

consumption resulting from a reduction in idle time, not on potential benefits from air 

conditioner downsizing as was the LEV credit. ARB does not support an additional 

separate credit for solar control paint and glazing that would apply to the driving portion 

of the duty cycle. It is important to reiterate that while it might appear that the LEV 

credit is a driving credit, it was determined based on the ability of these controls to 

reduce the interior temperature of parked cars, thereby allowing manufacturers to 

downsize the air conditioner while still cooling the car in a suitable time period. 

Therefore, the LEV credits are actually parked car credits manipulated into a per/mile 

metric. 

ARB suggests the following formula, adjusted into the appropriate metric for the Phase 

2 GHG standards and adjusted for anyimprovements in staff assumptions, be used to 

determine credits for solar control glazing for heavy-duty trucks, in conjunction with a 

requirement that replacement glazing be of similar solar control levels as the glazing 

upon which the credit was calculated. 

\ 

Credit~[zxt,T,~G'] xl0 xL x0.06 

References: 

AACOG, Alamo Area Council of Governments. Heavy-Duty Vehicle Idle Activity and 

Emissions, San Antonio-New Braunfels MSA. 2011. 

ATRI, American Transportation Research Institute Compendium of Idling Regulations. 

Nov 2013. 

the total glazing area in the vehicle. 10 is the percent of time that idling occurs during the day, and Lis the solar 

insolation rate adjustment factor discussed previously. 

10 
Gaines, L., Vyas, A., Anderson, J., "Estimation of Fuel Use by Idling Commercial 

Trucks," 85th Annual Meeting of the Transportation Research Board, Washington, D.C., 

January 22-26, 2006, Paper No. 06-2567. 

Lustbader, J, C Kreutzer, MA Jeffers et al. Impact of paint color on rest period climate 

control loads in long-haul trucks. SAE Technical Paper 2014-01-0680. 

Lustbader, J, T Venson, S Adelman et al. Application of sleeper cab thermal 

management technologies to reduce idle climate control loads in long-haul trucks. SAE 

Technical Paper 2012-01-2052. 

Lutsey, N, C Brodrick, D Sperling, and C Oglesby. Heavy-Duty Truck Idling 

Characteristics: Results from a Nationwide Truck Survey. Transportation Research 

Record: Journal of the Transportation Research Board, No. 1880, TRB, National 

Research Council, Washington DC pp 29-38. 2004. 

Rugh, J, R Farrington. Vehicle Ancillary Load Reduction Project Close-Out Report. 

Technology Report NREL/TP-540-42454. January 2008 

US DOE. Energy Efficiency and Renewable Energy. Vehicle Systems Simulation and 

Testing. DOE/EE-1023. pp 254-260. 2013. 

Total solar transmittance test methodology: ISO 13877:2008 "Safety glazing materialsMethod for determination of solar transmittance" 

\ 

11