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Emissions and noise mitigation through use of electric ...

06 Aug.,2024

Emissions and noise mitigation through use of electric ...

Abstract

Gasoline-powered motorcycles contribute disproportionately to traffic noise and emissions, so motorcycle electrification merits investigation. Recent advances in battery efficiency allow electric motorcycles (EMCs) to join electric cars and bicycles as a viable consumer option. This study quantifies noise and emissions using both simulations and experimental data, examines the factors that make EMCs big offenders and uses popular EMC specifications to estimate the costs and benefits of electrification in the USA. Motorcycles produce more CO, CH4, NOx, HC and particulate matter than passenger vehicles per vehicle-mile travelled. Due to limited regulation of motorcycles and weak enforcement, the perceived noise of motorcycles exceeds that of most other vehicles, being roughly double that of automobiles at speeds of over 30 mph and surpassing even that of medium trucks and buses at speeds of over 50 mph, at which point motorcycles exceed the 80 dBA US standard limit. Electrification can resolve such issues, although range limitations and high prices are presently a barrier to widespread adoption. In order to realize these environmental benefits, it is important that electrification occur with a corresponding shift away from coal as an energy source. Stricter emission regulations and stronger enforcement of existing prohibitions on certain forms of customization could also reduce the outlier status of gasoline-powered motorcycles.

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1. Introduction

Motorcycles (MCs) often serve both recreational and transportation purposes. In crowded cities, where parking is scarce, their small size is an asset. In South and Southeast Asia, motorcycles regularly dominate city streets [40]. Their small size does not reduce their noise or emissions much, however. The two-stroke and four-stroke emissions of motorcycles harm human health, while their noise is both a nuisance and a health issue.

Fig. 1

Weighted noise emissions by vehicle type vs cruise speed [21]

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The burgeoning market of electric motorcycles (EMCs), fuelled by the changing landscape in technology, provides an opportunity to mitigate such impacts. For both traditional and electric motorcycle usage, safety remains a concern. The number of years a motorcyclist has been riding is inversely correlated with crash risk, as is helmet use [18]. Nonetheless, the US fatality rate of 54.58 deaths per 100&#;000 registered motorcycles was six times the rate for passenger cars. Assuming an average automobile occupancy of two people, motorcyclists die at 58 times the rate of passenger-car occupants per person-mile travelled [36]. As of , there are 8&#;600&#;936 registered motorcycles in the United States, having travelled a combined total of 19&#;606 million mi [36].

The scope of this paper is limited to motorcycle noise and emissions in the USA and the impacts from electrification. Motorcycle noise and emissions are increased by aggressive driving and regular revving, even when idling. New and recently repaired engines are thought to require a &#;breaking-in&#; period, and during this period the rider may rev the engine to vary engine speed [11]. There is also a widespread belief among riders that &#;loud pipes save lives&#; by drawing attention, although this belief is contradicted by studies that have found louder motorcycles are more likely to be involved in collisions [46]. Cultural factors and aesthetic preferences may also contribute to a rider&#;s preference for louder motorcycles [46].

The potential for electrification to reduce negative impacts has been explored by Simpson [43], Ehsani et al. [13], Tuttle [47] and others, but the bulk of research has been on passenger cars and trucks. Considerations of electric two-wheeled vehicles are dominated by e-bikes [8, 12, 51]. In contrast, this paper analyses experimental and simulation data to identify motorcycles&#; sound and emissions impacts and the potential for mitigation through electrification.

2. Noise emissions

A demand for high-speed transportation typically comes with increased noise pollution [34]. However, motorcycles are the exception to this rule. As seen in Fig. 1, their sound surpasses that of most other vehicles at speeds above 50 mph [21]. Since the engine of a motorcycle is not fully covered by the cowl, compared to the engines of automobiles hidden under hoods, the noise cannot be easily suppressed.

Fig. 2

Vehicle sound levels vs speed (data from FHWA-TNM )

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Table 1

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Factors affecting motorcycle dB: regression results

Variable

Coefficients

t-stat

P-value

Ambient noise level1..40.000Distance from sound meter (m)0..80.081Motorcycle recently started?&#;9.613&#;3.80.001Motorcycle accelerating?4..30.028Rider wearing helmet?&#;1.704&#;1.50.139Number of observations40Adjusted R-squared0.712Variable

Coefficients

t-stat

P-value

Table 1

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Factors affecting motorcycle dB: regression results

Variable

Coefficients

t-stat

P-value

Coefficients

t-stat

P-value

To further illustrate how motorcycle noise disproportionately contributes to overall traffic noise, the following data, as shown in Fig. 2, was collected from the Federal Highway Administration&#;s (FHWA) TrafficNoise Model 2.5 (TNM 2.5). The data is based on averages from a sample of of each type of vehicle.

2.1 Methodology

For the purposes of gathering simplified information to compare motorcycle noise emissions to those of other vehicle types, data from the TNM 2.5 Lookup Tables for hard ground was used. With this information, accurate comparisons across different vehicles can be formed. Receiver distance was expected to have a large impact on the LAeq output from the vehicles. LAeq (equivalent continuous sound pressure level) is the average sound pressure level produced over a given period of time. Both a short-range receiver distance and a long-range receiver distance were plotted.

2.2 TNM noise results

The data indicates motorcycles surpass selected vehicle types at higher speeds at both short and long ranges. Note that motorcycles approach 80 dBA, the US standard limit, at speeds of just 50 mph. Motorcycles have a much smaller carrying capacity, in terms of passengers and goods, yet account for more traffic noise than automobiles, medium and heavy trucks, and buses. Since LAeq is measured on a logarithmic, rather than a linear scale, small differences in dBA values can create substantial differences in perceived intensity. Since motorcycle engine size varies, one can assume that motorcycles with larger engines greatly exceed these predicted averages. This is problematic because noise exceeding 85 dBA is hazardous [7]. Prolonged exposure to such noise levels can be more damaging.

Perceived loudness from specific LAeq exposure varies widely from person to person. Due to this variability, quantifying specific perceived volume would not be useful for application. However, it is generally understood that a difference of 10 dB translates to a sound that is perceived as twice as loud [34], so motorcycles traveling at higher speeds may be perceived as nearly twice as loud as automobiles at the same speed.

3. Variables affecting noise: experimental data

To illuminate factors influencing gasoline-powered motorcycle sound levels, the data studied here, as shown in Table 1, was sampled from motorcycles operating in Austin, Texas. Data was collected on a busy, low-speed arterial with traffic signals. Samples were measured within a distance of 3&#;21 m.

3.1 Method

Roadside measurements of passing motorcycles (n&#;=&#;40) were made using a sound pressure level meter. Variables noted include meter distance from the source, speed (estimated by speed limit), observed acceleration, and a number of rider and motorcycle attributes. Explanatory variables were transformed into binary sets, and a value of 0.5 was assigned to unknown data points. Four OLS iterations were performed for the sample. Variables with large P-values were extracted from the data set, one at a time, following each iteration. The order in which these variables were discarded was as follows: Male? (P =&#;0.515), US Manufacturer? (P =&#;0.558) and Moped vs Motorcycle (P =&#;0.221).

3.2 Experimental noise data

Gender of the driver, vehicle manufacturer and vehicle type (scooter vs motorcycle) were found to be poor predictors of motorcycle sound level. As expected, sudden accelerations and distance from the device were strong predictors of maximum dB recorded. Ambient sound (P =&#;4.91E-7) was the most statistically significant for the sound level. Interestingly, motorcycles that were just starting were quieter than those operating on the road during sampling. Measurements categorized as a motorcycle having recently been started took place soon after this initial start-up, where the sampling was taken near a designated motorcycle, moped and scooter parking area. The motorcycles of riders without helmets were somewhat louder than those ridden by helmeted riders. Results suggest riding style and context may be more influential factors on noise emissions than the characteristics of the motorcycle.

Further research in a quieter environment, with a larger sample or weighting for model popularity, could expand these results. Similar experiments in other regions and countries could provide insight into the effectiveness of different models of regulation and enforcement.

4. Motorcycle sound laws

The US Environmental Protection Agency (EPA) has set a standard upper limit on motorcycle sound levels, at 80 dB measured at 50 ft, with constant engine speed at 50% RPM, but US states differ in specific additional limits, restrictions on tampering with acoustical equipment and enforcement [49]. A motorcycle may be perfectly legal in one state, yet in violation of the law if it crosses into another state.

US state-mandated sound limits range from no restrictions at all to limitations dependent on speed, engine size or year of manufacture [1]. Cut-off years vary among the states that have different limits for motorcycles of different ages. California has a tiered system, with incrementally lower maximum legal levels for motorcycles manufactured between and . Florida, in contrast, has different standards for those motorcycles built before and after [1].

Forty-six US states, including Texas, have muffler laws that require that the factory-installed muffler prevent &#;excessive or unusual noise&#; and forbid acoustical modifications such as muffler cutouts and bypasses (Texas State Law Sec. 547.604 [27]). Nonetheless, aftermarket pipes are easily obtained, and customizations are challenging for law enforcement to identify [19]. Oregon, New York and Montana specify maximum decibel levels at specific distances [1]; the equipment to obtain accurate readings can be costly, however, and is rarely available when enforcing regulations [19].

4.1 Japan, the European Union and Singapore

Regulations can also vary dramatically between and within other countries. Japan sets different sound limits based on engine size and depending on whether the motorcycle is cruising, accelerating or stationary, with those limits ranging from 65 dBA to 94 dBA [28]. Permissible sound levels in the European Union (EU) also vary by motorcycle type, from 74 dBA to 80 dBA [17]. The EU also carefully details procedures for measuring sound levels [17]. Singapore sets the maximum decibel level at 94 dBA, and references both European and Japanese standards for noise emissions [16].

Fig. 3

Average US emission rate changes for motorcycles over time (output from MOVES)

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5. Tailpipe emissions

Emissions from conventional motorcycles have detrimental environmental and health effects. As technology has improved, motorcycles have not seen the same progress in reducing emissions as other vehicles. Motorcycles emit less CO2, NOx, SO2 and PM10 per person-mile travelled than most cars, but more VOC and CO if there is no catalytic converter present [19]. Motorcycles with smaller engines have better mileage and produce fewer emissions, but motorcycles with larger engines perform worse than most other vehicles of all types [19].

Motorcyclists have been found to be at a greater risk of respiratory illness and decreased mucociliary clearance (MCC) [2]. This can be linked to a rider&#;s exposure to the emissions from both their vehicle and surrounding vehicles. In Brant&#;s study, commercial motorcyclists were found to be exposed to a median level of 75 mg/m3 of NO2 during the 14-day monitoring period. 92% of the subjects reported airway symptoms, and 32% reported slower nasal MCC. For contrast, 19% of healthy individuals have slowed MCC [2].

In , the US EPA updated federal regulations on motorcycle emissions, which had remained largely unchanged since their introduction in the late s [42]. Under the new regulations, motorcycles are still allowed higher emissions than light-duty vehicles (LDVs). MC engines tested at 18&#;600 mi are permitted to emit up to 1.29 gm/mi of HC and NOx, while most LDVs are limited to no more than 0.018 gm/mi of HCHO and 0.2 gm/mi of NOx. MCs are allowed up to 19.3 gm/mi of CO, while LDVs are allowed 4.2 gm/mi. The EPA does not set any requirements for particulate matter (PM) emissions on MCs. Internationally, standards vary; European emission standards are generally stricter than US EPA standards [20].

Enforcement of emission standards, or lack thereof, also presents an issue. In Texas, a handful of cities require emissions testing on some vehicles, but motorcycles are completely exempt [45]. Even agencies with a reputation for strict enforcement, like the California Air Resources Board, provide exemptions for motorcycles [5].

5.1 US emissions over time, &#;

To see how motorcycle emissions have changed over time, and how those changes compare with emissions from passenger vehicles (PVs), US emissions data was evaluated using US EPA software, MOVESa. This Motor Vehicle Emission Simulator (MOVES) generates emissions and energy consumption for different vehicle types using emissions data gathered between the s and the s.

The following data was created through a MOVES simulation for gasoline-powered motorcycles in , , , and . The simulation estimated the combined starting and running emissions from motorcycles for the entire USA. The total distance travelled was also estimated, enabling the calculation of the total average US emissions per mile for the presented species. The percentage of the initial rate for each species is shown in Fig. 3.

Fig. 4

Average US emission rate changes for passenger vehicles over time (output from MOVES)

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Table 2

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Average US emission rates for MCs and PVs in (output from MOVES)

Vehicle

CO2 (g/mi)

CO (g/mi)

CH4 (g/mi)

N2O (g/mi)

NOx (g/mi)

PM 10 (g/mi)

PM 2.5 (g/mi)

Sulphate PM 2.5 (g/mi)

HC (g/mi)

Motorcycle365..000.......236Passenger car392.786.......85E-40.561Vehicle

CO2 (g/mi)

CO (g/mi)

CH4 (g/mi)

N2O (g/mi)

NOx (g/mi)

PM 10 (g/mi)

PM 2.5 (g/mi)

Sulphate PM 2.5 (g/mi)

HC (g/mi)

Motorcycle365..000.......236Passenger car392.786.......85E-40.561

Table 2

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Average US emission rates for MCs and PVs in (output from MOVES)

Vehicle

CO2 (g/mi)

CO (g/mi)

CH4 (g/mi)

N2O (g/mi)

NOx (g/mi)

PM 10 (g/mi)

PM 2.5 (g/mi)

Sulphate PM 2.5 (g/mi)

HC (g/mi)

Motorcycle365..000.......236Passenger car392.786.......85E-40.561Vehicle

CO2 (g/mi)

CO (g/mi)

CH4 (g/mi)

N2O (g/mi)

NOx (g/mi)

PM 10 (g/mi)

PM 2.5 (g/mi)

Sulphate PM 2.5 (g/mi)

HC (g/mi)

Motorcycle365..000.......236Passenger car392.786.......85E-40.561

As emission control and catalytic technologies advance, one expects harmful emissions of all types to decrease. Since some emission species have not decreased, the existing emissions policy or enforcement of motorcycle laws may be inadequate. CO2, N2O and NOx increase over time, while the other four species decrease. The improvements in emission species might be due to better fuel economy, engine design or enforcements. Nonetheless, the three species that show increase in rate over time suggest more improvement in motorcycle design and stricter enforcements should be implemented. The sharp increase in nitrogen oxides is of particular concern; N2O increases tropospheric ozone and contributes to smog and acid rain [4, 39].

For comparison, the same emission species for duplicate years were calculated for all PVs across the United States. An identical procedure was used for Fig. 4 to make parallels clear. A comparison of the estimated total average emission rates is represented numerically in Table 2. MCs emit more CO, NOx and sulphate PM 2.5 per mile than PVs, which is assumed to be the result of incomplete combustion in MC engines compared to those of PVs. The results indicate most of the emission rates for motorcycles are higher than those for passenger cars, unlike the results predicted by Fagnant et al. [19]. The discrepancy may be caused by the differences in assumptions, simulation and experiment conditions, and methodologies used in each analysis. However, the changes in emission rates over time shown in Figs 3 and 4 can be used to compare emissions from motorcycles and passenger cars.

Table 3

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Details of five popular gasoline motorcycles

Year

Make

Model

Engine size (cc)

Fuel capacity (gal)

Fuel economy (mi/gal)

Range (mi)

Weight (lbs)

MSRP price ($)

SuzukiVanVan .HondaRebel .YamahaSCR.TriumphStreet Cup. (dry)10&#;Harley-DavidsonRoad Glide.&#;300Year

Make

Model

Engine size (cc)

Fuel capacity (gal)

Fuel economy (mi/gal)

Range (mi)

Weight (lbs)

MSRP price ($)

SuzukiVanVan .HondaRebel .YamahaSCR.TriumphStreet Cup. (dry)10&#;Harley-DavidsonRoad Glide.&#;300

Table 3

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Details of five popular gasoline motorcycles

Year

Make

Model

Engine size (cc)

Fuel capacity (gal)

Fuel economy (mi/gal)

Range (mi)

Weight (lbs)

MSRP price ($)

SuzukiVanVan .HondaRebel .YamahaSCR.TriumphStreet Cup. (dry)10&#;Harley-DavidsonRoad Glide.&#;300Year

Make

Model

Engine size (cc)

Fuel capacity (gal)

Fuel economy (mi/gal)

Range (mi)

Weight (lbs)

MSRP price ($)

SuzukiVanVan .HondaRebel .YamahaSCR.TriumphStreet Cup. (dry)10&#;Harley-DavidsonRoad Glide.&#;300

While motorcycle emission species are inconsistent in their changes over time, passenger vehicle emissions have significantly decreased in all areas, suggesting a technological or regulatory gap. In fact, passenger vehicles outperform motorcycles in emissions of most species, including nitrogen oxides and carbon monoxide, as of . According to MOVES prediction estimates, passenger vehicles will outperform motorcycles in nearly all emission species in the coming decades. This will exacerbate the gulf in emission costs per person-mile between PVs and MCs. Electrification is one route to mitigation. Regulations could also play a role.

6. Electric motorcycles

Many traditional MC manufacturers plan to release electric models in the coming years [24, 35, 52]. EMCs are drastically more energy efficient than conventional motorcycles. For instance, the Zero S Motorcycle has a manufacturer-estimated equivalent fuel economy of 475 mi/gal in the city and 240 mi/gal on highways, using the US EPA&#;s formulas [54]. These fuel economies are over 10 times the average 21.5 mi/gal of light-duty vehicles in the USA [44] and over four times the 53 mi/gal average of a US sample of 229 motorcycles [19].

EMC manufacturers also note the need for no routine drivetrain maintenance [54], but consumers may be concerned about EMC batteries taking too long to charge and being too expensive or too heavy [30]. Cherry et al.&#;s [9] stated-choice study in Vietnam found that consumers responded to economic incentives, with sales tax having a greater effect on vehicle choice than purchase price. The same study found improvements in range, speed and acceleration made EMCs more appealing. Guerra&#;s research in Solo, Indonesia [26] found strong market potential for EMCs, especially as battery technologies improve and climate change concerns lead to increased demand for alternatives to petroleum.

The results of a study of mode-choice transitions in Kunming, China, where motorcycles are severely restricted due to safety and congestion concerns, implied that former car users were less likely to switch back to cars over time, possibly because e-bikes provided an appealing alternative [8]. In cities without such restrictions, EMCs may provide a similar role, although the researchers warned against applying their findings too generally [8]. Motorcycle use varies widely between countries. For instance, in contrast to the relatively low motorcycle mode share in the USA, 85% of Indonesian households and 87% of households in Thailand have at least one working motorcycle or scooter, with comparable percentages in other Southeast Asian countries [40].

A study in Thailand showed that further improvements to the electricity mix consumed and the recycling of batteries used in electric vehicles (EVs) could better allow for sustainable implementation of electric bikes and motorcycles. Lead-acid batteries were found to be less expensive than lithium-ion batteries, but to require more frequent replacement [29]. To reduce metal depletion and toxicity, batteries must be recycled [29]. The recycling of lead-acid batteries can prevent 98% of impacts from toxicity. EMCs can be a sustainable transport option so long as cleaner electricity grid energy production and battery recycling are implemented [29].

7. Benefit-cost analysis

To evaluate the potential costs and benefits of electrification, a sampling of EMCs available today was compared with five popular gasoline-powered motorcycles on features and capabilities.

The following tables contain relevant manufacturer-estimated features of popular gasoline motorcycles and selected EMCs. As EMCs are relatively new, popularity rankings are not available as of this writing, so EMC models were selected from major manufacturers that provided the necessary information for comparison.

Table 4

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Specifications for five electric motorcycles available in the USA

Year

Make

Model

Max. battery capacity (kWh)

Highway range (mi)

Charging timea (hr)

Top speed (mph)

Weight (lbs)

MSRP ($)

ZeroS ZF6.56..7
(standarda)&#;AltaRedshift SM5. (Level 2), 6 (Level 1)&#;ZeroSR ZF13.013..9 (standarda)&#;EnergicaEgo11..5 (level 2), 0.5 (DC fast charge)&#;LightningLS-, 15, (level 2), 0.5 (DC fast charge)&#;900Year

Make

Model

Max. battery capacity (kWh)

Highway range (mi)

Charging timea (hr)

Top speed (mph)

Weight (lbs)

MSRP ($)

Table 4

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Specifications for five electric motorcycles available in the USA

Year

Make

Model

Max. battery capacity (kWh)

Highway range (mi)

Charging timea (hr)

Top speed (mph)

Weight (lbs)

MSRP ($)

Make

Model

Max. battery capacity (kWh)

Highway range (mi)

Charging timea (hr)

Top speed (mph)

Weight (lbs)

MSRP ($)

Electrification would not compromise performance. The Lightning LS-218, for example, won a race in record speed, beating competing production motorcycles [31]. Most of the popular EMCs available are intended for sports and performance purposes, which helps account for their higher MSRP. Of the sampled vehicle makes and models, the EMCs had a 55.7% higher average MSRP, although Zero offers more affordable EMCs for common use. Although weight difference is a common complaint associated with electrification, weights were comparable between electric and gasoline motorcycles.

Range and charging time are important factors when considering electrification. While most EVs can be charged through standard home charging, level 2 and level 3 chargers significantly reduce charging time. Many manufacturers do not list a standard charging time, presumably because the information might discourage purchases. Most manufacturers offer additional accessories that significantly decrease charging time. This makes charging times difficult to quantify, as they can vary even between motorcycles of the same make and model, depending on consumer choices.

Although EMCs cost less to charge than gasoline motorcycles cost to fuel, battery capacity limits the travel range. EMCs had a shorter range per full charge than gasoline motorcycles on a full tank in all the cases listed. The EMCs sampled averaged a 61.2% shorter range at highway speeds. As estimated city ranges are greater than highway estimates, range limitations would be less of an issue in dense, urban environments, where trip distances are typically shorter.

7.1 External environmental costs

While transportation made up only 0.2% of the demand on the US electricity grid in [14], that number will likely grow as EVs become more popular. For electric motorcycles, emissions are present not at the tailpipe, but at the power plants that provide the battery&#;s charge. As such, outputs are highly dependent on the method used to produce electricity.

Emission costs can also vary depending on where pollutants are emitted; output at tailpipe-level in a city has more ramifications for human health, for instance, than output from a remote power plant, so &#;exporting&#; emissions through electrification could have benefits even when emission rates are similar to those of gasoline-powered vehicles [41]. Motorcycle fuel consumption is approximately 30% greater in cities than in the countryside, so emissions from combustion may be even more concentrated in urban areas, and thus more damaging, than this data suggests [6].

Urban/suburban and rural areas were defined based on the US Census Bureau, which provides urban population figures for each state [48]. The most urbanized state is Washington, DC, with an urbanization level of 100%, while the least urbanized is Maine with 38.7%. In this analysis, those states with a higher urbanization percentage than the US average (74.1%) were defined as urban/suburban areas, while the remainder were defined as rural areas.

The average energy consumption of the five EMC models featured in Table 4 was calculated to be 0. kWh/mi. Using output rates for the United States electricity grid, as reported in the Emissions & Generation Resource Integration Database (eGRID), the per-mile emissions of five species that EMCs indirectly produce were estimated and contrasted with the MOVES output of gasoline-powered motorcycles&#; emissions (Table 5). During this calculation, different values were derived for urban/suburban and rural areas. This data does not fully capture the impacts of extreme outliers; a California Air Resources Board survey [3] found that nearly 38% of motorcycle owners admitted to replacing exhaust systems and, as noted above, many of those replacements were likely made to increase power or change the motorcycle&#;s sound.

Table 5

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US grid emissions and annual motorcycle emissions

Rural areas

Emission speciesElectricity grid
output rate (g/kWh)bElectric motorcyclesGasoline-powered motorcyclesOutput rate (g/mi)Total annual outputc (g/year)Costs per mile ($/mi)Yearly costa ($/year)Output rated (g/mi)Total annual outputc (g/year)Costs per mile ($/mi)Yearly costa ($/year)CO..&#;...&#;..68CH40...250..720...25N2O0...520..050..40..51NOx0...050..411...44SO20...640..530.e28.10..27Total costs0..88Total costs0..15Urban/suburban areasEmission speciesElectricity grid output rate (g/kWh)bElectric motorcyclesGasoline-powered motorcyclesOutput rate (g/mi)Total annual outputc (g/year)Costs per mile ($/mi)Yearly costa ($/year)Output rated (g/mi)Total annual outputc (g/year)Costs per mile ($/mi)Yearly costa ($/year)CO..&#;...&#;..10CH40...100..160...22N2O0...390..120...45NOx0...460..151...32SO20...450..090...12Total costs0..65Total costs0..20Rural areas

Table 5

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US grid emissions and annual motorcycle emissions

Rural areas

The vehicle-miles-travelled (VMT) differs between urban/suburban and rural areas. Rural areas have lower population density; thus, the VMT in these areas tends to be higher than in urban areas. The National Household Travel Survey [23] suggests that the VMT in urban/suburban areas is 93% of the US average for journeys made with passenger cars, with a corresponding figure of 106% for rural areas. This research assumes that the same ratio can be applied to motorcycles: mi/year for rural areas and mi/year for urban/suburban areas, while the US average was found to be mi/year, based on the average mileage of registered US motorcycles from to [22].

The average per-mile output estimates for EMCs are less than those for most passenger cars and conventional motorcycles for CO2, NOx and other species not featured due to negligible output. However, in our results, EMCs produced more emissions with greater environmental costs, such as sulphur oxides and methane. This is likely because some electricity sub-grids in the USA rely heavily on coal [37]. A direct comparison here between EMC and gasoline-powered motorcycle outputs could be misleading, however; as noted above, emissions due to EMCs occur at power plants generally situated to reduce the impacts of their output. Areas with greater use of renewables than the US average would also yield better emission rates for EMCs. For the optimal benefits of electrification to manifest, the transition must be accompanied by changes in the ways in which energy is produced and distributed.

Rural areas have higher costs for both gasoline-powered motorcycles and EMCs than urban/suburban areas. This may be due to the higher VMT and higher emission output rate in rural areas. Power plants in rural areas tend to emit more emission species than those in urban/suburban areas, suggesting that rural areas may rely less on clean and renewable energy. Table 5 therefore suggests that tailpipe emission levels in rural areas may be reduced to the levels of urban/suburban areas with electrification.

In Table 5, general emission valuations for the five species examined are presented in US dollars per metric tonne, and are the values recommended by the US Department of Transportation for CO2, NOx and SO2 emissions [50]. Values for CH4 and N2O are from Marten and Newbold [33]. Costs assume a 3% discount rate, and have been converted to dollars using the US Consumer Price Index (CPI). To approximate the lowered costs of emissions at power plants versus those of tailpipe emissions, the cost estimates for EMCs halve these values. These estimates assume a motorcycle in average condition; motorcycles modified to have more power and louder sound may emit more emissions, and therefore incur higher costs than the estimates in Table 5.

7.2 Noise costs

Quantifying the costs of traffic noise is challenging. Studies that base costs on highway noise, as is common in the USA, neglect the greater impact noise has on city streets [32]. Metrics that focus on impacts on residential values do not account for more general effects on quality of life, businesses, pedestrians or wildlife [25, 32].

This analysis uses an unweighted average cost of $0.13 per VMT for gasoline-powered motorcycles, as estimated in Litman&#;s review [32] and adjusted using the CPI to dollars. With an average yearly VMT of approximately mi for motorcycles (FHWA ) [22], this means the noise costs of gasoline-powered motorcycles will be $312 per vehicle on average. The noise from electric motors is so low that pedestrians have difficulty recognizing their presence by sound [53], to the extent that the possibility of adding sounds to warn pedestrians of approaching EMCs has been studied [38]. Assuming the noise produced by EMCs to be negligible, electrification could save an average of $312 per vehicle in annual noise costs.

7.3 Total per-mile external costs

The combined costs of the noise and emissions of conventional motorcycles were estimated at approximately $0./mi, versus $0./mi for electric motorcycles. Emissions appear to comprise most of the costs of motorcycle use, but this neglects extreme offenders. Future work could quantify the disproportionate impact of those motorcycles that have been modified to bypass manufacturing standards restricting noise or emissions.

8 Conclusions

While regulations and technological advancements have steadily reduced noise and emissions for passenger vehicles, motorcycles have not followed suit. US motorcycle emissions have experienced between a 60% decrease and a 10% increase, depending on gas species, over the five decades simulated in this study. For comparison, passenger cars are predicted to experience a 50&#;98.5% decrease, without accounting for higher passenger car occupancy.

Motorcycle sound can be perceived as nearly twice that of automobiles at high speeds. The psychological and health effects of increased urban noise can significantly impact dense urban populations. Motorcycles, despite having lower seating capacity than other vehicles, are one of the loudest contributors to traffic noise.

Motorcycles emit more CO, NOx and sulphate PM 2.5/mi than passenger cars, which is assumed to be the result of incomplete combustion in motorcycle engines. Moreover, nitrogen oxides and PM 2.5 produce smells; nearby pedestrians may therefore be offended by emissions from motorcycles more than those from passenger cars.

With little to no improvement in motorcycle gaseous emissions over the past few decades, and noise levels exceeding those of most other vehicle types, change is warranted. The electrification of motorcycles has the potential to reduce most emission species, with some caveats. Electric motorcycles, and electric vehicles in general, can help combat traffic noise. Per-VMT costs in noise and the five emission species studied total approximately $0. for gasoline-powered motorcycles and $0. for EMCs in rural areas, and $0. for gasoline-powered motorcycles and $0. for EMCs in urban/suburban areas.

Electrification does carry distinct barriers to implementation. Unless EMCs are paired with a shift to less polluting sources of energy, EMC adoption could increase social costs. Recycling of the lithium-ion batteries is also important to protect from battery-associated toxicity exposure. The price of EMC models would need to decrease for widespread and popular implementation. Moreover, the engines of conventional motorcycles will degrade, while power plants will become cleaner over time. Therefore, the benefits from electrification may be greater than has been identified in this paper. However, the estimates presented in this paper are based on an motorcycles in average condition. If more motorcycles are modified to have more power and louder sound than the assumptions made in this paper, the emissions and costs associated with motorcycles may be higher.

Further research could provide more insight into ways in which the negative impacts of gasoline-powered motorcycles might be reduced. Field testing of motorcycles in particular geographic locations could reveal problems faced in specific communities; for example, acoustical and exhaust modification may be more common in certain areas. Regional differences in energy sources, and how they may affect EMCs&#; environmental costs, could also be explored. Additional legislation to establish stricter manufacturing standards and to reliably enforce current design and tampering laws is also important. Priorities should be targeting emissions from all motorcycles and reducing the impacts of motorcycles modified to be far louder or more polluting than the average.

Author contribution statement

The authors confirm that their contributions to this paper were as follows: Michael Hernandez and Kara Kockelman conceived and designed the study; Michael Hernandez, James Lentz and Kara Kockelman analysed the data and interpreted the results; and Michael Hernandez, Kara Kockelman and James Lentz prepared the draft manuscript. All authors reviewed the results and approved the final version of the manuscript.

Conflict of interest statement. None declared.

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Electric motorbikes on course to take charge of EV space

The breakthrough in performance could propel e-motorcycle penetration to over 30% of the overall motorcycle market by , up from less than 1% today, Bain India said in a recent report.

Several startups including Matter Electric Motorcycles, Orxa Energies,

&#;We are at the cusp of an exciting era of electrification in the motorcycle segment that presents breakout investment opportunities in the Indian market,&#; said Vasudha Madhavan, founder and CEO of Ostara Advisors, an EV-focused investment bank. &#;We expect to see an EV startup unicorn emerge in the electric motorcycle space in the next 3-5 years,&#; she added.

Till now,

That is likely to change with several high performance, zero-emission e-motorcycles set to hit the Indian roads at prices comparable to those run on petrol.

In the next 12-18 months, electric motorcycles will become mainstream, said Mohal Lalbhai, founder and CEO of Matter Electric Motorcycles. &#;While there is a huge pent-up demand, the choices were limited,&#; he said.

Advanced Technology in Play

Now the electric motorcycle majors are able to achieve price and range parity with the ICE counterparts, thanks to falling battery prices.

If a 300-cc ICE (internal combustion engine) motorcycle retails at Rs 3.5-4 lakh, its equivalent electric counterpart will be priced around Rs 3.8 lakh, e-motorcycle makers said. In the case of range, the electric bike on a single charge can run 307 km while its ICE counterpart can run 250 km on a full tank of petrol, they said.

Within the ICE motorcycle segment, the mid and premium segment is growing faster than entry level bikes, and the same trend is expected for e-motorcycles.

&#;So, we see a consumer preference for higher end electric motorcycles, an equivalent to 400-500 cc ICE bikes,&#; said Narayan Subramaniam, cofounder and chief executive of Ultraviolette Automotive, which currently retails one model at around Rs 3.8 lakh, only out of Bangalore. The company plans to increase dealerships to 15 cities this year.

Electric motorcycles are getting increasingly advanced in terms of instant torque, ride-by-wire technology, and over-the-air software updates, which will see an increasing uptick in sales, industry executives said.

&#;Consumers are not going to move to electric unless you give a product equal in performance to their ICE counterpart,&#; said Ranjita Ravi, cofounder of Orxa Energies. &#;This is now possible as we are able to pack enough power at 80% less cost, thanks to the falling lithium prices.&#;

Orxa retails an electric motorcycle with a 20.5 kw power at Rs 3.5 lakh.

Kapil Shelke, founder of Tork Motorcycles, which makes its own battery packs and chargers, said, &#;Now, we are able to pack all the features into the electric motorcycle at a competitive price. Electric motorcycles will become the larger subset of the two-wheeler market, which is waiting to be captured.&#;

Accelerating growth in the premium two-wheeler segment has seen Indian two-wheeler majors partner with global players.

They are forming partnerships for e-motorcycles as well.

US e-motorcycle maker Zero Motorcycles is partnering with Hero MotoCorp to enter India. The partnership combines Zero&#;s expertise in power trains and electric motorcycles with Hero&#;s manufacturing and marketing capabilities.

TVS Motors has invested in Ultraviolette Automotive.

Royal Enfield is working on two electric motorcycle platforms: one in-house and one in collaboration with Spanish startup Stark Motorcycle, and the final product is expected to be ready this fiscal.

Meanwhile, India&#;s FAME II Scheme allows for a demand incentive of 15% of the ex-factory vehicle price or Rs 10,000 per kWh of battery pack, whichever is lower. For electric two-wheelers, vehicles with maximum ex-factory price of Rs 1.5 lakh can avail of the subsidy.

This means that an electric motorcycle designed for performance and range will be outside the subsidy net, experts said.

(You can now subscribe to our

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Mumbai: Motorcycles are set to power electric vehicle adoption in India in the coming months as traditional manufacturers vie with startups to roll out battery powered versions that match their petrol-driven counterparts in performance and range.The breakthrough in performance could propel e-motorcycle penetration to over 30% of the overall motorcycle market by , up from less than 1% today, Bain India said in a recent report.Several startups including Revolt Motors Oben Electric , Ultraviolette, Komaki, Tork Motors, and Kabira Mobility, and some of the traditional motorcycle majors including Royal Enfield are firming up new electric motorcycle launches over the next few months.&#;We are at the cusp of an exciting era of electrification in the motorcycle segment that presents breakout investment opportunities in the Indian market,&#; said Vasudha Madhavan, founder and CEO of Ostara Advisors, an EV-focused investment bank. &#;We expect to see an EV startup unicorn emerge in the electric motorcycle space in the next 3-5 years,&#; she added.Till now, e-scooters were riding the EV wave in the two-wheeler space.That is likely to change with several high performance, zero-emission e-motorcycles set to hit the Indian roads at prices comparable to those run on petrol.In the next 12-18 months, electric motorcycles will become mainstream, said Mohal Lalbhai, founder and CEO of Matter Electric Motorcycles. &#;While there is a huge pent-up demand, the choices were limited,&#; he said.Now the electric motorcycle majors are able to achieve price and range parity with the ICE counterparts, thanks to falling battery prices.If a 300-cc ICE (internal combustion engine) motorcycle retails at Rs 3.5-4 lakh, its equivalent electric counterpart will be priced around Rs 3.8 lakh, e-motorcycle makers said. In the case of range, the electric bike on a single charge can run 307 km while its ICE counterpart can run 250 km on a full tank of petrol, they said.Within the ICE motorcycle segment, the mid and premium segment is growing faster than entry level bikes, and the same trend is expected for e-motorcycles.&#;So, we see a consumer preference for higher end electric motorcycles, an equivalent to 400-500 cc ICE bikes,&#; said Narayan Subramaniam, cofounder and chief executive of Ultraviolette Automotive, which currently retails one model at around Rs 3.8 lakh, only out of Bangalore. The company plans to increase dealerships to 15 cities this year.Electric motorcycles are getting increasingly advanced in terms of instant torque, ride-by-wire technology, and over-the-air software updates, which will see an increasing uptick in sales, industry executives said.&#;Consumers are not going to move to electric unless you give a product equal in performance to their ICE counterpart,&#; said Ranjita Ravi, cofounder of Orxa Energies. &#;This is now possible as we are able to pack enough power at 80% less cost, thanks to the falling lithium prices.&#;Orxa retails an electric motorcycle with a 20.5 kw power at Rs 3.5 lakh.Kapil Shelke, founder of Tork Motorcycles, which makes its own battery packs and chargers, said, &#;Now, we are able to pack all the features into the electric motorcycle at a competitive price. Electric motorcycles will become the larger subset of the two-wheeler market, which is waiting to be captured.&#;Accelerating growth in the premium two-wheeler segment has seen Indian two-wheeler majors partner with global players.They are forming partnerships for e-motorcycles as well.US e-motorcycle maker Zero Motorcycles is partnering with Hero MotoCorp to enter India. The partnership combines Zero&#;s expertise in power trains and electric motorcycles with Hero&#;s manufacturing and marketing capabilities.TVS Motors has invested in Ultraviolette Automotive.Royal Enfield is working on two electric motorcycle platforms: one in-house and one in collaboration with Spanish startup Stark Motorcycle, and the final product is expected to be ready this fiscal.Meanwhile, India&#;s FAME II Scheme allows for a demand incentive of 15% of the ex-factory vehicle price or Rs 10,000 per kWh of battery pack, whichever is lower. For electric two-wheelers, vehicles with maximum ex-factory price of Rs 1.5 lakh can avail of the subsidy.This means that an electric motorcycle designed for performance and range will be outside the subsidy net, experts said.

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