What Are Flex Fuel Vehicles?

Flex Fuel Vehicles (FFVs) are internal combustion engine vehicles designed to operate on a wide range of gasoline-ethanol blends, from pure gasoline up to E85, which contains 85% ethanol and 15% gasoline. The underlying technology is not new; FFVs have been produced for decades, with major manufacturers like Ford, General Motors, and Chrysler offering models since the 1990s. The key difference from standard gasoline vehicles lies in the fuel system’s materials and calibration. Ethanol is more corrosive than gasoline, so FFVs use ethanol-resistant seals, gaskets, and fuel lines. Their engine control units (ECUs) have sensors that detect the exact ethanol content in the fuel tank and adjust ignition timing, fuel injection, and air-fuel ratio accordingly. This allows the vehicle to run efficiently on any blend between pure gasoline and E85.

Ethanol itself is an alcohol-based fuel produced primarily from corn in the United States, though cellulosic ethanol from agricultural residues, wood chips, and dedicated energy crops is emerging. The U.S. Department of Energy’s Alternative Fuels Data Center reports that ethanol can reduce lifecycle greenhouse gas emissions by roughly 34% to 44% compared to gasoline, depending on the feedstock and production process. E85, the most common high-ethanol blend, has a lower energy density than gasoline (about 73,000 BTU per gallon vs. 114,000 BTU), which means fuel economy on E85 is typically 15% to 27% lower than on gasoline. However, the price of E85 is often lower per gallon, which can offset the reduced range. For fleet operators considering cost and environmental goals, understanding this trade-off is essential.

The U.S. Energy Information Administration notes that there are roughly 20 million FFVs on American roads today, but many owners are unaware their vehicle is flex-fuel capable because the technology is invisible during normal operation. A simple check of the fuel door or owner’s manual can identify an FFV—often indicated by a yellow ring around the fuel filler nozzle. This underutilization represents a missed opportunity for cleaner fuel adoption.

Nashville’s Smart City Goals

Nashville’s smart city framework, formally known as Smart Nashville, is a comprehensive plan to harness technology and data to improve urban life while reducing environmental impact. The initiative, launched in 2016 and updated in 2020, spans transportation, energy, public safety, and digital equity. The transportation pillar specifically targets a 30% reduction in per capita greenhouse gas emissions by 2030, relative to 2014 levels, and a transition to a zero-emission public transit fleet by 2041. To achieve these targets, the city is investing in electric vehicle (EV) charging infrastructure, intelligent traffic management systems, and alternative fuel adoption across municipal operations.

Unlike some cities that focus solely on electrification, Nashville recognizes the value of a multi-fuel approach. The city’s climate action plan highlights that while EVs will dominate long-term, FFVs offer an immediate, cost-effective way to reduce emissions from the existing vehicle stock—especially for heavy-duty fleet vehicles where EV technology is still maturing. Nashville’s geographic location in a major corn-producing region (Tennessee ranks high in corn and soybean production) also makes ethanol a locally relevant resource, supporting agricultural economies and reducing transportation fuel costs.

A key component of Smart Nashville is the Nashville Fleet Sustainability Policy, adopted in 2019, which requires all new light-duty municipal fleet purchases to be alternative fuel vehicles (FFV, EV, or plug-in hybrid) when commercially available. The policy has already shifted a significant portion of the city’s 2,800-vehicle fleet. According to the Nashville Fleet Management Division, as of early 2024, nearly 60% of light-duty vehicles are FFVs, and the city operates over 200 electric vehicles as well. The remaining gasoline-only vehicles are gradually being phased out.

Integration of FFVs into Nashville’s Transit

Public transit in Nashville is managed by the Nashville Metropolitan Transit Authority (MTA) and the Regional Transportation Authority of Middle Tennessee (RTA). The city’s bus fleet has traditionally run on diesel, but MTA is actively piloting alternative fuels. While electric buses are part of the long-term plan (the first battery-electric buses entered service in 2022), the MTA has also introduced E85-powered paratransit vans and support vehicles. These FFVs operate on the same routes as standard gasoline vehicles, but with the added benefit of lower tailpipe CO2 emissions. The paratransit vehicles are especially suited to FFV technology because they tend to have shorter daily mileage and can refuel within the existing infrastructure near the downtown depot.

Outside of public transit, Nashville’s city-owned utility vehicles—used for parks maintenance, water management, and traffic signal repairs—are increasingly running on E85. The city reports that each FFV replaces roughly 3,600 gallons of gasoline per year with E85, cutting annual CO2 emissions by an estimated 8,000 pounds per vehicle. For the fleet of approximately 1,500 FFVs currently in municipal service, that translates to a reduction of over 12 million pounds of CO2 annually—equivalent to removing 1,200 passenger vehicles from the road.

Supporting Infrastructure

Infrastructure is the linchpin of any alternative fuel adoption. Nashville has taken a deliberate approach to expanding E85 availability. As of early 2025, there are 14 public E85 fueling stations in the Nashville metropolitan area, up from just five in 2018. The city has partnered with local fuel distributors and the Tennessee Department of Environment and Conservation to install pumps at key locations, including the Nashville Fleet Services Center (which serves municipal vehicles) and high-traffic corridors like Murfreesboro Pike and West End Avenue. The city also uses a grant from the U.S. Department of Energy’s Clean Cities program to offset the cost of station conversions—retrofitting a gasoline pump to dispense E85 costs roughly $20,000 to $40,000, a fraction of the cost of building a new EV charging hub.

The city’s smart city platform Nashville Intelligent Transportation System (ITS) integrates fueling station data into real-time traffic and fuel availability maps, accessible through a mobile app called Nashville Go. Residents can locate the nearest E85 station, check fuel prices, and see estimated wait times—mirroring the convenience of EV charging apps. This data-driven approach encourages adoption by reducing one of the biggest barriers: "range anxiety" for alternative fuels.

Challenges remain. Ethanol’s lower energy density means that fleets need more frequent refueling, and the current E85 station density is still low compared to gasoline stations (over 200 in the metro area). The city is addressing this through a targeted expansion plan: by 2028, Nashville aims to have at least 30 public E85 stations, with strategic placement along major freight and commuter corridors. Private stations are also being incentivized through a streamlined permitting process and a small tax rebate for owners who install E85 dispensers.

Benefits of Combining FFVs and Smart City Tech

Integrating FFVs into Nashville’s smart city framework creates synergies that go beyond tailpipe emissions reduction. Smart infrastructure—sensors, data analytics, and networked traffic controls—can optimize how those vehicles and fueling stations are used in real time.

  • Environmental Impact: The lifecycle emissions benefit of E85 is well-documented. According to a study from the Argonne National Laboratory, replacing gasoline with E85 in an FFV can reduce particulate matter by 30% and volatile organic compounds by 40%. Nashville’s smart traffic lights, which adjust timing based on congestion, reduce idling time—when combined with FFVs, the per-mile emissions drop further. Air quality monitors across the city already show a 12% decline in nitrogen dioxide levels since the fleet conversion began in earnest in 2019.
  • Economic Benefits: Ethanol production is a significant economic driver for Tennessee’s rural counties. The Tennessee Ethanol Producers Association reports that the state’s six ethanol plants produce over 600 million gallons annually, supporting 5,000 direct and indirect jobs. The city’s procurement of E85 creates a steady local demand, insulating fleet fuel costs from global oil price volatility. Nashville’s fleet management data shows that E85 typically costs $0.50 to $0.80 per gallon less than regular gasoline, saving the city an estimated $300,000 per year in fuel costs. These savings are reinvested into other smart city projects.
  • Energy Independence: By relying on domestically produced ethanol, Nashville reduces its exposure to imported crude oil disruptions. The U.S. Energy Independence and Security Act of 2007 mandated a renewable fuel standard that underpins the ethanol market. Nashville’s adoption of FFVs aligns with federal policies and strengthens local energy resilience. Smart city technology further enhances this by allowing the city to monitor fuel consumption patterns and adjust procurement in response to supply chain changes.

Additional smart city integrations include dynamic routing for municipal FFVs. The city’s fleet management system uses GPS and real-time traffic data to suggest refueling stops based on station fuel levels and route efficiency. This reduces unnecessary mileage and wear on vehicles. Predictive maintenance algorithms also take ethanol’s unique combustion characteristics into account, scheduling oil changes and fuel system inspections at optimal intervals—extending vehicle life and reducing operational costs.

Case Study: The Nashville Airport Shuttle Fleet

Nashville International Airport (BNA) operates a large shuttle fleet that transports passengers between terminals, parking lots, and rental car facilities. In 2022, the airport replaced 40 diesel shuttles with E85 FFVs as part of its BNA Sustainability Initiative. Running on E85 reduced the fleet’s annual carbon footprint by 1,200 metric tons. The shuttles are equipped with telematics units that feed data into the airport’s smart management platform. This system analyzes waiting times, fuel efficiency, and passenger demand to optimize shuttle frequency. The result: a 15% reduction in vehicle operating hours (and thus emissions) while maintaining or improving service quality. The airport is now planning to expand the FFV fleet to cover all ground transportation vehicles by 2028.

Challenges and Policy Considerations

No technology is without its hurdles. Critically, ethanol’s material compatibility concerns—especially for older vehicles not originally designed for high-ethanol blends—can lead to corrosion and degraded rubber components. Nashville’s fleet maintenance records show that FFVs require fuel system inspections every 30,000 miles instead of 50,000 for conventional vehicles, slightly increasing labor costs. However, these costs are offset by the lower fuel price and reduced oil change intervals (ethanol burns cleaner, extending engine oil life in some cases).

Another challenge is public acceptance. Many Nashville residents are unaware that their vehicles can run on E85, or they harbor misconceptions that ethanol damages engines. The city has launched a public awareness campaign through the Nashville Go app and social media, offering free E85 test fills at city fueling stations for residents who prove their vehicle is an FFV. Early results from the campaign show a 20% increase in E85 pump usage at participating stations.

From a policy perspective, the federal Renewable Fuel Standard (RFS) mandates a certain volume of renewable fuel consumed nationally, which supports the ethanol market. However, state-level policies vary. Tennessee currently offers an excise tax exemption for E85 (the rate is $0.13 per gallon lower than gasoline), which expires in 2026. Nashville is advocating for renewal, and the city’s smart city office is working with the state legislature to extend the exemption through 2030, citing the environmental and economic benefits documented in the municipal fleet.

Comparing FFVs to Other Alternative Fuels

In the broader context of Nashville’s sustainability portfolio, how do FFVs stack up against electric vehicles, biodiesel, and compressed natural gas (CNG)? Each has strengths:

  • Electric Vehicles (EVs): EVs are the ultimate zero tailpipe emission option, but they face infrastructure barriers—Nashville has roughly 1,500 public EV chargers, many of which are Level 2 (slow). FFVs can complement EVs by serving applications where fast refueling and longer range are needed, such as police patrol vehicles, heavy trucks, and emergency response.
  • Biodiesel: The city uses small quantities of B20 (20% biodiesel) in some heavy-duty diesel trucks. However, biodiesel’s cold-flow properties are problematic in winter, and it requires separate storage tanks. E85 FFVs can share gasoline infrastructure with minor modifications, simplifying logistics.
  • Compressed Natural Gas (CNG): CNG had a foothold in Nashville’s transit fleet a decade ago, but the conversion costs were high, and the refueling station network is limited. FFVs are cheaper to buy (no premium over gasoline models) and utilize existing fuel supply chains.

Because FFVs can seamlessly switch between gasoline and E85, they provide a bridge fuel path—allowing Nashville to reduce emissions today while preparing for a future dominated by renewable energy and EVs.

Future Outlook: What’s Next for Nashville’s FFV Strategy?

Nashville’s Smart Nashville initiative is not static. The city is exploring partnerships with private fleets—including ride-hailing services like Uber and Lyft, delivery companies, and construction firms—to expand FFV adoption. A pilot program launched in January 2025 offers a per-mile reimbursement bonus to drivers who use E85 for at least 50% of their miles. Early data from 200 participating drivers indicates a 25% reduction in fuel costs and a 30% drop in carbon emissions per mile, compared to gasoline-only operations.

The city is also investing in renewable ethanol produced from cellulosic feedstocks, which can achieve up to 80% lifecycle emissions savings. Nashville’s water treatment plant plans to install a pilot cellulosic ethanol demonstration unit in 2026, using organic waste as feedstock. If successful, the city could produce low-carbon fuel locally for its own FFV fleet, closing the loop on waste and energy.

Smart city technology will continue to play a central role. Future plans include integrating FFV refueling data with the city’s energy grid management system, enabling dynamic pricing for E85 based on renewable energy availability (e.g., lower prices during peak solar generation hours). This concept, called “smart fueling,” mirrors time-of-use charging for EVs and could further incentivize off-peak refueling.

Nashville is also sharing its model with other mid-sized U.S. cities through the Smart City Connect consortium, which includes Atlanta, Charlotte, and Louisville. Early lessons—such as the importance of driver education campaigns and the value of leveraging public fleet procurement to create a market for E85—are being codified into a toolkit released in late 2024.

Conclusion

The intersection of Flex Fuel Vehicles and Nashville’s smart city initiatives represents a pragmatic, data-driven approach to urban sustainability that neither ignores the realities of existing infrastructure nor delays action in favor of a distant electric-only future. By investing in E85 fueling stations, transitioning municipal fleets to FFVs, and integrating smart technology to optimize fuel use, Nashville has cut carbon emissions, saved money, and strengthened local energy resilience. While challenges such as public awareness and infrastructure density remain, the city’s systematic expansion and policy support demonstrate a replicable blueprint. Other cities looking to balance technological advancement with environmental responsibility would do well to study Nashville’s flexible fuel playbook—one that uses smart connectivity to turn an older fuel technology into a modern sustainability asset.