What do L3 and L4 mean in cars?

[McSebastian]

Engine L3 refers to an inline 3-cylinder engine, while L4 refers to an inline 4-cylinder engine. Here is the relevant information: 1. Inline Engine (Line Engine): All its cylinders are arranged side by side in a single plane. Its cylinder block and crankshaft structure are simple, and it uses a single cylinder head, resulting in lower manufacturing costs, high stability, good low-speed torque characteristics, low fuel consumption, and compact size, making it widely used. The disadvantage is lower power output. "Inline" can be represented by the letter L, followed by the number of cylinders to form the engine code. Modern cars mainly feature L3, L4, L5, and L6 type engines. 2. Engine: An engine (Engine) is a machine that converts other forms of energy into mechanical energy, including internal combustion engines (such as gasoline engines), external combustion engines (such as Stirling engines, steam engines), and electric motors. For example, an internal combustion engine typically converts chemical energy into mechanical energy. The term engine can refer to both the power-generating device and the entire machine including the power unit (e.g., gasoline engine, aircraft engine).

[LaLily]

I've been driving for over a decade and witnessed autonomous driving evolve from sci-fi to reality. Level 3 autonomy means the car can drive itself under specific conditions like highways, but requires human intervention when issues arise—you can't completely zone out. Level 4 is far more advanced, enabling fully autonomous operation within defined areas such as city centers or industrial parks, essentially providing a robotic chauffeur. However, most vehicles on the road today still feature Level 2 driver assistance, with true Level 3 only experimentally available in a few luxury models. Level 4 is primarily used in closed environments like campus shuttles. The day Level 4 taxis dominate the streets, getting a driver's license might become obsolete.

[LaEvelyn]

From a technical perspective, the key difference between L3 and L4 lies in system takeover capability. L3 requires human readiness to take over at any moment, like a coach sitting in the co-pilot seat; L4 can achieve fully unmanned operation within limited areas (geofenced zones). During testing, we've seen L4 prototype vehicles autonomously identify construction cones and stray cats, with response speeds three times faster than humans. Beijing's Yizhuang autonomous taxis in China are approaching L4 level, though current regulations still require a safety officer in each vehicle. Personally, I find highway L3 functionality most practical for reducing fatigue during long-distance driving.

[DiWillow]

From a safety perspective, the biggest difference between L3 and L4 lies in liability attribution. In L3 vehicles, drivers are responsible for accidents because the system requires them to be ready to take over at any time. However, in L4 vehicles operating in autonomous mode, the automaker bears full responsibility for accidents. A certain German brand has equipped its L3 functionality with eye-tracking to ensure driver attention, while L4 test vehicles are all equipped with quintuple braking systems. Each level increase in autonomous driving can reduce accident rates by 70%. However, in heavy rain, all systems may fail, and human intervention becomes necessary.

[MackenzieLynn]

In future applications, L3 is suitable for private car owners to use during highway commutes, allowing them to take their hands off the wheel for ten minutes to drink coffee; L4 will completely transform transportation, such as the fully autonomous taxis currently being tested in Silicon Valley. Logistics companies are particularly eager for L4, as it would allow truck fleets to operate autonomously at night, saving on driver salaries. A friend at an autonomous driving company mentioned that their L4 system is designed to have a takeover frequency lower than the failure rate of elevators. However, the biggest bottleneck currently is not technology but regulations, as countries have strict restrictions on L4 vehicles operating on public roads.

[VanCarson]

When purchasing a smart car, it's crucial to distinguish between these two levels. Currently, genuine L3 autonomous vehicles are extremely rare in mass-produced cars, with some advertised L3 features actually being enhanced versions of L2. Meanwhile, L4 has yet to appear in regular 4S dealerships and is only being tested in specific operational zones. It's recommended to focus on the vehicle's sensor configuration: L3 typically comes equipped with 5 millimeter-wave radars plus cameras, while L4 requires lidar and high-definition map support. Don't be misled by sales jargon—models with OTA upgrade capabilities are more important, as they might unlock new features with a future software update.