traffic beam
A headlight setting intended for roads with traffic on them at night.
traffic beam: low-beam headlight for oncoming vehicles
A traffic beam is a headlight mode designed to illuminate the road ahead without dazzling drivers in oncoming vehicles. Also called dipped beam or low beam in modern usage, it directs light downward and slightly to the side, keeping the beam below the eye level of approaching cars. The term "traffic beam" reflects its specific purpose: safe night driving on roads where you expect to meet other vehicles.
On older vehicles, especially those from the 1950s through 1970s, drivers switched between main beam (high beam, for empty roads) and traffic beam using a floor-mounted dimmer switch or a stalk control. The distinction was sharper then because headlight technology was less sophisticated. Traffic beam bulbs were typically lower wattage than main beam bulbs, and the reflector geometry was deliberately designed to spread light more widely rather than throw it far down the road.
How it works and what changed
The headlight reflector or lens of a traffic beam focuses light at a downward angle, often with an asymmetrical pattern so that the right side of the road (or left side in left-hand traffic countries) receives more illumination than directly oncoming lanes. This reduces glare while still providing adequate visibility. Modern regulations specify exact beam patterns, measured in candela and lux at defined points on a test screen.
The term is now dated because headlight terminology evolved. Manufacturers and regulators shifted to calling it "low beam" or "dipped beam," and modern vehicles often have automatic headlight leveling systems and higher efficiency halogen, HID, or LED sources that perform better at all settings. Separate high and low beam reflectors became less common as multi-function optics took over.
If you encounter a traffic beam control on a vintage or preserved vehicle, expect manual switching. The beam will feel dimmer and narrower than high beam, but it should reach far enough to see obstacles 50 to 100 meters ahead at safe speeds, depending on the bulb and reflector condition. Corrosion or cloudiness inside the headlight housing degrades performance significantly on older cars.