G is for GUARD RAIL - is a system designed to keep people or vehicles from (in most cases unintentionally) straying into dangerous or off-limits areas . In traffic engineering, highway guardrail may prevent an errant vehicle from impacting roadside obstacles which may be either man-made (sign structures, culvert inlets, utility poles) or natural (trees, rock croppings), running off the road and going down a steep embankment, or veering off the roadway into oncoming traffic (commonly referred to as a median barrier). Roadside obstacles are typically referred to as fixed objects. A secondary objective is keeping the vehicle upright while deflected along the guardrail