• ‘Total delay’ to ‘volume of traffic’ ratio: Gives the ‘‘average amount of delay’’
for a vehicle travelling 1 km.
• Speed-based KPIs, especially relevant for motorways (e.g., a congested state
exists when traffic speed is below 70 kph).
• The ‘congestion reference flow’, an index determined by capacity of the road,
number of lanes, and other traffic-related variables.
• The ‘level of service’ indicator, a basic congestion scale running from A to F
(with A being best) that describes conditions using variables such as speed,
travel time, disruption to flows, and safety. It is widely employed in the United
States.