Average Vehicle Spacing
Calculate the average vehicle spacing, s = 1000 ÷ k, dividing 1000 metres by the traffic density k (vehicles/km). The result, in metres, is the average distance between the fronts of two consecutive vehicles in a traffic stream. Spacing is the inverse of density: congested roads have high density and small spacing; free-flowing roads have low density and large spacing. It is the spatial analogue of headway (which is temporal) and relates to speed by s = v·h. The smallest spacing, at jam density, equals the vehicle length plus the minimum gap. Enter the traffic density.
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Espaçamento veicular médio
Se o headway mede o intervalo de tempo entre veículos, o espaçamento mede o intervalo de espaço: a distância média entre as frentes de dois veículos consecutivos numa corrente de tráfego. Ele é o inverso da densidade: s = 1000 ÷ k, com 1000 metros por quilômetro divididos pela densidade k (veículos/km). A relação é intuitiva — vias congestionadas têm muitos veículos por quilômetro (alta densidade) e, portanto, pequeno espaçamento entre eles; vias livres têm poucos veículos por quilômetro e grande espaçamento. Os dois conceitos, espaçamento (espacial) e headway (temporal), estão ligados pela velocidade: s = v · h. O espaçamento tem um limite físico inferior: no congestionamento total (a chamada densidade de engarrafamento, k_j, em que os veículos estão parados para-choque com para-choque), o espaçamento mínimo é igual ao comprimento médio do veículo mais uma pequena folga — tipicamente 6 a 8 metros, o que corresponde a densidades de engarrafamento de ~125–160 veíc/km por faixa. A densidade (e, portanto, o espaçamento) é a variável mais difícil de medir diretamente no campo, mas é a que melhor descreve o 'nível de aperto' do tráfego — por isso o nível de serviço de rodovias é definido pela densidade. Informe a densidade de tráfego.
Related Tools
Average Headway
Calculate the average headway (time interval between successive vehicles), h = 3600 ÷ q, dividing 3600 seconds by the flow rate q (vehicles/h). The result, in seconds, is the average time between two consecutive vehicles passing a point. Headway is the inverse of flow: the higher the traffic volume, the shorter the intervals. It is a central concept of traffic flow theory, used in signal design, capacity analysis and car-following models. The smallest safe headway defines the maximum capacity of a lane. Enter the flow rate.
Equivalent Flow (PCE)
Calculate the equivalent flow in passenger car equivalents (PCE), q = Q_cars + Q_heavy × E, adding the car flow to the heavy-vehicle flow multiplied by the equivalence factor E (how many passenger cars each truck or bus equals in road occupancy — typically 1.5 to 3.0). The result, in PCE/h, converts a mixed traffic stream into an equivalent homogeneous one, allowing volumes to be compared and the capacity of roads with different traffic compositions to be computed. Heavy vehicles occupy more space and accelerate more slowly, especially on grades. Enter the car flow, the heavy-vehicle flow and the equivalence factor.
Greenshields Speed
Calculate the speed of a traffic stream by the linear Greenshields model, v = v_f·(1 − k ÷ k_j), from the free-flow speed v_f, the current density k and the jam density k_j (vehicles/km). The result, in the unit of v_f, shows speed falls linearly with density: on an empty road (k = 0), vehicles travel at free-flow speed; as density rises, speed decreases, reaching zero at total jam (k = k_j). It is the most classic macroscopic traffic flow model, the basis of the parabolic flow-density relationship. Enter the free-flow speed, the current density and the jam density.
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