Peak Flow Rate (PHF)
Calculate the peak flow rate of a roadway, q = V ÷ PHF, dividing the hourly volume V (vehicles/h) by the peak hour factor PHF (between 0 and 1, the ratio of the hour's volume to four times the busiest 15-minute volume). The result, in vehicles/h, is the equivalent flow rate of the busiest 15-minute period — always greater than or equal to the hourly volume, since traffic does not arrive uniformly. It is the design flow used in capacity and level-of-service analysis by the HCM, since sizing by the hourly average would underestimate the peaks. Enter the hourly volume and the peak hour factor.
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Taxa de fluxo de pico (FHP)
O tráfego não chega de forma uniforme ao longo de uma hora — há picos de poucos minutos em que a demanda dispara. Por isso, dimensionar uma via apenas pelo volume horário médio subestima as condições críticas. A taxa de fluxo de pico corrige isso: q = V ÷ FHP, dividindo o volume horário V pelo fator de hora de pico (FHP, ou PHF em inglês), que é a razão entre o volume da hora cheia e quatro vezes o volume do quarto de hora mais carregado. O FHP varia de 0 a 1: valores próximos de 1,0 indicam fluxo uniforme (típico de vias muito carregadas e estáveis); valores menores (0,7–0,9) indicam picos acentuados (comum em vias urbanas com variação forte). Como o FHP é sempre ≤ 1, a taxa de fluxo resultante é sempre maior que o volume horário — é a vazão equivalente que ocorreria se o pico de 15 minutos se mantivesse por uma hora inteira. É essa taxa, e não a média, que o Highway Capacity Manual (HCM) usa na análise de capacidade e nível de serviço, garantindo que a via suporte os momentos mais intensos. Informe o volume horário e o fator de hora de pico.
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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.
Saturation Flow
Calculate the saturation flow of a signalized approach, S = S₀ × N, multiplying the base saturation flow per lane S₀ (vehicles/h per lane, typically ~1800–1900) by the number of lanes N. The result, in vehicles/h, is the maximum rate of vehicles that can cross the stop line if the signal stayed green continuously and a queue existed — the queue discharge rate during green. It is a central parameter in signal design and intersection capacity, adjusted by lane width, grade, turning and parking factors. Enter the base saturation flow per lane and the number of lanes.
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.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.