TRN-32

Jam density from spacing

kj = 1000 / sj. sj is bumper-to-bumper spacing in metres, kj in veh/km.

Reading speed

TrafficJam density

Governing equation

k_j=1000/s_j

where

s_j: Jam spacing (m)
k_j: Jam density (veh/km)

Lecture brief

Historical brief

Highway and traffic theory crystallized with Greenshields’ 1935 speed–density line, then AASHTO stopping sight and equivalent axles. The lab is that operational arithmetic of flow, braking and pavement load. This sheet (TRN-32 — Jam density from spacing) is the form associated with Jam density. Working symbols: $s_j$ $\rightarrow$ $k_j$ . A parked queue occupies about 6–8 m per car. kj ≈ 125–170 veh/km/lane is the usual range.

Purpose

Purpose: compute

k_j

from

s_j

in Transport via

k_j=1000/s_j

kj = 1000 / sj. sj is bumper-to-bumper spacing in metres, kj in veh/km. Use it when a real transport question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

s_j = 7.000\,\mathrm{m}

, the governing relation

k_j=1000/s_j

yields

k_j = 142.9\,\mathrm{veh/km}

. Parked cars, a spacing, a jam density. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Jam spacing s_j7 m

Outputs

Jam density k_j142.9 veh/km

Reading speed

Watch on YouTube

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Narration of this film

Parked cars, a spacing, a jam density.

A parked queue occupies about 6–8 m per car. kj ≈ 125–170 veh/km/lane is the usual range.

Reading speed

Watch on YouTube