Learn: Average time headway
Average time headway is the mean time between successive vehicles passing a fixed point in a stream. It is the time counterpart of a flow rate, not the physical gap between vehicle bumpers.
What the formula is saying
One hour contains 3600 seconds. Divide those seconds by q vehicles per hour to obtain the average seconds allocated per vehicle passage.
Read the symbols in plain language
- q
- Traffic flow
Traffic flow. The hourly units cancel, leaving the average seconds associated with each passing vehicle.
veh/hUse veh/h as the base unit shown here. q is veh/h and the result is s/veh, commonly described as seconds of average headway. A rate supplied in veh/s must first be converted or handled with the reciprocal directly.
- h
- Result to find
Average time headway. The hourly units cancel, leaving the average seconds associated with each passing vehicle.
s/veh
Sort out the units first
q is veh/h and the result is s/veh, commonly described as seconds of average headway. A rate supplied in veh/s must first be converted or handled with the reciprocal directly.
Assumptions before calculating
Assume a positive, representative flow rate for a defined stream and observation interval. Interpret headway between the same vehicle reference points, such as front-to-front passages.
Let’s solve one together
Read the given values, follow each operation, then check what the result means.
Read the supplied values as one complete study case. Find h and explain the result in the stated output unit.
- q · Traffic flow
- 1800 veh/h
Express one hour in seconds
An hour contains sixty minutes of sixty seconds each.
3600 = 3600 s/hDivide available time by passage rate
The hourly units cancel, leaving the average seconds associated with each passing vehicle.
(3600) ÷ (1800) = 2 s/veh
Does this worked answer make sense?
A flow of 1800 veh/h gives 2 s/veh. Doubling flow halves average time headway, within the interpretation of the same traffic stream.
A second worked example — different values
A second case uses different data. Predict which way the answer will change, then calculate it without reusing the first answer.
- q · Traffic flow
- 1200 veh/h
Express one hour in seconds
An hour contains sixty minutes of sixty seconds each.
3600 = 3600 s/hDivide available time by passage rate
The hourly units cancel, leaving the average seconds associated with each passing vehicle.
(3600) ÷ (1200) = 3 s/veh
Now try your own values
Change a value or its unit. The same method will show your calculation, step by step.
Results update only when you calculate. The lesson example above stays unchanged.
Your turn — check your understanding
Solve this separate case yourself. Use only the values below; the two worked examples use different data. Give the requested result in the selected unit.
- q · Traffic flow
- 2400 veh/h
Find: Learn: Average time headway
A hint, not the answer
One hour contains 3600 seconds. Divide those seconds by q vehicles per hour to obtain the average seconds allocated per vehicle passage.
q is veh/h and the result is s/veh, commonly described as seconds of average headway. A rate supplied in veh/s must first be converted or handled with the reciprocal directly.
Show the full practice solution
Compare the steps with your work; revealing a solution does not mark the lesson complete.
Express one hour in seconds
An hour contains sixty minutes of sixty seconds each.
3600 = 3600 s/hDivide available time by passage rate
The hourly units cancel, leaving the average seconds associated with each passing vehicle.
(3600) ÷ (2400) = 1.5 s/veh
Avoid the common trap
Do not multiply by q or use 60 seconds per hour. Do not subtract vehicle length from a time headway; vehicle clearance is a different quantity.
When this method applies — and when it does not
This is an average implied by the rate, not every individual headway and not a recommended safe following time. Combined multi-lane flow gives a combined-stream passage interval, not automatically a single-lane following headway. At zero flow a finite mean headway is not defined.
For study and understanding, not approval of a real structure, site operation or design. Apply the correct standard, National Annex and professional review to actual engineering work.
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Sources & further reading
References open in a new tab and explain the underlying principles. The teaching text and examples here are SimpleFlick’s own; the source organisations have not endorsed this calculator.
Reading focus: Average time headway. Consistent traffic density, flow and space-mean speed; headway follows from vehicles per unit time and is not the clear following gap.
Lesson updated: · Both examples and the separate practice case are checked against an independent high-precision numerical implementation. This verifies arithmetic for the stated model, not engineering certification.