Question: When collecting data for TRANSYT models by what method do TRL measure on-street SATFLOWS? Or is there an industry standard method by which this is done?
Answer: Road Note 34, which describes a methodology involving recording flow rates over 6 second intervals can be used. RN34 requires a minimum of 12 seconds effective green to be useable. You may find you need to adopt a different method if saturation flow does not last very long.
An alternative is to measure all of the sat flow excluding the first two vehicles at the start of green, by simply counting the vehicles until satflow ends and then recording the length of time the recording was for. This method however has its drawbacks as it does not allow you to analyse the data for each 6- second period so you may miss the fact that you might be recoding far too long in each cycle such that the flow has dropped below satflow.
A TRL mobile software application is available that implements the RN34 methodology. This is part of TRL Mobile Traffic Apps. Please follow the link for more details.