Question: How does the time-segment length affect the TRANSYT 13 (or later) results? Does it have the same effect as the “simulated time period” in TRANSYT 12?
Answer: In TRANSYT 15 (and 14 and 13), the “simulated time period” is now called “modelled time period”. As you will probably know these vwersions of TRANSYT allow varying traffic conditions over time (segments) to be modelled. This means that the “modelled time period” is no longer entered directly by the user, but is simply calculated by TRANSYT as “Number of Time Segments” x “Time Segment Length”, which ARE both user-specified. The “modelled time period” works in the same way as the original “simulated time”. E.g. most of the TRANSYT outputs reflect the average (e.g. Mean Max Queue”) value over the modelled time period.
N.B. A previous TSN article (see Issue 41 – March 2007) explained how you could use the simulated time to give an estimate of the MMQs at the END of the time period rather than the average. This process is no longer necessary for this particular item, as the TRANSYT results now include an output value (see excerpt from the Link Results table: Queue and Blocking below) called “Mean Max Queue EoTS”. EoTS stands for “End of Time Segment”. Obviously when you have just one segment, this value is also the MMQ at the end of the modelled time period. When using multiple segments there will be one for each segment.
Link Results: Queues And Blocking
|Link||Major Link||Mean Max Queue (PCU)||Mean Max Queue EoTS (PCU)|
Furthermore, please remember that most TRANSYT outputs are shown as ‘rates’ – usually per hour – and as such need to be scaled by the time-period if you wish to know absolute values for the time period being modelled. E.g. If the segment length is 30 minutes the total flows and saturation flows are entered by the user, and output by TRANSYT as hourly values. To work out the total flow over a stopline during a 30 min segment, you will need to divide the results by two. However, even when segment lengths are fractions of an hour, it is normally easiest to continue to work with rates throughout rather than absolutevalues.