I am getting conflicting information regarding the measurement of cruise time/speeds. By definition cruise times in TRANSYT are undelayed travelled times and therefore there is a tendency for cruise time measurements to be undertaken usually during off peak periods (early morning or late evening) when there is virtually very little traffic on the network. However, as a result, measurements made at these times do not reflect existing traffic conditions.
The problem I think is the interpretation of what represents undelayed travel time. Does undelayed travel time represent free flow under existing traffic conditions (even in peak traffic conditions) where there are no delays due to signals or queuing traffic? Currently, I am working on a model where cruise times have been measured on a very busy link during the off peak period (when there is free flow of traffic). The proposals improve traffic flow during peak periods but no changes have been made to cruise times since this is not expected to change. There has been a suggestion that cruise time in the proposed model should be modified on account of improved traffic flow in the proposed model. Should this be the case?
Cruise times should not be changed to reflect improvements that simply reduce queueing and delay as the cruise times are already meant to represent free-flow conditions. However, if the improvements mentioned involve changes that impact on the cruise speed then cruise times should be re-measured. E.g. examples of this would be stopline-to-stopline distances changing, reduction of parked vehicles and changes in lane widths and introduction of any speed reducing features/street furniture etc. (as these all affect skin friction which affects speeds). Also changes in the mix of traffic (vehicles should be selected for measurement by a random process so that the resultant cruise speed or time reflects the mix of traffic) will have an effect.
Please note that the measurement of cruise times is best carried out during off-peak periods but should avoid very lightly loaded conditions as they will tend not to be typical.