Issues:
1. An arterial model should provide the following:
a) Travel times
b) Delay
c) Stops
d) Volumes
e) Queues
f ) Cycle failure
g) Oversaturation
2. An arterial model should have control settings for coordinating ramps and arterials.
3. Can our arterial model be used for trip assignment?
a) What demand format (e.g. in form of O-D tables, turning ratios, etc) does the model accept?
4. Can the model be calibrated with counts/turning movements?
Outcomes (regarding point 1 above):
1. Travel time should refer to actual travel time, instead of instantaneous one.
2. Individual travel time for each vehicle can be determined by cumulative traffic curves.
3. Delay is determined as the difference between the actual travel time and the free-flow travel time. The free flow travel time of a link is defined as the time taken by a vehicle traveling through at free flow speed. The free flow speed of arterials is taken as 25 mph – 30 mph.
4. There is some discussion on the definition of ‘zero delay’. It is raised that ‘zero delay’ may be meaningless as all vehicles will definitely incur some delay on arterial. It is suggested that ‘zero delay’ should refer to the minimum delay that we can get in the arterial network.
5. The number of stops is generally defined as the number of times found that a vehicle is travelling less than a predefined speed threshold (typically 5 mph).
6. In macroscopic model (like Aurora), the number of stops can be approximated by the number of vehicles queued up during a red phase.
7. Cycle failure refers to the situation when vehicles arrived during the red phase of a cycle cannot be completely discharged by the end of green.
8. Oversaturation refers to the situation when a vehicle cannot proceed to the downstream even when the signal is green due to the spilling back of downstream queue to the local intersection.
9. Oversaturation can be detected in Aurora-CTM by checking when the ‘third term’ in the cell transmission rule dominates.
10. There are a number of different definitions for the terms ‘Cycle failure’ and ‘oversaturation’ in the literature. Some of them refer these two terms to the same thing. We shall follow the definitions adopted in Highway Capacity Manual.
1 comment:
Some further points that we may need to think of:
1. Do you think if it is a good idea to build a Paramics microscopic model of the same arterial as well? We can then do some comparison between microscopic and macroscopic models for arterial modeling purpose. Do you think it will take a lot of time and effort to make a Paramics model?
2. What should be the ‘objective function’ when we do the calibration? Delay/ travel time? If so, Aurora need to be enabled to calculate the ‘actual travel time’ for each ‘vehicle’ along links/routes.
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