Aurora - Dynamic trip assignment (DTA)

[Andy]

Hi all,

I have uploaded a spreadsheet (AHFC_DUE.xls) to show a simple DTA
calculation:

a. We consider a network with 1 origin-destination pair connected by 2
parallel routes:

Route 1 (e.g. a freeway):
Free flow travel time = 1.4 min
Free flow speed = 60mph
Capacity = 3600 veh/hr

Route 2 (e.g. an arterial)
Free flow travel time = 1.9 min
Free flow speed = 30 mph
Capacity = 1800 veh/hr


b. The O-D demand profile is shown on tab 'O-D demand profile' on the
spreadsheet.

c. Based on the O-D demand and the network specification, we computed
the corresponding user equilibrium assignment (tab 'DUE'). Note that
the travel time on the routes being used are equal (and less than the
unused one if any).

d. Since Route 1 has a shorter free flow travel time, traffic will
first be assigned to Route 1, and then Route 2. This reflects the
situation that drivers would first take the faster route until it is
too congested ..

e. Again, Route 1 has a larger capacity than Route 2. Route 1 will
generally carry more traffic.

f. VHT (vehicle-hour-traveled) under this UE assignment pattern is
'56.19'.

g. Consider a second scenario: suppose we impose a time-invariant toll
(which is equivalent to a travel time '0.5-min') on Route 1. Following
this, we compute a new UE assignment (see tab 'DUE_toll'). It can be
seen that the effect of such toll is to divert traffic during time
0.6(hr) - 1.0(hr) from Route 1 to Route 2.

h. The VHT under the 'tolled UE assignment' is now '49.33', given the
same O-D demand. The system appears to be improved after imposing such
toll.

i. The example above is very simple (but that's the best I can do with
the current Aurora):
1. We haven't investigated the effects of spill-back, merge, and
diverge..
2. We only consider one single O-D pair...

What I intend to show here is some numerical example of trip
assignment and some potential use of it (e.g. estimation of travel
demand and the sensitivity of it with respect to various control
policy).