CSIM Scenarios

A note about "boxes"
A CSIM scenario consists of three parts: set up; execution; and analysis.

Set up
The set-up begins with the entry of parameters into text files off line. CAVWAY parameters include CAVWAY-grid geometry, traffic speed in each lane, node locations, and inter-CAV spacing. Scenario parameters include traffic and message-update intervals, and various time limits. Prior to execution, CSIM checks parameter validity. For example, CSIM does not allow the speed in any two adjacent lanes to be equal since that might prevent run-time lane changes.
Once run-time parameters have been verified, CSIM establishes a route, a series of CAVWAY segments from each node to every other node. CSIM builds a route table which includes the first segment of each computed route for every pair of nodes in the CAVWAY grid.
The traffic-update-interval, is used to schedule periodic events. The user may also request that CSIM schedule random events, such as CAV malfunctions, to exercise and evaluate emergency responses. Random events may be specified using Excel spreadsheets: each random event specification includes an event type and values to bound the (simulation) time within which the event will occur.
Boxes
CSIM uses boxes to designate roadway units and enforce CAV spacing. CSIM implements platooning using boxes traveling at constant speeds and spacing within each lane; each box is either empty or occupied by a single CAV. A critical experiment may be necessary to determine the CAV spacing needed to provide adequate margins of safety on CAVWAYs which comply with curve and grade standards. CSIM will ultimately use box sizes consistent with critical experiment results. CSIM trials have already shown that, regardless of box size, this approach to platooning would accommodate necessary lane changes when traffic was within corridor capacity.
Execution
Execution is the running of a CSIM scenario. To model the movement of traffic, CSIM performs the following steps periodically to update the position and status of each CAV on a CAVWAY:
  1. Remove exiting CAVs and move transferring CAVs to new CAVWAYs;
  2. Allow CAVs to make pending lane changes that (they determine) can be performed safely;
  3. Advance CAVs on CAVWAYs at the respective lane speeds;
  4. If a CAV has reached the node at the end of a segment and that node is the final CAV destination, have that CAV exit;
  5. If a CAV has reached the node at the end of a segment and that node is not the final CAV destination, retrieve a new first segment from the route table between the node just reached and the destination;
  6. Assess access demand and traffic load at each node in each direction – enter queued CAVs onto the corridor as loads permit;
  7. Mark exiting or transferring CAVs for lane changes, accounting for blockages, detours, and merges;
  8. Alter user fees as indicated by a fee computation algorithm; and
  9. If the clock has reached the simulation-time-limit, halt execution; otherwise, schedule the next traffic update (at current-time + traffic-update-interval), advance the clock to the next scheduled event, and perform that event.
During execution, result values are written to various Excel™ tables.
Analysis
Following execution, the user may examine and display selected Excel results to observe whether and how well algorithms are working. Reality checks on the effectiveness of congestion pricing will require critical experiments.
A box, as described at left, is a software construct to facilitate characterization. Any actual implementation of a CAVWAY may or may not find such a construct useful.