CTM_C_Program

Implementation of CTM by C++ Language

lane-intersection structure

The previous version builds the model directly on the cell-link level, which makes it hard to scale. To solve it, the new version will focus on the lane-intersection level. During the operations on the lanes and the intersections, the related cells and links are automatically created or modified.

Another difference with the previous version is that the access field is transferred from cell to link, so that the model can handle more complicated phases.

lower-level

Data Structure

cell struct	description
type:int	type of cell (normal;input;output)
rate:double	saturated flow rate (veh/s)
cap:double	capacity (veh)
length:double	current number of vehicles within (veh)
delay:double	accumulated vehicle delay (veh*s)

link struct	description
type:int	type of link (direct;merge;diverge)
cells:int[3]	indices of two or three cells
ratio:double	merge or diverge ratio [0,1]
access:bool	availability of the link

data lists:

name	description
list_cells	list of all cells
list_links	list of all links
list_pos_in	the possible inputs of all cells
list_pos_out	the possible outputs of all cells
list_in	the real inputs of all cells
list_out	the real outputs of all cells

Simulation Procedure

• Step 1: list_cells --> list_pos_in, list_pos_out

  calculate the possible inputs and outputs of all cells

• Step 2: list_pos_in, list_pos_out, list_links --> list_in, list_out

  calculate the real inputs and outputs of all cells

• Step 3: list_cells, list_in, list_out --> list_cells

  update the lengths and delays of all cells

Data Model: Lane-Intersection

Lane

property	description
type:int	type of lane (normal;entry;exit)
cap:double	capacity (veh)
sat_rate:double	saturated flow rate (veh/s)
in_rate:double	input flow rate (veh/s)
out_ratio:double	the ratio of output vehicles due to all input ones [0,1]
in_cell:int	index of the input cell
out_cell:int	index of the output cell
o_cell:int	index of the origin normal cell
d_cell:int	index of the destination normal cell
in_link:int	index of the input link
out_link:int	index of the output link

Intersection

property	description
in_lanes:list<Lane*>	list of input lanes
in_cells:list<int>	list of indices of end cells of input lanes
out_lanes:list<Lane*>	list of output lanes
out_cells:list<int>	indices of begin cells of output lanes
num_cells:int	number of inner cells
cells_info:double[][2]	the information of the inner cells (cap, rate)
cells:list<int>	indices of the inner cells
phases:list<Phase*>	the information of the phases
cur_phase:int	index of the current phase

Phase

property	description
links_info:int[7]	information for the phase [type,c1_class,c1_index,c2_class,c2_index,c3_class,c3_index]
links:int[2]	indices of related links [begin,end]

Reset and add lanes

1. resetSystem

   When the system is reset, the lanes, intersections, cells and links should be all erased. All involved resources should be released.

2. addLane

   A lane is added with its type, capacity, saturated flow rate, input flow rate and output ratio.

   For the normal lane, all parameters should be specified by the caller, the capacity, the saturated flow rate are positive, the input flow rate is non-negative, and the output ratio should be inside the region [0,1].

   For the entry lane, the output ratio is always set to 0 no matter which value is given, the capacity, the saturated flow rate are positive, and the input flow rate is non-negative.

   For the exit lane, all parameters given by the caller are ignored, the capacity, the input flow rate are both 0, the saturated flow rate is infinite, and the output ratio is 1.