6.5 GapModel
The gap acceptance model in MITSIMLab is probabilistic, where the available gaps are compared against the critical gaps. The model defines the lead and lag gaps as the clear spacing between the subject vehicle and the lead and lag vehicles in the adjacent lane, respectively. A gap is acceptable only if the lead and lag gaps are acceptable (i.e. available gap ≥ critical gap). Critical gaps are assumed to be log-normally distributed, where the mean is a function of explanatory variables, which include the relative speeds of the lead and lag vehicles. The drivers that cannot change lanes immediately select a short-term plan to perform the desired lane change. Short-term plans are defined by the various traffic gaps in the target lane. The target gap choice probabilities are modeled with an MNL structure where the trade-offs among different attributes of the gap (e.g. gap size, distance to the gap etc.) are accounted for (Ben-Akiva et al., 1999).
The chooseTargetGap function makes the choice of the target gap (forward, backward or adjacent) depending on the gap utilities. The function does not output any value but updates the value of the `STATUS variable with the chosen target gap.
where dis is the gap distance, dx_gap is the distance to gap, dv is the relative speed, δ^hv is a dummy variable accounting for the presence of an heavy vehicle (1 if vehicle on TL is heavy, zero otherwise), rand a normal random number, and β0, β1, β2, β3, β4 and β5 are fixed parameters defined in the same file (see Section 6.6). The computation of the variables used in the above equation depend on the relative position of the vehicles on the current and target lane.
Flowchart for choosing target gap
The critical gaps are calculated using the function lcCriticalGap.
Flowchart for calculating critical gap
The critical gap (Grcritical) is first computed using the following equation:
where ΔV is the speed difference between the subject vehicle and the lead/lag vehicle on the target lane. The parameters of the above equation are different for the lag and lead gaps. All needed parameters are specified in the parameter configuration XML file (see Section 6.6).
- Ben-Akiva, M. E., Koutsopoulos, H. N., Toledo, T., Yang, Q., Choudhury, C. F., Antoniou, C., Balakrishna, R. (2010) "Traffic Simulation with MITSIMLab". Fundamentals of Traffic Simulation, International Series in Operations Research & Management Science, Volume 145 2010, Jaume Barceló (Eds.), ISBN: 978-1-4419-6141-9