A. Spiliopoulou^a,
M. Kontorinaki^a,
M. Papageorgiou^a,
P. Kopelias^b


Highlights

•Comparison of two traffic flow models, namely the CTM and the METANET model.
•The models are calibrated and validated using real traffic data.
•The models aim to reproduce traffic congestion due to a saturated freeway off-ramp.
•The validation results show that both models can reproduce the traffic conditions.
•METANET offers a more accurate representation of the prevailing traffic conditions.


Keywords
Macroscopic traffic flow models; Model validation; Freeway off-ramps



Abstract
The reported study tests, validates and compares two well-known macroscopic traffic flow models in the special, but quite frequently occurring case, where congestion is created due to saturated freeway off-ramps. In particular, the comparison includes the first-order model CTM (Cell Transmission Model) and the second-order model METANET. In order to enable a reliable and fair comparison, the traffic flow models are first calibrated by use of real traffic data from Attiki Odos freeway in Athens, Greece. The resulting models are validated using various traffic data sets, different than the one used for their calibration; the models are then evaluated and compared with respect to their accuracy in the reproduction of congestion created at freeway off-ramp areas.



Article Outline
1. Introduction
2. Macroscopic traffic flow models
2.1. CTM (Cell Transmission Model)
2.2. METANET

3. Macroscopic traffic flow model calibration and validation
4. Test network and traffic data
5. Calibration and validation results
5.1. Calibration results
5.2. Validation results and model comparison

6. Conclusions
Acknowledgements
References



Figures
   

Fig. 1.

(a) Fundamental diagram within CTM; (b) freeway discretization.


Fig. 2.

Model calibration procedure.


Fig. 3.

Representation of the considered Attiki Odos freeway stretch.


Fig. 4.

Time–space diagram of measured speed at the considered freeway stretch for four different days.


Fig. 5.

Nelder-Mead algorithm convergence during the calibration of: (a) the CTM and (b) the METANET models.


Fig. 6.

Space–time diagram of measured speed and the CTM model estimation for 16/06/2009.


Fig. 7.

Time-series of the real speed measurements and the CTM model estimation of speed at various detector locations for 16/06/2009.


Fig. 8.

Space–time diagram of real speed and the METANET model estimation for 16/06/2009.


Fig. 9.

Time-series of the real speed measurements and the METANET model estimation of speed at various detector locations for 16/06/2009.


Fig. 10.

Space–time diagrams of measured speeds and the models’ estimation for 26/05/2009, 23/06/2009 and 25/06/2009.




Tables

Table 1. Optimal parameter values for the CTM model.

Table 2. Optimal parameter values for the METANET model.

Table 3. Performance index for the whole network and per network link for the CTM and the METANET model for all investigated dates.