Back to Visual-tm home On to 2001 Census Matrix Tools We can develop a strategic multi-mode model and this sets out the nature of the model. It will be a standard four stage transport model comprising trip ends, distribution, mode choice, public and highway assignment with capacity restraint. It will use coefficients which we have from elsewhere and networks derived automatically from mapping and databases. It will have a base year and a forecast year which could be 2005 and 2011 the end of the LTP period. We will develop one future transport scenario with the client, which could be the schemes and measures in your LTP. We will run the model for the base and future scenario with and without the LTP measures. This will illustrate the effect of traffic growth by the end of the LTP period and the effect of the LTP measures on the traffic growth.
The complete model would be mounted on your computer with a Visual-tm software license, one years software maintenance and training for one person in how to use the model. This type of model has been used to prepare a Masterplan of Ashford and Gloucestershire’s Regional Spatial Strategy so it is tried and tested and proven to give results upon which important decisions can be made.
The model will cover both public transport passengers and highway traffic and will be strategic in the sense that it won’t contain the very local traffic movements so would not be sufficiently detailed for highway or junction design. The highway and public transport matrices would be built from your data augmented with Census Matrix Tools and rail passenger matrix data (if available). The public transport networks would be built from your ATCO CIF database. It would have 3 trip purposes and about 50 to 80 zones (so it would be a strategic model).
A study area will be defined and divided into transport zones in the area to be modelled in detail and for the surrounding external area transport zones will be larger and in less detail. A highway network will be coded so that it is consistent with the zone system and carry inter-zonal traffic. For most study areas the highway network will include the major roads (Motorways and A roads) and some of the minor (B roads). The public transport network comprising the bus and rail routes in the study area will be derived from the ATCO CIF files (or TransXchange if in London) and as these files are prepared by the Local Authority, we are assuming that they are accurate.
The model will comprise the following components:
- A highway network coded as nodes (at junctions), links (to represent the roads between junctions), and turn penalties. Roads will be classified according to the standard classification for speed/ flow curves and standard speed/ flow curves allocated to links. Junction detail will not be coded (although it could be added later if needed).
- A public transport network comprising routes, services, bus stops and railway stations. Interchange detail will not be coded (although it could be added later if needed).
- An all-day distribution model which will take the base year or 2011 forecast trip ends for three purposes: car available work, car available other, non-car available and distribute them according to the logsums (see below) to produce three (ie by purpose) all-day all-mode trip matrices which will then be supplied to the mode choice model.
- A mode choice model which will take the three purpose trip matrices from the distribution model and split each of them into two modes: private and public travel. It will also take skims from the highway and public transport networks and produce an all-mode logsum for the distribution model, which represents the separation between the zones.
- A morning peak highway assignment model which converts the matrices to morning peak car driver trip matrices and assigns them to the network. The assignment will use capacity restraint iterations so that speeds match the traffic volumes.
- An all-day public transport assignment. If there is more than one public transport mode (eg bus and train) then the sub-mode choice will be done by the assignment procedure.
- The model will be iterated through the major supply/ demand loop comprising the components 3,4 and 5, will calculate new speeds from 5 which are input to the start of the next iteration. The major iterations will be repeated until supply/ demand equilibrium has been reached. This will use our four stage model engine and be run automatically. The model generally converges in about 4 major iterations each one having 40 iterations of capacity restraint and run time is estimated to be a few minutes.
For scenario testing model runs, we will prepare the following:
- Trip generations and attractions will be prepared for the base year (eg 2005) and one forecast year (eg 2011) would be developed from Tempro for each of the three trip purposes.
- One forecast network scenario would be coded in conjunction with the client to represent the likely future highway and public transport network in 2011. This could comprise the 2011 LTP and other schemes.
Three model scenario runs will then be undertaken as follows:
- The Base: The base year network with the base year matrix so as to represent the current situation
- The Forecast Do-Nothing: The forecast year matrix with the base year network to represent what would happen if the highway and public transport system remained unchanged. This will illustrate the scale of extra congestion forecast in the future year (eg 2011)
- The Forecast Do-Something: The forecast year matrix with the forecast network scenario. This will illustrate the effect of the LTP and any other road and public transport improvements, on the levels of additional congestion found in 2 above.
The Results from these model scenario runs will give the level of traffic on each road in the network in the base (ie 2005) and in the future (ie 2011). It will show the relative levels of congestion on the road network (local traffic will not be in the model so the traffic volumes are unlikely to be sufficiently detailed for designing junctions etc). The model will output the mode shares (ie the proportion of car travel) so you can see if your LTP will switch car drivers onto public transport and reduce congestion. It will output the passenger volumes on the bus and train routes coded into the model but the degree of precision will depend upon the quality and detail in the origin-destination data. As bus origin-destination data is generally sparse the forecast public transport passenger volumes are likely to be useable as relative values (eg bus passengers on this corridor grow by x% and with the LTP they increase by y%). You can then use the model to investigate the effects of different LTP measures on congestion, mode shares etc.
The level of detail that the strategic multi-mode model can be used for, would depend upon the study area to be modelled, the quality of the data used to build the origin-destination trip matrices and on how fine the zone system is. The model would be capable of being refined later with a finer zone system and finer networks with junction details in which case the matrices can be re-built to include local traffic. In this case the refined model can be validated to DfT/ HA standards and be used as part of the highway design process. The model refinement can include more modes (eg cycle, park & ride) more detailed purposes (eg school, business), more detailed treatment of parking (eg short/ long stay or free parking), local coefficients and different times of day (eg evening/ off peak) and be linked to the appraisal process for major Scheme Bids (eg TUBA). This is one of the best ways of getting a detailed multi-mode model and has been used on a number of studies including for Gloucestershire where the Regional Spatial Strategy model was enhanced for their Major Scheme Bid Model and interfaced to their SATURN highway assignment model so that Visual-tm did the public transport and multi-mode modelling and SATURN provided the highway assignment.
Back to Visual-tm home On to 2001 Census Matrix Tools