Background

In recent years there has been increased debate at local and national level regarding the interaction between the demand for travel and our living environment. In particular there is increasing concern about the impact of the private car on our towns and cities, in terms of congestion, atmospheric pollution and associated health concerns, severance and loss of amenity, and the implications for land use policy.

Current government policy encourages local authorities to develop land use and transportation strategies that reduce reliance on the private car in favour of more sustainable modes such as bus, rail, cycling, and walking. At the same time, government planning policy guidance highlights the requirement to retain and sustain the vitality and viability of our city and town centres.

Local authorities are actively involved in implementing integrated strategies, tailored to the local context, to achieve these objectives. Successful strategies contain elements of both ‘carrot’ and ‘stick’, improving facilities and services for public transport users and non-motorised modes, whilst at the same time utilising mechanisms such as the control of parking supply and prices, and reduced highway capacity (for example through the introduction of bus and high occupancy vehicle lanes) in order to encourage modal shift. In addition, there is growing interest in the general concept of road pricing.

Transport modelling plays an important role in the demonstration of the relative merits of proposed schemes in achieving local authority objectives. Ideally a conventional four-stage strategic transport model might be used. However, the degree of complexity (and financial cost) of such models has grown in recent years in response to the demand for the capability to represent multiple modes, and to model the responses to a wide range of different policy options. Such models require large amounts of high quality travel survey data for calibration and validation, which is expensive to collect and may not always be available.

The Strategic Transport Model (STM) is a flexible multi-modal modelling tool designed to assist Town and Transport Planners in making informed and appropriate transport policy decisions for their towns and cities. STM is a highly aggregate strategic transport modelling product designed for ease of use, and with the ability to assess urban transport policy impacts rapidly with limited data requirements.

One of the main strengths of STM is its ability to provide an assessment of the potential effects of a large number of policy levers in a short timescale - it is best used for strategic policy assessment. The main characteristics of STM are as follows:

  • Highly aggregate zone structure
  • Area-wide speed flow curves
  • Rapid convergence to equilibrium
  • Rich in behavioural detail
The Strategic Transport Model provides local authorities, regional planning authorities and their agents with a means of forecasting the relative impact of various transport policy instruments, individually or in combination, in a cost effective way. The current version of STM will allow the user to assess the strategic impact of regional and urban area transport policy changes such as:

  • Road user charging
  • Parking supply and charges
  • Changes in public transport services
  • Public transport fare schemes
  • The impact of a new Park and Ride scheme
  • The impact of a new light rail scheme

STM - capabilities and limitations

STM is not intended to be a replacement for traditional, more disaggregate, network based transport models. These models will continue to have a role to play in the development and assessment of individual transport scheme options. The objective of STM is to assist planners in making informed and appropriate policy decisions for their towns and cities in a cost-effective manner.

The model is intended to be flexible, fast, and user friendly with the potential to be used by non-modellers once it has been initially calibrated for a particular location. STM allows the user to investigate a wide range of potential global and city centre policy instruments, individually or in combination, to identify what measures are most likely to be effective in the local context.

Obviously, in reducing the data requirements and cost implications relative to a traditional, more disaggregate approach, there is potential for a reduced level of absolute quantitative accuracy. The output of STM must be regarded as indicative of likely relative effects rather than as an accurate quantitative prediction. This follows from the extremely aggregate and strategic nature of the model. Nevertheless, the relative simplicity and low cost of the model is a significant benefit with regard to obtaining the appropriate data and performing sensitivity analyses. Also, the ability of STM to simulate the effects of transport choices in response to generalised cost makes it ideal for the preliminary investigation of a range of possible transport policies, provided that they operate over a spatial area approximately contiguous to at least one of the zones. It is important to note that STM is not designed or intended to assess the operation of individual transport schemes in localised spatial areas within an urban area.