PEARS: What is it?

PEARS [Program for the Economic Assessment of Road Schemes] is an economic assessment package that has been specifically designed for use with the output from traffic microsimulation models. The economic concepts in PEARS are consistent with the Fixed Trip Matrix methodologies of COBA and NESA (as detailed in DMRB Volumes 13 and 15, respectively). The methodologies and costs are derived from TAG Unit 3.5.6 - Values of Time and Operating Costs (www.webtag.org.uk).

PEARS carries out trip-based assessments of changes in travel time costs and vehicle operating costs. The costs of a trip-based assessment are derived by aggregating the costs of each individually modelled vehicle on the network.

Transport Scotland maintains PEARS and retains it as its cost benefit analysis program for use with microsimulation models. Users outside Scotland should check with the appropriate Overseeing Organisation to ensure that it is appropriate and acceptable to use PEARS.

PEARS & Microsimulation Models

Although PEARS has been specifically designed such that it can be used directly with outputs from S Paramics, it can be used with other microsimulation traffic models, providing the outputs from the models are in a suitable format for input to PEARS (which may require some element of interfacing).

The combination of microsimulation traffic modelling and PEARS provides a robust traffic and economic assessment tool in that the detailed aspects of traffic operation can be captured with greater accuracy. This includes:

• detailed network definition (e.g. hilliness and bendiness derived from OS digital mapping data, traffic calming and other localised characteristics)
• a high level of flexibility in coding and modelling the operating characteristics of different vehicle types (e.g. light, medium and heavy vehicles, public service and slow moving vehicles)
• accurate representation of the variation in traffic flows using time based profiles of travel demand by vehicle type and origin / destination (e.g. different traffic flow profiles can be used for different movements and / or directions)
• detailed modelling of individual vehicles and the interaction between cars and slower moving vehicles at junctions, in platoons, and during overtaking manoeuvres (e.g. more robust outputs for economic appraisal including the assessment of downstream benefits)