LASER 3.1 Update

Executive Summary

In 2005, the Department appointed Mott MacDonald (Motts) to update the LASER 3.0 land use/ transport interaction model base year to Census 2001 and to carry out a number of model tests. The purpose of this project was to produce a present day model validation. Any model re-calibration was outside the scope of this work. The new model is referred to as LASER 3.1.

The London and South East Region Model (LASER) is an integrated land use and transport model for a study area that covers Greater London, and two UK Government Office Regions around London. The area as a whole, often referred to as the ‘South East’ in the UK, has around 20 million inhabitants and 10 million employed and self-employed workers. The LASER model is an attempt to depict the basic land use and transport processes of the region, and is intended to be used as a platform for assessing a range of policy measures that aim to transform land use and transport.

The LASER3.1 model validation was undertaken by comparing model outputs against observed data. This was done on an aggregate level for the whole study area, and at a slightly more detailed level focusing on two small parts of the model, namely London Docklands and the M23 corridor, where significant land use changes have taken place in the last few years.

At the start of this project, WSP (who undertook work on previous versions of LASER model
development), provided Motts with LASER 3.0 files. It was noted that there were differences between LASER 3a and LASER 3b input files. Version 3a is the original model and version 3b is a revised model which formed the basis of published work on Thames Gateway and the Wider South East Study. Motts were commissioned to investigate and to report on the differences between these model versions. The consultants noticed that between versions 3a and 3b, there was an increase in modelled highway flows leading to a significant deterioration in the validation. It was not possible to identify precisely what effect each of the changes between 3a and 3b had on these flows, but the two most likely candidates were, updated land-use inputs and improved convergence. Although these two factors initially seemed the most likely reasons for the change in flows, they only explained part (or
most half) of the increase. The number of land-use/ transport model loop between versions 3a and 3b increased from 2 to 3 cycles. Overall, most changes between 3a and 3b can be considered improvements to the model.

The results of the revised (LASER 3.1) land use model showed the total modelled number of
households in each zone was a reasonable fit to the Census, but the fit was poorer when looking at different types of household. The estimation of the location of retail employment was generally poor, the commuting trip length distribution appeared reasonable and there were some small differences between the modelled production-consumption matrix for workers and Census journey to work data.

The outputs of the transport model showed car mode shares were overestimated for commute trips and underestimated for other purposes. However, taken over all purposes, there was a reasonable match between modelled and observed mode shares in each region. Road flows were significantly overestimated on almost all cordons and screenlines and rail flows were significantly underestimated on a cordon of central London stations. Comparison of 1997 and 2001 flows with 1991 results suggests that there might be a tendency for LASER 3.1 to overestimate rates of traffic growth over time.

The validation was worst for link flows, which appeared to be a result of a combination of the land-use and transport components of LASER 3.1. Although, a strategic model such as LASER cannot be expected to validate well at an individual link level, the main concern is related to the scale of the differences between modelled and observed flows for total flows across cordons and screenlines.

LASER 3.1 Update (2 Mb)

LASER 3.1 Update Report is about a study that the Department commissioned to Mott MacDonald (Motts) in 2005, to update the London and the South East Region (LASER 3.0) land use/ transport interaction model base year to Census 2001 and to carry out a number of model tests. The purpose of this project was to produce a present day model validation. Any model re-calibration was outside the scope of this work. The new model is referred to as LASER 3.1.

Published:

01 July 2008

LASER Comparison of 3a and 3b (516 kb)

LASER Comparison 3a and 3b Report is about investigation into the differences between LASER 3a and LASER 3b. 3a and 3b refer to different versions of the LASER 3.0 1997 model. Version 3a is the original model and Version 3b is a revised version of the model which formed the basis of published work on Thames Gateway and the Wider South East Study.

Published:

01 July 2008