Hannah Clark from Devon County Council, has received this TPS  award for her paper ‘An Investigation into TEMPro growth factors’. This was one of 14 papers by young practitioners at the 2016 Transport Practitioners’ Meeting, and the competition was very strong.

Hannah’s paper investigates the performance of TEMPro growth factors, which are used to ascertain best-guess estimates of future travel demand. Confidence in the reliability of these growth factors is therefore crucial in ensuring good transport investment. Hannah’s work focused on three Devon towns (Barnstaple, Newton Abbot and Tiverton) and she undertook a retrospective analysis of the difference in TEMPro growth factors and observed growth for the period 2001-14 with TEMPro forecasts for up to 2030. Her key findings highlighted that the TEMPro growth factors appear to predict continuous growth, despite the flat observed growth profile. The TEMPro over-forecasting was such that hypothesis testing indicated the observed growth was significantly less.

Hannah then attempted to construct a predictive model which generates more realistic growth factors. Using a Generalised Linear Model (GLM) for Gamma and Gaussian distributions, a range of different models were produced and growth factors generated. These growth factors are broadly in line with the observed growth from 2010-2014, with the models demonstrating a much flatter profile than the TEMPro predictions. Growth factors were also generated for long range forecasts up to 2030. These extend the flat profiles previously generated and, should the recent trend of traffic growth continue, it could be assumed that the predictions generated in this project would be more reliable than TEMPro.

This project concludes that TEMPro growth factors are hindered by consistent over-forecasting arising from a model assuming constant growth. Strong evidence suggests this is not the trend observed in recent past across the UK. To instil confidence in practitioners who rely on these predictions, it would be prudent for other models to be investigated, such as those explored in this project.

It was the importance of this work to processes that lie at the heart of wise transport planning that led the judging panel of TPS Board members to award the prize to Hannah. In not only raising questions about the reliability of industry standard tool, one used to make major investment decisions, but also in exploring alternatives that might be better, the panel felt Hannah’s work deserved to be both recognised and better known. 

 A picture of Hannah receiving her award from TPS Board Member, Joanna Ward is shown below.

Download  a copy of her paper here   An Investigation into TEM...paper by Hannah Clark.pdf