Larkhall – Milngavie Railway Project Evaluation Study Final Report

16. Appendix D: Benefit Cost Ratio Calculations

Table 51 Calculation of Rail Revenue in DM and DS
Appraisal Period Method
2006 – 2013
Do-Something LENNON outturn revenue
Do-Minimum Stations with service frequency improvement:
  • 2005 demand[56] grown in line with average annual growth at the ten Cathcart Circle stations (the control group – see section 9.17) to generate DM demand for 2006 to 2013. It is reasonable to assume that had there been no service frequency improvements then growth would have been in line with that observed on the Cathcart Circle since exogenous demand drivers are likely to have been similar for the two lines
  • Converted to revenue by using LENNON average yield data
New stations:
  • Zero demand and revenue at the four new stations but abstraction from existing stations determined using User Survey data to determine % of demand at new stations that previously accessed existing stations
2014 – 2033
Do-Something & Do-Minimum 201356 demand disaggregated by ticket type grown in line with the following drivers using an elasticity based approach as per PDFH[57] methodology:
  • Employment[58]: applied to Seasons only
  • Population58: applied to Full and Reduced only
  • GVA per capita58: applied to Full and Reduced only
  • No real fares increases assumed (assumed to grow in line with RPI from 2014 onwards)
  • Converted to revenue using 2013 LENNON average yields
2034 – 2065
Do-Something & Do-Minimum No demand or real revenue growth from 2033 onwards (in line with STAG which recommends a cap on growth beyond 2032)


Table 52 Calculation of Journey Time Savings
User Type Method
Existing rail users Stations with service frequency improvement:
  • Change in GJT in DS compared to DM calculated by applying change in service frequency penalty[59],[60],[61]
New stations:
  • Change in GJT in DS compared to DM calculated by applying change in service frequency penalty and change in assumed access time [59],[60],[61] e.g. in DM a Larkhall resident would have accessed Hamilton Central by car or bus but in DS they can board directly at Larkhall
New rail users Those abstracted from bus / car:
  • Change in GJT in DS compared to DM calculated by comparing current rail journey time to previous mode journey time[62]
  • Rule of a half applied. [41]
Those who previously didn't travel:
  • Assumed same journey time benefit as existing rail users
  • Rule of a half applied [41]


Table 53 Calculation of Marginal External Costs
Stage Description
1. Estimate change in car km
  • The difference between DS and DM demand by station calculated as per Table 51 was converted to passenger km by applying average trip length in km (assumed to be from station to Glasgow Central as user survey indicated this was the predominant destination)
  • Change in passenger km converted to change in car km by applying change in car km as % of change in rail factor (26% as per TAG guidance, Unit A5.4 Table 1)
2. Analyse characteristics of car journeys
  • webTAG provides the proportions of traffic by different road types and levels of congestion for Scotland (TAG Databook, Table A5.4.1)
  • Proportions for intervening years obtained by interpolation
  • 2006 to 2009 assumed to take 2010 values
  • 2036 onwards assumed to take 2035 values
3. Marginal external costs results
  • webTAG provides the marginal external costs in pence per km by road type and congestion band for each impact in 2010 prices (congestion, infrastructure, accident, local air quality, noise, greenhouse gases and indirect taxation)
  • These values were applied to the change in car km by road type and congestion level for each year from 2006 to 2065
4. Calculation of discounted external costs
  • The total undiscounted external costs of changes in car use over the 60 year appraisal period were discounted