DCE evidence in transport cost-benefit appraisal

Transport infrastructure decisions worth billions depend on DCE-derived estimates of the value of travel time.

This article explains how DCE evidence - value of travel time, value of reliability, mode shift probabilities - is integrated into transport cost-benefit appraisal frameworks such as WebTAG.

Ben White, 07.07.2026

How DCE evidence enters transport appraisal

Transport infrastructure decisions - whether building a new motorway, extending the underground, or investing in bus rapid transit - are evaluated using cost-benefit analysis. The benefits side of the CBA is dominated by time savings: the value of the travel time that users save because of the infrastructure investment.

These time savings are valued using the value of travel time (VoTT) - a unit rate derived from DCE stated preference studies. The quality of the CBA benefit estimates therefore depends directly on the quality of the underlying DCE study. An underestimated VoTT understates benefits and may cause a socially valuable investment to fail the appraisal. An overestimated VoTT leads to over-investment.

How WebTAG and equivalent frameworks use DCE evidence

WebTAG (the UK Department for Transport's Transport Analysis Guidance) specifies official VoTT values derived from stated preference research. These values are updated periodically - the most recent major update used data from a large-scale national SP survey. Local and project-specific transport studies may use their own SP-derived VoTT estimates but are required to justify any departures from WebTAG values.

Beyond VoTT, transport CBAs increasingly use DCE-derived estimates of the value of reliability (the WTP for a reduction in journey time variability), the value of crowding reduction, and the value of information provision. All of these are estimated from SP studies using SurveyEngine's stated preference survey platform.

Mode shift modelling - estimating how many existing travellers will switch to a new transport option - also uses DCE-derived parameters, typically from logit models estimated on combined RP/SP data.

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Integrating DCE evidence into your transport appraisal

Step 1: Identify which DCE-derived values you need. For a standard transport CBA, you need VoTT by trip purpose (business, commuting, leisure), value of reliability, and potentially value of crowding or information. Identify gaps where your study needs to provide evidence not available from national surveys.

Step 2: Estimate VoTT using a joint RP/SP model. Use SurveyEngine's combined RP/SP survey to collect both revealed and stated preference data, and estimate VoTT using a joint RP/SP model in Apollo. This produces more reliable VoTT estimates than SP-only models.

Step 3: Compare against national benchmarks. Before using your estimates in the CBA, compare them against WebTAG (UK) or equivalent national values. Explain any significant differences in terms of sample characteristics, corridor context, or study design.

Step 4: Calculate benefit streams for the appraisal. Apply VoTT estimates to the projected time savings across all user segments. Combine with reliability and other values to produce total user benefit estimates in present value terms.

Step 5: Present sensitivity analysis on VoTT. CBAs based on DCE evidence should include sensitivity analysis on VoTT - testing the BCR at WebTAG values, at your estimated values, and at values 20% above and below your estimates. This is required by WebTAG for studies that deviate from official values.

Worked example - BRT corridor CBA

A bus rapid transit corridor study estimates VoTT of £9.40/hour for commuting (vs WebTAG £9.90/hour) and £7.20/hour for leisure (vs WebTAG £7.50/hour). The 5% departure from WebTAG values is within the acceptable range and is explained by the corridor's lower-income demographic profile.

The CBA uses these values to calculate annual time saving benefits of £24.3M. Including value of reliability (£3.2M) and crowding reduction (£1.8M) gives total annual user benefits of £29.3M. Present value over 30 years at 3.5% discount rate: £507M. Capital cost: £280M. BCR = 1.81. The scheme passes the DfT's investment threshold.