TRL and John Fearon Consultancy have been commissioned by ITEA Division of the DfT to review and update the parameters used in the INCA (INcident Cost-benefit Assessment) economic evaluation software. INCA is used in the economic assessment of the affect of road schemes on the delay and journey time variability associated with incidents. Incident data for 45 weeks from December 2002 to November 2003 were available for the study. The database of incidents was compiled by a contractor, Atkins, from the police records at the Perry Barr police control centre in the West Midlands. The motorways covered include: M6 from J1 to J16; M5 from south of J8 to M6; M40 from J12 to M42; M42 from J11 to M5; M50 from M5 to A449 Ross-on-Wye; M54 from J7 to M6; M69 from J1 to M6. Four working papers have been prepared to validate and update the INCA parameters for motorways: 1. Incident rates for each link type; 2. Incident rates, ‘build-up’ duration and lane capacity factor (LCF); 3. Diversion rates and maximum delay; 4. Duration and variance weightings. Working Paper 1 (Lunt and Frith, 2004) contains a detailed analysis of incident rates, whilst the validation of incident rates conducted in this paper relates to the completeness and accuracy of the data set used for the analysis. Definitions of INCA parameters are given in Appendix A. All INCA parameters are estimated for the period 06:00 to 21:00 because the incident rates required are those which apply to any period where an incident is likely to have an effect on traffic flow. All rates and parameters are calculated for this period for consistency. This paper has been written after the checking, and if necessary correction, of the incident database. The study used incident and MIDAS data for the M6 between J4 and J10A and for the validation of the LCF only, data from the M42 J3A to J7 for the daytime period 06:00 to 21:00. MIDAS data consist of one minute average speeds and flows recorded at 500 metre intervals using inductive loops. The loops on these two sections of the M6 and M42 had been calibrated and were monitored throughout the data collection period. (Author/publisher)
Samenvatting