Vehicle Safety Technology Effectiveness Model

VeSTEM has been developed by TRL within the context of the revision of the General Safety Regulation and Pedestrian Safety Regulation. The model determines the cost-effectiveness of different sets of safety measures to be implemented on a mandatory basis. The combined effect of a set of safety systems may be smaller than the sum of individually predicted effects because the target populations for different systems are partially overlapping but each casualty can only be prevented once. The model allows to arrange systems into a layer structure to avoid such overestimation of benefits.

The modelled benefits (monetary values of casualties prevented or mitigated by safety measures) and costs (cost to vehicle manufacturers of fitment of safety measures to new vehicles) are compared with a baseline scenario, where none of the policy options are implemented on a mandatory basis, but voluntary uptake of safety measures continues.

Six vehicle categories (M1, M2, M3, N1, N2 and N3) are considered across a geographical scope of the entire European Union (27 Member States) and UK. The evaluation period covers 16 years to allow for a full cycle of fleet benefits to be captured. 

VeSTEM is a model to estimate the benefits (monetary values of casualties prevented by safety measures) and costs (cost to vehicle manufacturers of fitment of safety measures to new vehicles) associated with policy measures assessed in the context of the revision of the General Safety Regulation and Pedestrian Safety Regulation. The model is implemented in the programming language Python (https://www.python.org/) with inputs and outputs produced in Microsoft Excel spreadsheets.

The model considers as benefits the monetary values of casualties prevented by safety measures, and as costs the cost to vehicle manufacturers of fitment of safety measures to new vehicles. Results are benefit-to-cost ratios (BCRs), based on present monetary values and casualties prevented, compared to the baseline scenario over the entire evaluation period.

A vehicle fleet calculation module determines how the vehicle safety measures disperse into the fleet. The module determines the effect of mandating a measure for all new types, and two years later for all new registered vehicles, on the overall proportion of the fleet equipped. Benefits conferred by a safety measure, that is, casualties prevented, will only be realised by equipped vehicles. However, the legacy fleet will also be affected by active safety measures; for example, if a rear-end shunt is avoided by advanced emergency braking for driving and still-standing vehicles ahead, the vehicle in front, will benefit from the measure even if it is a legacy vehicle. This is taken into account in the benefit calculations.

To simulate the casualties prevented by each measure, an accident data analysis was performed based on Great Britain national road accident data (Stats19) to determine the casualty target population for each proposed measure (input data), i.e. the number of fatal, serious and slight injuries that could potentially be affected by a safety measure based on relevant characteristics of the collision (e.g., collision geometry or contributory factors). The target populations were scaled to EU-27 and UK level using weighting factors, based on severity and vehicle categories involved, derived from analysis of the pan-European CARE database. The target populations found are multiplied with effectiveness values for each safety measure (input data), i.e. a percentage value indicating what proportion of the relevant accidents will be avoided or mitigated by the measure. Mitigated casualties (fatal turned to serious casualty, or serious to slight casualty) are added to the target population of the next lower injury severity level for other measures. The casualties prevented are multiplied with monetary values for casualty prevention to calculate the monetary benefit.

The model also addresses the interaction of different safety measures on overlapping casualty groups. To give an example, there are collisions where a driver was exceeding the speed limit, left the lane and suffered a frontal impact. These collisions will be in the target populations for multiple measures, but they can only be prevented once by either one of these systems. This is addressed in the model by removing casualties prevented by one measure from the subsequent target population of the other measures. The impact of highly effective existing safety measures, which have been mandatory for a few years, but are still dispersing into the vehicle fleet is also modelled to reduce the remaining target populations for the proposed measures.

The cost of a policy option is calculated by multiplying per-vehicle cost estimates (input data) for each measure with the number of new vehicles of each vehicle category across EU-27 and UK that are equipped with the measure in the given year of the analysis according to the output of the fleet calculation model. In the economic calculation module, the monetary values of costs and benefits are subjected to inflation and discounting to determine their present value. The present values of benefits and costs exceeding the baseline, calculated for individual years and summed over the study period, are compared in order to arrive at cost-effectiveness estimates.

Benefits considered:

• monetary values of casualties prevented by safety measures

Costs considered:

• cost to vehicle manufacturers of fitment of safety measures to new vehicles